Over the last two decades, there has been a rising incidence of renal tumors, particularly, small renal masses (<4 cm) resulting in a downward size and stage migration. This has brought about a paradigm shift in the management of newly diagnosed renal masses, such that nephron-sparing surgery, minimally invasive techniques, and active surveillance are frequently considered preferable to the historical gold standard of open radical nephrectomy. Population-based cohort studies indicate, however, that the widespread adoption of these techniques has been relatively slow and incomplete leading to significant disparities in the delivery of care throughout the country. Further investigation is required to determine the barriers to diffusion of new techniques and technology as well as to ensure equal access to quality care in the United States.
Introduction and epidemiology
Renal cell carcinoma (RCC) accounts for approximately 3.5% of all malignancies and is the third most common cancer of the urinary tract. In 2010 there were an estimated 58,240 incident cases and 8210 cancer-related deaths. RCC ranks seventh among the leading causes of cancer in men and ninth among the leading causes of cancer among women in the United States. These figures also show an increasing incidence of RCC over the past few decades. Hollingsworth and colleagues estimated that the age-adjusted incidence increased from 7.1 to 10.8 cases per 100,000 of US population between 1983 and 2002.
Both this increasing incidence as well as a concomitant downward migration in clinical stage and primary tumor size at presentation are at least partly attributable to the increasing use of cross-sectional abdominal imaging in the diagnosis of renal masses. It has been estimated that at least 48% to 66% of RCC diagnoses occur as a result of cross-sectional imaging in an otherwise asymptomatic patient. Furthermore, the number of renal masses, both benign and malignant, discovered only at autopsy is declining, possibly because of increased detection before death.
This increasing incidence of RCC and the parallel increase in the national nephrectomy rate over the last 2 decades are emblematic of the changing clinical presentation and behavior of these tumors. Tumors are now heterogeneous in nature; 20% are entirely benign, with an additional 20% to 25% representing a potentially aggressive malignancy at the time of diagnosis. The changing landscape in tumor diagnosis and tumor biology has also resulted in changes in the management of these renal masses.
Overview of treatment options
Open Radical Nephrectomy
Robson is generally credited with establishing open radical nephrectomy (ORN) as the gold standard intervention for management of organ-confined and locally advanced renal cortical tumors. Key components of this technique included removal of the entire kidney with all surrounding perinephric tissue, resection of the ipsilateral adrenal gland, and regional lymph node dissection. Although this operation remained the standard of care for renal masses for more than 40 years, the increasing incidence of smaller and lower-stage tumors in the modern day has led to an evolution in the surgical management of this disease; namely, an increased acceptance of nephron-sparing as well as minimally invasive approaches. However, ORN remains indicated when nephron-sparing partial nephrectomy (PN) cannot be curative, such as instances of tumor thrombus, local invasion of surrounding organs, or significant lymphadenopathy.
Laparoscopic Radical Nephrectomy
Minimally invasive radical nephrectomy (RN) was first described by Clayman and colleagues in the early 1990s. Although its increased technical demands compared with ORN initially limited its acceptance, improved convalescence with demonstrably similar cancer control outcomes have led to its acceptance as an alternative standard of care in patients who require RN for RCC. Specifically, laparoscopic RN (LRN) has been linked to improved perioperative outcomes, including decreased blood loss, less pain, shorter length of stay, improved cosmesis, and faster return to work and normal activities. Although LRN is considered the preferred approach only in patients with tumors that are not amenable to PN, the adoption of laparoscopy to RN has nevertheless been slow compared with other laparoscopic treatments.
PN
Nephron-sparing approaches, particularly PN, have become increasingly popular over the last decade. Historically, open PN has been the primary approach for nephron-sparing surgery (NSS), the benefits of which derive from the preservation of renal parenchyma and renal function. Although originally reserved for patients with absolute indications such as instances of bilateral RCC, RCC in a solitary kidney, or RCC in the setting of preexisting kidney disease, it is now being routinely applied at tertiary-care centers for the management of localized renal tumors. This emphasis on tumor resection without compromising normal parenchyma is not without risk. PN, whether performed in open or laparoscopic fashion, is generally considered to be a more technically demanding operation than ORN or even LRN, with a resultant higher rate of complications such as hemorrhage, urinary fistula formation, ureteral obstruction, acute renal insufficiency, and infection. However, technical considerations aside, it has been shown that PN reduces the risk of chronic kidney disease (CKD) compared with RN and still achieves equivalent oncologic outcomes in tumors that measure less than 4 cm and even select tumors up to 7 cm in size. Similar to RN, laparoscopic and now robotic approaches have been applied to PN over time.
Ablative Approaches
The technical challenges associated with the use of nephron-sparing approaches (eg, its learning curve, necessary emphasis on limiting ischemia time, and a reportedly higher morbidity/complication rate) have led to the proposal of needle-based ablative technology as an alternative treatment of small renal masses. The efficacy of these ablative approaches is based on the placement of a needle or probe that, once placed into a target tumor, is able to induce a temperature-based lethality to all tissue within a fixed radius of ablation. This increasingly popular approach to the management of renal masses offers several advantages relative to surgery, including lower complication rates, shorter convalescence, absence of an ischemic insult, and the potential for outpatient management. However, these advantages aside, at present the oncologic efficacy of ablative techniques remains largely unproved. Moreover, it has been suggested that these techniques should be restricted to smaller renal masses (eg, <3 cm), because larger tumors require multiple probes and carry a higher risk of incomplete ablation. Another relative disadvantage to these techniques is the inability to acquire adequate tissue to provide complete pathologic staging of tumors or to confidently determine prognosis. Furthermore, an overall paucity of long-term oncologic data represents another notable drawback to this approach.
Active Surveillance
Although the perioperative morbidity associated with surgical intervention on renal masses has generally decreased as surgical techniques improve, some patients continue to be poor operative candidates or unwilling to accept the risks of surgical therapy. The mean age of patients undergoing RN and PN between 1988 and 2002 was 60.1 and 63.0 years, respectively. Thus, as patients age, competing health risks begin to compromise overall survival more significantly than many incidentally found renal lesions. A recent meta-analysis of 10 reports from the world literature evaluating untreated solid localized renal lesions reported a mean growth rate of 2.8 mm yearly and progression to metastatic disease in only 1% of cases at a mean follow-up of 38 months. However, because there are still no large-scale, prospective data regarding the risks associated with observing small renal lesions, pursuing active surveillance of a renal lesion continues to represent a calculated risk by the treating physician and the affected patient.
Overview of treatment options
Open Radical Nephrectomy
Robson is generally credited with establishing open radical nephrectomy (ORN) as the gold standard intervention for management of organ-confined and locally advanced renal cortical tumors. Key components of this technique included removal of the entire kidney with all surrounding perinephric tissue, resection of the ipsilateral adrenal gland, and regional lymph node dissection. Although this operation remained the standard of care for renal masses for more than 40 years, the increasing incidence of smaller and lower-stage tumors in the modern day has led to an evolution in the surgical management of this disease; namely, an increased acceptance of nephron-sparing as well as minimally invasive approaches. However, ORN remains indicated when nephron-sparing partial nephrectomy (PN) cannot be curative, such as instances of tumor thrombus, local invasion of surrounding organs, or significant lymphadenopathy.
Laparoscopic Radical Nephrectomy
Minimally invasive radical nephrectomy (RN) was first described by Clayman and colleagues in the early 1990s. Although its increased technical demands compared with ORN initially limited its acceptance, improved convalescence with demonstrably similar cancer control outcomes have led to its acceptance as an alternative standard of care in patients who require RN for RCC. Specifically, laparoscopic RN (LRN) has been linked to improved perioperative outcomes, including decreased blood loss, less pain, shorter length of stay, improved cosmesis, and faster return to work and normal activities. Although LRN is considered the preferred approach only in patients with tumors that are not amenable to PN, the adoption of laparoscopy to RN has nevertheless been slow compared with other laparoscopic treatments.
PN
Nephron-sparing approaches, particularly PN, have become increasingly popular over the last decade. Historically, open PN has been the primary approach for nephron-sparing surgery (NSS), the benefits of which derive from the preservation of renal parenchyma and renal function. Although originally reserved for patients with absolute indications such as instances of bilateral RCC, RCC in a solitary kidney, or RCC in the setting of preexisting kidney disease, it is now being routinely applied at tertiary-care centers for the management of localized renal tumors. This emphasis on tumor resection without compromising normal parenchyma is not without risk. PN, whether performed in open or laparoscopic fashion, is generally considered to be a more technically demanding operation than ORN or even LRN, with a resultant higher rate of complications such as hemorrhage, urinary fistula formation, ureteral obstruction, acute renal insufficiency, and infection. However, technical considerations aside, it has been shown that PN reduces the risk of chronic kidney disease (CKD) compared with RN and still achieves equivalent oncologic outcomes in tumors that measure less than 4 cm and even select tumors up to 7 cm in size. Similar to RN, laparoscopic and now robotic approaches have been applied to PN over time.
Ablative Approaches
The technical challenges associated with the use of nephron-sparing approaches (eg, its learning curve, necessary emphasis on limiting ischemia time, and a reportedly higher morbidity/complication rate) have led to the proposal of needle-based ablative technology as an alternative treatment of small renal masses. The efficacy of these ablative approaches is based on the placement of a needle or probe that, once placed into a target tumor, is able to induce a temperature-based lethality to all tissue within a fixed radius of ablation. This increasingly popular approach to the management of renal masses offers several advantages relative to surgery, including lower complication rates, shorter convalescence, absence of an ischemic insult, and the potential for outpatient management. However, these advantages aside, at present the oncologic efficacy of ablative techniques remains largely unproved. Moreover, it has been suggested that these techniques should be restricted to smaller renal masses (eg, <3 cm), because larger tumors require multiple probes and carry a higher risk of incomplete ablation. Another relative disadvantage to these techniques is the inability to acquire adequate tissue to provide complete pathologic staging of tumors or to confidently determine prognosis. Furthermore, an overall paucity of long-term oncologic data represents another notable drawback to this approach.
Active Surveillance
Although the perioperative morbidity associated with surgical intervention on renal masses has generally decreased as surgical techniques improve, some patients continue to be poor operative candidates or unwilling to accept the risks of surgical therapy. The mean age of patients undergoing RN and PN between 1988 and 2002 was 60.1 and 63.0 years, respectively. Thus, as patients age, competing health risks begin to compromise overall survival more significantly than many incidentally found renal lesions. A recent meta-analysis of 10 reports from the world literature evaluating untreated solid localized renal lesions reported a mean growth rate of 2.8 mm yearly and progression to metastatic disease in only 1% of cases at a mean follow-up of 38 months. However, because there are still no large-scale, prospective data regarding the risks associated with observing small renal lesions, pursuing active surveillance of a renal lesion continues to represent a calculated risk by the treating physician and the affected patient.
Trends in the adoption of LRN versus ORN
Although PN is now considered to be the reference standard for the management of small renal masses, RN remains indicated in instances in which PN is technically unfeasible. As outlined earlier, LRN has numerous demonstrable short-term benefits over ORN in perioperative outcomes such as decreased blood loss, shorter length of stay, less postoperative analgesia requirement, and faster return to work and normal activities. Consideration of these advantages coupled with excellent long-term oncologic outcomes has established LRN as a clearly superior alternative to ORN for tumors that are not amenable to PN. However, the adoption of this minimally invasive technique has been slow and incomplete since its initial introduction. Numerous population-based cohort studies have been done to assess any potential trends associated with the adoption of this technique throughout the United States.
The proportion of patients undergoing LRN has been generally increasing. Based on data abstracted from the Healthcare Cost and Use Project Nationwide Inpatient Sample (NIS) from 1991 to 2003, Miller and colleagues found year of treatment to be the most robust determinant of laparoscopic use. Specifically, it was reported that patients treated between 2000 and 2003 were 11 times more likely to have undergone laparoscopic surgery than those treated from 1991 to 1993. Using a more contemporary series based on data abstracted from the Surveillance Epidemiology and End Results (SEER) program Medicare database between 1995 and 2005, Filson and colleagues reported that this proportion increased from 1.4% in 1995 to 44.9% in 2005. Furthermore, analysis of the data with emphasis on trends in adoption by surgeons of LRN over time showed that the proportion of surgeons who performed at least 1 LRN in a given year increased from 1.7% in 1995 to 7.6% in 2000. After 2000, the rate of adoption accelerated considerably, reaching a peak of 42.6% in 2005. Despite these promising temporal trends, the adoption of laparoscopy for RCC has occurred at a slower rate than observed for other laparoscopic procedures such as cholecystectomy and fundoplication, both of which had surpassed open surgery (>50% of cases) within 5 years of their introduction.
Factors Influencing the Adoption of RN
Tumor characteristics
These population-based cohort studies have also identified trends in the use of laparoscopy based on differences in tumor characteristics. For example, receipt of LRN has been shown to be twice as likely for tumors less than 4 cm in size than for those greater than 7 cm (24% vs 12%). This finding is particularly puzzling considering that the results of a survey-based study suggested that 57% of urologists would offer laparoscopic surgery to a hypothetical patient presenting with a 6-cm organ-confined renal mass. Disparities in the use of laparoscopy have also been noted from tumor histology; however, these findings are of unclear significance because histology is frequently unknown at the time of surgical intervention.
Patient demographics
Several disparities in the use of laparoscopy have also been noted based on differences in patient characteristics. In their analysis of SEER data abstracted from 1995 to 2005, Filson and colleagues noted that whites were statistically significantly more likely to receive LRN than Hispanics (20% vs 12%). Furthermore, the investigators noted that those of high socioeconomic status were more likely to receive LRN than those of low socioeconomic status. In a similar vein, analysis of NIS data showed that those with private/health maintenance organization (HMO) insurance were more likely to undergo laparoscopic intervention compared with those with Medicare. In addition, those undergoing elective nephrectomy were more likely to receive laparoscopy than those undergoing urgent/emergent intervention.
Hospital-related and surgeon-related factors
The application of laparoscopy seems to differ in a variety of hospital-based factors as well. More specifically, a greater propensity toward laparoscopy occurs in urban compared with rural hospitals as well as in teaching compared with nonteaching hospitals. In addition, laparoscopy seems to be more commonly used in hospitals with a not-for-profit financial status compared with those that are for-profit. However, perhaps most telling of all is the association between the nephrectomy volume of a hospital and the frequency of laparoscopic nephrectomy. Miller and colleagues reported that the greatest proportion of laparoscopic use was observed in patients treated at teaching hospitals with an overall high annual nephrectomy volume and in patients treated between 2000 and 2003. Consequently, the investigators postulated that the acceleration in the adoption of laparoscopy occurring after the year 2000 was the primary result of the expanded use of oncologic renal laparoscopy in a select group of medical centers (ie, high-volume, urban, teaching hospitals) and did not therefore indicate widespread diffusion of laparoscopic management of renal tumors throughout the United States.
A host of surgeon-related factors seem to play a role in determining whether or not laparoscopy is used for renal masses. In 2008, using SEER data abstracted from 1997 to 2002, Miller and colleagues concluded that the percentage of variance among the use of laparoscopy attributable to unmeasured surgeon factors was substantially greater than that attributable to tumor size or patient demographics. Attempts to characterize these surgeon factors have elucidated that LRN is more likely among urologists who work in larger organizations (medical schools or HMOs), those who practice in urban environments, and those with a major academic affiliation.
Although the underuse of laparoscopy for management of renal tumors has been a matter of great concern over the last decade, the barriers to its widespread use remain unknown. The slow rate of adoption over the last 20 years is particularly perplexing when it is considered that within 3 years of the introduction of laparoscopic cholecystectomy, it was being used in more than 50% of cases nationwide and in up to 70% of cases by 4 years. Several potential reasons for this conspicuously slow rate of dissemination have been suggested, such as differences in market forces, motivations of physicians to provide innovative therapies, patient preferences, the steepness of the learning curve, or the competing desire to offer NSS; however, more research on this matter is required to draw concrete conclusions.
Trends in the adoption of PN
In 2009, the American Urological Association issued guidelines from panel consensus establishing surgical excision by PN as a reference standard for the management of clinical T1 RCC. These guidelines were based on several reports heralding equivalent long-term cancer-specific survival outcomes for PN and RN among clinical stage T1a and T1b renal tumors. The primary benefit of PN over RN is rooted in the preservation of normal renal parenchyma and thus renal function. RCC has been estimated to be responsible for 0.6% of cases of end-stage renal disease in the United States. Furthermore, within the last decade, a higher incidence of CKD in patients treated with RN as opposed to PN has been reported. It also seems likely, for these same reasons, that PN may also reduce the risk of adverse cardiovascular events and premature death compared with RN.
Despite the benefits of PN and the evidently equivalent oncologic outcomes, it has been suggested that PN remains underused in the treatment of small renal masses in the United States. Although some tertiary medical centers have reported PN rates approaching 90% for T1a renal tumors, population-based studies suggest a lower estimated overall rate of 20% to 40% of all nephrectomies.
There is a strong case for a persistent underuse of PN. Evidence of an underuse of PN nationwide can be clearly seen in Fig. 1 , which depicts both the national PN and RN rates for renal masses less than 4 cm in size abstracted from SEER data as well as the PN and RN rates at our own tertiary-care institution. The reasons for this apparent underuse have been a matter of great concern, and thus several population-based cohort studies have been conducted in an effort to identify which factors are associated with the use of PN versus RN in the United States.
Factors Influencing the Adoption of PN
The most robust factor associated with the rate of PN has been the passage of time, because multiple investigators have reported increasing annual rates of PN over the last 2 decades. For example, from SEER data abstracted from between 1988 and 2001, Miller and colleagues reported that the use of PN progressively increased for all tumors less than 7 cm in size. Specifically, a patient diagnosed in 2001 was nearly 5 times more likely to undergo PN than a patient diagnosed in 1988. More contemporary series have confirmed that this gradual increase in PN use for RCC has continued to the present day. Dulabon and colleagues, using more recent SEER data, reported that the PN/RN ratio increased in statistically significant fashion between 1996 and 2006. Using NIS data from 2003 to 2008, Kim and colleagues described a 90% increase in the annualized rate of PN per 100,000 individuals. However, despite these gradual increases, the investigators found that the overall rate of PN throughout the United States remained remarkably low. Even in 2008, PNs represented only 25.1% of all nephrectomy cases in the United States. Furthermore, these small increases in PN use do not seem to be reflected uniformly across different patient populations, surgeon populations, and hospitals.
Tumor size
A disparity in the PN rate between tumors of varying size has been described in the literature. In general, from SEER data from 1999 to 2006, it has been reported that for each 1-cm increase in tumor size, there was an associated 47% lower odds of undergoing PN. Similarly, the adoption of PN has therefore occurred most swiftly among patients with the smallest of tumors. In 1988 to 1989, 14% of tumors less than 2 cm underwent PN versus RN. This proportion had increased to 42% by 2000 to 2001. More recent data even suggest that between 2002 and 2004, the rate of PN exceeded that of RN in renal masses less than 2 cm.
By contrast, a slower rate of adoption has occurred for larger tumors. Among patients with tumors less than 4 cm in greatest dimension, only 5% underwent PN between 1988 and 1989; this had increased to only 20% by 2001 to 2002. Furthermore, over the same period, these T1a tumors were 3.8 times more likely to be treated with PN than T1b tumors. The PN rate finally exceeded 50% in 2004 in these T1a tumors.
Although the increasing rates of PN for very small renal tumors are promising, they still represent a gross underuse of the procedure, because PN is generally believed to offer equivalent oncologic outcomes in all tumors that measure less than 4 cm and even in select tumors up to 7 cm in size. When T1b tumors are considered, both the PN rate and the rate of adoption over time are even lower. Using SEER data, Baillargeon-Gagne and colleagues showed that the PN rate for T1b tumors increased from 2.0% in 1989 to 10.0% in 2004. However, the proportion of overall patients with RCC undergoing PN between 2000 and 2002 was only 12.3%.
Nephrometry score
Although tumor size has certainly been reported to affect the likelihood of receiving PN, it is not the only tumor characteristic that has preoperative value in the assessment of renal masses. A nephrometry scoring system can be used to grade the complexity of a tumor by its size, exophytic versus endophytic nature, and anatomic position. Although it has been reported that a low complexity nephrometry score increases the likelihood of PN in some single-institution series, this finding has never been assessed for validation in a large population-based cohort study. The impact and usefulness of the preoperative nephrometry score in guiding the surgical management of renal tumors remains an interesting question, which has yet to be definitively answered.
Age
There have been multiple reports of disparities among PN rates based on patient age. For example, NIS data abstracted from 1988 to 2002 suggested that patients older than 72 years were statistically significantly less likely to undergo PN compared with those 72 years or younger. Even when considering only NIS data from 1998 to 2002, Porter and Lin found that the odds of undergoing PN, compared with RN, decreased with each advancing age group from age less than 40 years, to age 40 to 59 years, to age 60 to 79 years, and those 80 years and older. More contemporary NIS data abstracted from 2003 to 2008 confirmed that patients aged 70 years or older were, in multivariate analysis, still approximately half as likely (odds ratio [OR] 0.51, P <.001) to undergo PN compared with their younger counterparts. Analysis of SEER data from between 1998 and 2001 also indicated that patients treated with PN were significantly younger than those treated with RN (mean age 60.3 vs 62.5, P <.01). This disparity was confirmed in more contemporary SEER data indicating that even between 1999 and 2006, those older than 70 years were significantly less likely to undergo PN compared with their younger counterparts. A significantly higher rate of PN among younger patients compared with older counterparts has been reported in European populations as well.
This age-based bias toward RN has been postulated by some to be the result of physician preference because it is thought to have fewer perioperative complications than PN. The disparity may be further perpetuated by the belief that the potential benefits of PN do not necessarily extend to the elderly population. However, the validity of this logic has been called into question by data suggesting that both RN and a sudden decrease in glomerular filtration rate (GFR) are independent predictors of premature death in elderly patients. Furthermore, PN reduces the risk of overtreating benign and indolent renal tumors in the elderly population who have lower GFR rates at baseline. However, theories that attempt to explain the bias against elderly patients in the use of PN are speculative, because no firm evidence to explain the disparity exists.
Gender
Differences in PN use between patients of opposite genders has become a matter of increasing concern. Gender disparities have been widely observed in other surgical procedures such as coronary artery bypass grafting. Early data regarding PN abstracted from NIS data from 1988 to 2002 showed that only 6.7% of women underwent PN versus 8.0% of men ( P <.0001). More contemporary data abstracted from the SEER database between 1999 and 2006 found that men were still 22% more likely to undergo PN compared with women. This disparity persisted even in a separate logistical model that included age, indicating that the bias was not limited to a specific age category. Even when controlling for various other risk factors such as tumor size, year of surgery, age, marital status, and place of SEER registry, gender has been shown to be a statistically significant risk factor predicting use of RN over PN. This finding has been reported in European populations as well. This observation is particularly concerning because women are more likely to be overtreated with RN given the greater likelihood of their being diagnosed with a benign tumor compared with men.
There may be many contributing reasons as to why this gender disparity exists both in the United States and internationally. One proposed theory attributes the disparity to physician bias, because it has been postulated that physicians may underestimate the risk of CKD in women based on their lower baseline serum creatinine levels. This error may be further compounded by the belief that women generally have fewer comorbid conditions and thus may accrue less overall benefit from the selection of PN, which is often considered to be a riskier and more technically demanding procedure. Alternatively, patient preference to undergo a more conservative procedure could be a second reasonable explanation. It has been similarly postulated that women may prefer a more definitive procedure to minimize the risk of recurrence. Finally, it is also conceivable that women may more frequently elect to undergo active surveillance on the basis that they are 2 to 4 times more likely to have benign or complex cystic renal tumors compared with men. However, although any or all of these factors may apply, the true causes of this gender bias in the usage of PN have not been adequately explained.
Patient comorbidities
The increased presence of comorbidities has been shown to reduce the likelihood of undergoing PN. Analysis of early NIS data showed that patients with a Charlson score of greater than 3 were found to be 60% less likely to undergo PN than those with scores of 0 to 2 between 1988 and 2001. In a more contemporary series encompassing NIS data from 2003 to 2008, those with an Elixhauser index of 2 to 3 or greater than 3 were found to be 83% and 67%, respectively, less likely to undergo PN compared with those with a score of 0 to 1. This trend has been reported in the European population as well; Fedeli and colleagues reported that patients with a Charlson comorbidity index 1 or greater were significantly less likely to undergo PN compared with counterparts with Charlson index 0 on both single and multivariate analysis.
Although at face value, the selection of RN in sicker patients in an attempt to avoid a higher rate of perioperative morbidity and complications may seem reasonable, it could be conversely argued that this population of patients with a greater number of comorbidities has the most to gain from a nephron-sparing approach with respect to their long-term renal, cardiovascular, and survival outcomes. Furthermore, even if PN could not be pursued secondary to a patient’s extensive comorbidities, it stands to reason that active surveillance rather than RN may offer better long-term outcomes. The ideal rate of PN in populations with extensive comorbidities remains unknown.
Other patient demographic factors
Race has been shown to be an independent predictor of PN usage as well in some population-based cohort studies. NIS data abstracted from 1988 to 2001 showed that blacks and Hispanics were more likely to undergo PN than the reference race of whites. Using more recent NIS data, Kim and colleagues recently reported that blacks still had statistically significant higher odds of undergoing PN compared with whites (OR 1.11, P = .02). However, this finding may represent the influence of an alternate confounding risk factor because there have been reports of no significant disparity between race on some multivariate analyses of contemporary SEER data.
There have been numerous other disparities in the usage of PN identified by various investigators from various patient demographic factors. Different studies have suggested that those with private insurance, who are married and undergoing elective (as opposed to emergent) resection are more likely to undergo PN for renal lesions. However, long-term trends investigating the application of PN to these patient populations have not been nearly as thoroughly examined as those regarding age, race, gender, and the presence of comorbidities.
Hospital and surgeon characteristics
The use of PN may vary by some hospital-level factors as well. It has been reported that patients treated at teaching hospitals may be more likely to undergo PN compared with those treated at nonteaching hospitals. Using NIS data from between 1988 and 2002, Hollenbeck and colleagues reported that the PN rate at teaching hospitals was 10.5% versus only 5.2% at nonteaching hospitals ( P <.0001). When restricting the analysis only to NIS data from 1998 to 2002, Porter and colleagues found that those treated in teaching hospitals were still nearly twice as likely to undergo PN compared with the referent group treated at nonteaching hospitals (OR 1.95, P <.001). This trend has persisted even in the most contemporary of series; Kim and colleagues, using NIS data from between 2003 and 2008, reported that patients treated at teaching hospitals were still 1.3 times more likely to undergo PN compared with those treated at nonteaching hospitals (OR 1.31, P <.001).
A similar increased likelihood of undergoing PN has been witnessed in urban settings. Analysis of NIS data from 1998 to 2002 led to the conclusion that those treated in urban settings had a marginally higher likelihood of undergoing PN than their rural counterparts. Analysis of the more recent NIS data from 2003 to 2008 revealed that this disparity has not improved, because those treated in urban hospitals were still more likely to undergo PN (OR 1.13, P = .05). It was also noted that patients treated at hospitals located in the northeast were significantly more likely to undergo PN compared with those treated in the midwest (OR 0.76), south (OR 0.76), or west (OR 0.75) United States. Kim and colleagues also reported that patients treated in hospitals located in ZIP (zone improvement plan) codes with median household annual income exceeding $63,000 were significantly more likely to undergo PN compared with their counterparts treated in ZIP codes with median annual income less than $39,000. The question of which of the hospital region-oriented characteristics has the strongest effect on likelihood of PN remains unknown.
Hospital nephrectomy volume has also been shown to be an independent predictor of the frequency of PN utilization by some population-based cohort studies. From NIS data from 1988 to 2002, Hollenbeck and colleagues reported that the patients treated at hospitals with annual nephrectomy volume greater than or equal to 28 were 2.5 times more likely to undergo PN compared with patients treated at very-low-volume hospitals (annual volume 1–5). A similarly significant trend showing increasing use of PN with increasing annual nephrectomy volume was also seen in hospitals with volume 17 to 27 (OR 1.7), 11 to 16 (OR 1.2), and 6 to 10 (OR 1.1) compared with a referent very-low-volume group. This trend toward an increased likelihood of PN at higher-volume nephrectomy centers was confirmed in studies based on NIS data from 1998 to 2002 and from 2003 to 2008. A similar disparity in PN rate between hospitals by nephrectomy volume has been observed in European populations as well. Although the observation that PN is more likely at high-nephrectomy-volume hospitals is unmistakable, it is not known whether this is the result of a high rate of referrals of PN patients to high-volume centers or the inappropriate use of RN at low-volume centers. More research on this topic is required to answer this question.
Differences in surgeon characteristics are likely to play a role in the determination of whether PN is used in the treatment of a renal mass. Miller and colleagues reported that proportion of variance in use of PN due to surgeon-level determinants was greater than for any other factor except for tumor size. One example of a surgeon-related characteristic that may affect the rate of PN utilization is annual surgeon nephrectomy volume. When Porter and Lin analyzed NIS data from 1998 to 2002 by stratifying patients into quartiles based on the operating surgeon’s nephrectomy volume, they found a statistically significant increase in PN usage with each progressive increase in quartile. Similar to the discussion regarding the data surrounding variations in PN usage between hospitals with varying nephrectomy volumes, it is unknown whether this trend represents a high rate of referrals of PN candidates to higher-volume surgeons or the inappropriate usage of RN by low-volume nephrectomists.
International trends
Similar trends have been observed internationally as well. For example, from data extracted from England’s Hospital Episode Statistics database, Nuttall and colleagues found that PN was performed in less than 5% of surgeries for renal malignancies in 2000 to 2001. The European rate of adoption in the 10 years since then has been similarly sluggish. Using a regional archive of hospital discharge records from the Veneto region of northeastern Italy, Fedeli and colleagues reported that the usage of PN increased over the course of their study from being used in 22% of all oncologic kidney surgeries in 1999 to 31% in 2007. However, as has been described in the US literature, European tertiary-care centers have been quicker to use PN. Zini and colleagues, after analyzing data regarding all T1-T2N0M0 tumors from 6 European tertiary-care centers, reported that the overall PN rate increased from 11.2% between 1987 and 1991 to 37.4% from 2000 to 2003. Between 2004 and 2007, the PN rate surpassed that of RN in these tertiary-care centers, reaching 50.1%. When stratified into groups defined by tumor size less than 2 cm, tumor size between 2.1 and 4 cm, and tumor size between 4.1 and 7 cm, the investigators reported PN rates between 2004 and 2007 of 86.3%, 69.3%, and 35.3%, respectively. Although there have been single-institution reports of US tertiary-care centers with PN rates of up to 90% for small T1a tumors and 60% for T1b tumors, large population-based cohort studies have consistently indicated a lower and more slowly increasing PN rate nationwide.
The effect of laparoscopy on the adoption of PN
It has been suggested that the widespread acceptance of laparoscopy has contributed to the underuse of PN for small renal masses. This conjecture is based on the premise that technical rigors and perioperative risk associated with performing laparoscopic PN (LPN) has left many urologists with the choice of choosing between a minimally invasive or a nephron-sparing surgical approach to renal masses (ie, LRN vs OPN). Although this question has been investigated by some population-based cohort studies, the results have been conflicting. Using the population-based Ontario cancer registry, Abouassaly and colleagues found that the odds of PN increased by 18% per year until January 2003 and subsequently decreased by 12% per year. They consequently concluded that the introduction of LRN coincided with decreased use and adoption of PN. By contrast, Perotti and colleagues, after retrospectively analyzing their database of patients with T1 renal masses, concluded that laparoscopy did not seem to result in an underuse of PN.
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