Leiomyoma of the colorectum is a rare benign tumor arising from the muscularis layer of the colorectal wall of adults, predominantly males with a median age of 60 years. It presents as a well-delineated, white, and firm polypoid nodule. A conservative excision is therapeutic.

Lipoma of the large bowel is a rare, benign, often single, and submucosal adipose-tissue tumor. Occasionally, lipomas may present as multiple yellowish polyps. Lipoma is seen in adults and affects both genders. Large lipomas can cause constipation, abdominal pain, rectal bleeding, and intussusception.

Schwannoma is a rare, benign colorectal tumor of adults and affects both genders equally. The tumor is usually a well-circumscribed submucosal mass.

Ectopic pancreatic tissue is a relatively frequent congenital anomaly. It is most common in the upper gastrointestinal tract, including the stomach, duodenum, and jejunum, and less common in the lower GI tract, particularly the colon.

Gross examination reveals a well-circumscribed, lobulated, yellow tan, firm nodule. Central umbilication is seen in cases located in the submucosa. Histologic examination shows normal pancreatic acini and ducts. Islet cells are seen in less than half of the cases. Ectopic pancreas is immunoreactive for amylase, lipase, and trypsinogen. No genetic abnormality is detected. Cytology smears show clusters of benign pancreatic acini and ductal epithelium (Fig. 6.7).

Gastric heterotopia is a rare condition that may occur in the anus and rectum. It is slightly more common in males than in females, with a mean age of 21 years. Patients complain of rectal pain, bleeding, or irritable bowel syndrome. In asymptomatic patients gastric heterotopia can be identified incidentally on cancer screening. The lesion may appear as a polyp, diverticulum, or ulcer on colonoscopy. A fundic type gastric mucosa is the most common histologic finding. Cytology smears show benign columnar, parietal, and oxyntic cells.

Colorectal carcinoma is the most common carcinoma of the gastrointestinal tract. It is the third most common cancer in the United States, affecting males and females equally at a mean age of 60 years. It is the second leading cancer-related cause of death. The pathogenesis of colorectal carcinoma is related to personal, familial, and environmental risk factors. Individuals with a history of inflammatory bowel disease (ulcerative colitis, Crohn’s disease), adenomas (tubular, villous, or tubulovillous), sessile serrated polyps, prior colorectal cancer, and/or those who have a first-degree relative with invasive colorectal cancer are at high risk of developing colorectal cancer. Inherited syndromes, such as Lynch syndrome (also known as hereditary nonpolyposis colorectal cancer), polyposis syndromes including classical familial adenomatous polyposis, attenuated familial adenomatous polyposis, MUTYH-associated polyposis (MAP), juvenile polyposis syndrome, Peutz-Jeghers syndrome, serrated polyposis syndrome, Cowden syndrome, and Li-Fraumeni syndrome also are associated with a high risk of colorectal cancer. Diets high in red meat or processed meat and low in fiber, as well as smoking, alcohol consumption, a high body mass index, and a low level of physical activity are considered personal lifestyle risk factors. Colorectal cancer screening, recommended at age of 50 for men and women with average risk, has decreased the mortality rate due to colorectal cancer because of early detection of precancerous lesions. Colorectal cancer most commonly occurs in the cecum, ascending colon, sigmoid colon, and rarely in the anal canal (where it must be distinguished from extension from a rectal primary). The tumor is either exophytic or infiltrating.

Primary colonic squamous carcinoma is exceedingly rare. Risk factors include mechanical trauma, local radiotherapy, and chronic schistosomiasis. In the absence of risk factors or a history of a distant squamous primary, colonic squamous carcinoma is a diagnosis of exclusion. Squamous cell carcinoma of the anus (15 % of anal cancers) and the anal canal (80 % of anal cancers) is seen in adults and mainly affects females in the sixth and seventh decades of life. In the last 20 years, there has been a shift in the age of diagnosis, with a higher incidence in younger individuals, more commonly in those with immunosuppression, particularly HIV. Rectal bleeding, a nodular or ulcerated mass, and pain are common clinical findings. The tumor can invade deeply in perirectal soft tissue, both proximally and distally. The treatment of choice includes combined neoadjuvant chemoradiation therapy, which achieves a remarkably good response, followed by radical surgery (abdominoperineal resection) only for persistent or locally recurrent tumors.