and Cam5.2), sarcoma (desmin, smooth muscle actin, CD34, and KIT), melanoma (S100, Melan-A, HMB-45, SOX 10, MiTF, and tyrosinase), and lymphoma (CD3, CD20, and CD45). Other stains for rare entities include germ cell tumor markers (PLAP, Oct4, α-fetoprotein [AFP], SALL4, and human chorionic gonadotropin [hCG]), plasmacytoma (CD138 and MUM1), and rhabdoid tumor or epithelioid sarcoma (INI1). Of note, it is often important to use multiple markers because poorly differentiated malignancies may have focal expression or lose expression of some lineage markers. Once the broad lineage of the tumor has
been determined, more specific immunostains can be performed for further tumor subclassification. Commonly used immunostain markers are listed in Table 31.2; however, none of immunostaining markers is perfect for a specific entity and there are many pitfalls when interpreting immunostaining results.
Table 31.1 Commonly used serum tumor markers
and albumin in situ hybridization); squamous cell or urothelial carcinoma (CK5/6, CK903, p40, GATA-3, and p63); neuroendocrine tumors including small cell carcinoma (synaptophysin and chromogranin); mesothelioma (calretinin, WT-1, and D2-40); acinar cell carcinoma (trypsin and Periodic acid-Schiff [PAS]). After a diagnosis of adenocarcinoma is established, a combination of CK7/CK20 can be used with other organ specific markers for lung, gastrointestinal, breast, prostate, or other origins. Different CK7/CK20 staining
patterns can provide useful clues for determining tumor origin and deciding second round of immunostain work up (Table 31.3). Of note, there are no organ specific markers for squamous cell carcinoma. In addition, adenocarcinoma arising in upper gastrointestinal tract or pancreatobiliary tract can have similar morphology and immunophenotype.
Table 31.2 Commonly used tumor origin markers and some pitfalls for primary and metastatic tumors of the liver
Table 31.3 General CK7 and CK20 staining patterns
carcinoma, neuroendocrine tumors, and acinar cell carcinomas (Figs. 31.1 and 31.2). Squamous differentiation is characterized by keratinization with squamous pearl formation, large cells with glassy eosinophilic cytoplasm, distinct cell borders, and intercellular bridge (Fig. 31.3). If a glandular component is identified in addition to squamous differentiation, a diagnosis of adenosquamous carcinoma is made.
Figure 31.4 Neuroendocrine tumor. Organoid growth pattern with “salt-and-pepper” chromatin pattern without conspicuous nucleoli typically seen in neuroendocrine tumor.
Figure 31.6 Pancreatic solid pseudopapillary tumor. Eosinophilic globules in metastatic pancreatic solid pseudopapillary tumor.
renal cell carcinomas, acinar cell carcinoma, adrenal cortical carcinomas, melanoma, and epithelioid angiomyolipomas. Hepatocellular carcinoma is usually excluded by a panel of multiple hepatocellular markers, such as HepPar-1, arginase, glypican-3, and albumin in situ hybridization. Polyclonal carcinoembryonic antigen (CEA) and CD10 are older markers of hepatic differentiation that depend on identifying a canalicular staining pattern but are not widely used anymore because newer stains have better performance characteristics. In our practice, we typically start with HepPar-1 and/or arginase if the morphological impression is a well to moderately differentiated hepatocellular carcinoma. Positive staining for one of them can usually confirm the diagnosis in morphologically consistent well or moderately differentiated hepatocellular carcinomas. If the immunostains are negative, then tests for other markers including glypican-3 and albumin in situ hybridization are used. Additional stains are used to exclude other tumors depending on the morphology and the clinical findings.
to the possibility of metastatic hepatoid carcinoma include tumors showing only focal areas of hepatic differentiation on H&E, histories of mass lesions in other organs such as the upper gastrointestinal tract, pancreas, or lung, and atypical immunophenotypes. Examples of immunophenotypes that are atypical for hepatocellular carcinoma include strong and diffuse TTF1 nuclear staining or strong and diffuse CDX2 staining. Of note, other nonhepatoid carcinomas may also be positive for hepatic markers (HepPar-1, glypican 3, arginase, or albumin in situ hybridization), but if they do not have hepatoid morphology, then they are not classified as hepatoid carcinomas.