Application of immunohistochemistry to liver and gastrointestinal neoplasms: liver, stomach, colon, and pancreas

Recommendations on maximising the clinical value of tissue in the management of patients with intrahepatic cholangiocarcinoma

Background & Aims

Patients with intrahepatic cholangiocarcinoma can now be managed with targeted therapies directed against specific molecular alterations. Consequently, tissue samples submitted to the pathology department must produce molecular information in addition to a diagnosis or, for resection specimens, staging information. The pathologist's role when evaluating these specimens has therefore changed to accommodate such personalised approaches.

Methods

We developed recommendations and guidance for pathologists by conducting a systematic review of existing guidance to generate candidate statements followed by an international Delphi process. Fifty-nine pathologists from 28 countries in six continents rated statements mapped to all elements of the specimen pathway from receipt in the pathology department to authorisation of the final written report. A separate survey of 'end-users' of the report including surgeons, oncologists, and gastroenterologists was undertaken to evaluate what information should be included in the written report to enable appropriate patient management.

Results

Forty-eight statements reached consensus for inclusion in the guidance including 10 statements about the content of the written report that also reached consensus by end-user participants. A reporting proforma to allow easy inclusion of the recommended data points was developed.

Conclusions

These guiding principles and recommendations provide a framework to allow pathologists reporting on patients with intrahepatic cholangiocarcinoma to maximise the informational yield of specimens required for personalised patient management.

Impact and Implications

Biopsy or resection lesional tissue from intrahepatic cholangiocarcinoma must yield information about the molecular abnormalities within the tumour that define suitability for personalised therapies in addition to a diagnosis and staging information. Here, we have developed international consensus guidance for pathologists that report such cases using a Delphi process that sought the views of both pathologists and 'end-users of pathology reports. The guide highlights the need to report cases in a way that preserves tissue for molecular testing and emphasises that reporting requires interpretation of histological characteristics within the broader clinical and radiological context. The guide will allow pathologists to report cases of intrahepatic cholangiocarcinoma in a uniform manner that maximises the value of the tissue received to facilitate optimal multidisciplinary patient management.

An Update on the Role of Immunohistochemistry in the Evaluation of Pancreatic/Liver/Gastrointestinal Luminal Tract Disorders

CONTEXT.—

Immunohistochemistry serves as an ancillary diagnostic tool for a wide variety of neoplastic and nonneoplastic disorders, including infections, workup of inflammatory conditions, and subtyping neoplasms of the pancreas/liver/gastrointestinal luminal tract. In addition, immunohistochemistry is also used to detect a variety of prognostic and predictive molecular biomarkers for carcinomas of the pancreas, liver, and gastrointestinal luminal tract.

OBJECTIVE.—

To highlight an update on the role of immunohistochemistry in the evaluation of pancreatic/liver/gastrointestinal luminal tract disorders.

DATA SOURCES.—

Literature review and authors' research data and personal practice experience were used.

CONCLUSIONS.—

Immunohistochemistry is a valuable tool, assisting in the diagnosis of problematic tumors and benign lesions of the pancreas, liver, and gastrointestinal luminal tract, and also in the prediction of prognosis and therapeutic response for carcinomas of the pancreas, liver, and gastrointestinal luminal tract.

Evaluation of Immune Infiltration Based on Image Plus Helps Predict the Prognosis of Stage III Gastric Cancer Patients with Significantly Different Outcomes in Northeastern China

Gastric cancer (GC) might have significantly different outcomes within the same AJCC/UICC-TNM stage. The purpose of this study is to help predict the different prognosis through the pattern of immune cell infiltration. We retrospectively analyzed 2605 patients who underwent radical gastrectomy in the Harbin Medical University Cancer Hospital between 2002 and 2013. For stage III with significantly different survival probability, we analyzed the relationship between immune cell surface antigen and survival in TCGA dataset. Furthermore, 200 cases in stage III GC with different survival outcomes were randomly selected for immunohistochemical verification. Image Plus software was used to evaluate the area of immune cell infiltration. We found that patients in stage III had significantly different outcomes. Bioinformatics analysis showed that there was a significant negative correlation between the expression of immune cell surface antigen and prognosis. In order to investigate whether immune infiltration can distinguish GC patients in stage III with differences in prognosis, we verified by immunohistochemistry that CD4+ T cells, CD20+ B cells, and CD177+ neutrophils infiltrated more in group B with better prognosis; CD8+ T cells, CD68+ macrophages, and CD117+ mast cells infiltrated more in group A with poor prognosis. CD117+ mast cells have the same trend of predicting significance for prognosis in the RNA and protein levels. In conclusion, patients with GC in northeastern China have significant prognostic differences only in stage III. CD117+ mast cells may be important evaluation factors in further studies of Immunoscore.

Different cellular properties and loss of nuclear signalling of porcine epidermal growth factor receptor with aging

Epidermal growth factor (EGF) has important physiological functions that are mediated by the epidermal growth factor receptor (EGFR); however, to date, the changes in cellular behaviours and signalling properties of EGF/EGFR with aging remain unclear in the pig tissue models. Hence, the present study used porcine hepatocytes as a model to explore this issue. The study revealed the following results: 1) EGF could activate the intra-cellular signalling pathways in a time- and dose-dependent manner both in the young- and aged-pig hepatocytes, EGF induced tyrosine phosphorylation of EGFR, signal transducers and activators of transcription 3 (STAT3), protein kinase B (AKT) and extra-cellular signal-regulated kinase 1/2 (ERK1/2). Nevertheless, the EGF's signalling ability in the aged-pig hepatocytes was significantly reduced compared with that of the young-pig hepatocytes; 2) although EGF/EGFR can still be internalised into cells in a time-dependent manner with aging, the endocytic pathway differs between the young- and aged-pig hepatocytes. Furthermore, the results of the present study indicated that caveolin may play a pivotal role in the endocytosis of EGF/EGFR in the aged-pig hepatocytes, which is different from that of EGF/EGFR's endocytosis in young-pig hepatocytes; 3) It is well-known that EGFR carried out its biological effects via two signalling pathways, cytoplasmic pathway (traditional) and nuclear pathway; however, we found that the nuclear localisation of EGFR was significantly reduced in the aged-pig hepatocytes, which indicated that EGFR may lose its nuclear pathway with aging. Collectively, the present study lays the foundation for further study regarding the biological functional changes occurring in EGF/EGFR with aging.

Macrophage spatial heterogeneity in gastric cancer defined by multiplex immunohistochemistry

Tumor-associated macrophages (TAMs), one of the most abundant immune components in gastric cancer (GC), are difficult to characterize due to their heterogeneity. Multiple approaches have been used to elucidate the issue, however, due to the tissue-destructive nature of most of these methods, the spatial distribution of TAMs in situ remains unclear. Here we probe the relationship between tumor context and TAM heterogeneity by multiplex immunohistochemistry of 56 human GC cases. Using distinct expression marker profiles on TAMs, we report seven predominant populations distributed between tumor and non-tumor tissue. TAM population-associated gene signatures reflect their heterogeneity and polarization in situ. Increased density of CD163+ (CD206-) TAMs with concurrent high CD68 expression is associated with upregulated immune-signaling and improved patient survival by univariate, but not multivariate analysis. CD68-only and CD206+ TAMs are correlated with high PDL1 expression.

Malignant potential of epithelioid angiomyolipomas of the liver: A case report and comprehensive review of the literature

Hepatic epithelioid angiomyolipoma (HEAML) is a rare mesenchymal tumor that has been reported to have malignant potential. We herein describe a rare case of atypical HEAML. A 43-year-old Caucasian male patient visited his general practitioner due to a productive cough persisting for >2 months. During evaluation with several imaging tests, a chest computed tomography (CT) incidentally revealed a well-demarcated lesion in the caudate lobe of the liver, sized 7 cm. An abdominal magnetic resonance imaging examination confirmed the findings of the CT. The possibility of hepatocellular carcinoma at that time could not be excluded. Due to inconclusive cross-sectional imaging, the patient underwent left hepatectomy with additional resection of segment I. The patient's postoperative course was uneventful. A diagnosis of 'atypical' HEAML was established in the present case. The majority of HEAMLs are considered to be benign, although there are several reported cases exhibiting malignant behavior, such as tumor growth, presence of atypical cells, recurrence after surgical resection, metastasis and invasive growth into the liver parenchyma and alongside the vessels. From 2000 onwards, 19 cases of malignant hepatic AML have been reported. Malignant transformation is considered to occur mostly in the epithelioid subtype. To that end, when epithelioid or atypical characteristics are identified on preoperative biopsy, resection is indicated due to the high probability of malignancy.

Intrahepatic Biliary Metastasis of Colonic Adenocarcinoma: A Case Report With Immunohistochemical Analysis

Although intrabiliary metastasis of carcinoma in the liver is unusual, intraductal and/or intraepithelial spread of cancer cells along intrahepatic bile ducts is now well recognized as hepatic metastasis. However, several clinical and laboratory findings, including images, lead us to differentially diagnose from primary intrahepatic cholangiocarcinoma. We report here on a case of colonic adenocarcinoma that metastasized to the liver with spread along with the intrahepatic bile duct of S5/6 area. The patient was a 51-year-old man and clinically diagnosed liver metastasis of sigmoid colon cancer (tub2, pMP, ly1, v0, n0), which was diagnosed and treated by sigmoidectomy 7 years ago. The right hepatic lobectomy was performed in March 2016 and histopathological examination revealed that moderately differentiated adenocarcinoma proliferated along the epithelium of intrahepatic bile ducts. Immunohistochemistry (IHC) showed that cancer cells in the intrahepatic bile ducts were positive for CK20, CDX2, CK17 and CK19, but negative for CK7, MUC-5AC, MUC-2 and CA19-9. The findings were almost the same as those of the sigmoid colon cancer removed in July 2009. We finally diagnosed the liver tumor as intrahepatic biliary metastasis of sigmoid colon cancer. Patients with liver metastasis of cancer are hard to be detected biliary invasion and spread on diagnostic image examination. Knowledge of distinctive morphological and IHC features can help to accurately diagnose this rare intrahepatic biliary metastasis of colonic cancer in routine pathological diagnostic procedures.

Application of immunohistochemistry in gastrointestinal and liver neoplasms: new markers and evolving practice

CONTEXT

Diagnosis of primary gastrointestinal and liver neoplasms is usually straightforward. Immunohistochemistry is most helpful to differentiate metastatic carcinomas with morphologic similarity and to resolve tumors of unknown origin. Recently, several new markers highly sensitive and specific for primary liver and gastrointestinal tumors have been discovered. Their potential diagnostic application has not been widely appreciated by general practicing pathologists. In addition, a new trend in immunohistochemistry application has started, focusing on assessing predictive markers (such as human epidermal growth factor receptor 2) and mutation-specific markers (v-raf murine sarcoma viral oncogene homolog B V600E) to directly guide clinical management. Practicing pathologists need to be aware of and prepared for this evolving trend.

OBJECTIVES

To summarize the usefulness of several recently discovered immunohistochemical markers in the study of gastrointestinal and liver tumors; to suggest the most current and effective immunohistochemical panels addressing common diagnostic challenges for these tumors; to share practical experience and useful tips for human epidermal growth factor receptor 2 testing in gastric and gastroesophageal junction adenocarcinoma and v-raf murine sarcoma viral oncogene homolog B V600E immunohistochemistry in colorectal carcinoma.

DATA SOURCES

Sources include literature review, and authors' research data and practice experience. The cases illustrated are selected from the pathology archives of the Geisinger Medical Center (Danville, Pennsylvania).

CONCLUSIONS

Application of immunohistochemistry in gastrointestinal and liver tumors continues to evolve. New tumor-specific markers constantly emerge and help pathologists to further improve diagnostic accuracy. Assessment of predictive and prognostic markers by immunohistochemistry in routine pathologic diagnosis is a new trend and will greatly facilitate the advancement of personalized cancer therapy.

Utility of immunohistochemistry in the pancreatobiliary tract

CONTEXT

Immunohistochemistry has become a useful ancillary study in the identification and classification of pancreatic neoplasms. The diagnostic accuracy has been significantly improved because of the continuous discoveries of tumor-associated biomarkers and the development of effective immunohistochemical panels.

OBJECTIVES

To identify and classify pancreatic neoplasms by immunohistochemistry.

DATA SOURCES

Literature review and authors' research data and personal practice experience were used.

CONCLUSIONS

To better guide therapeutic decisions and predict the prognostic outcome, it is crucial to make an accurate diagnosis of a pancreatic neoplasm. Application of appropriate immunohistochemical panels enables pathologists to differentiate pancreaticobiliary adenocarcinomas from reactive conditions and to identify rare types of pancreatic neoplasms. Knowing the utilities and pitfalls of each tumor-associated biomarker is essential to avoiding a potential diagnostic error because an absolutely cancer-specific biomarker does not exist. This article reviews frequently used tumor-associated biomarkers, provides lists of effective immunohistochemical panels, and recommends a diagnostic algorithm as a standard approach to pancreatic neoplasms.

Pituitary protein 7B2 plasma levels in patients with liver disease: Comparisons with other hormones and neuropeptides

7B2, a protein initially isolated from the porcine pituitary gland, has been identified in numerous animal and human tissues, with the highest concentrations in the pituitary and hypothalamus. The 7B2 molecule is highly evolutionarily conserved and is considered to be indispensable in the function and regulation of proprotein convertase 2 (PC2). In the present study, the plasma 7B2 immunoreactivity (7B2-IR) of 18 patients with liver disease was studied. Of these patients, seven (three male and four female), aged 37–67 [54.6±13.5 (SD)] years, suffered from liver cirrhosis of cryptogenic (n=2) or alcoholic (n=5) aetiology. The remaining 11 patients (four male and seven female), aged 22–76 [56.1±17.6 (SD)] years, suffered from miscellaneous liver abnormalities. The clinical diagnosis was confirmed in the majority of patients by the histological examination of a percutaneous liver biopsy or by appropriate radiological investigations. Plasma bilirubin, alkaline phosphatase, aspartate aminotransferase, albumin, prothrombin time, electrolytes, urea and creatinine were measured. The plasma 7B2-IR levels were estimated using a sensitive radioimmunoassay (RIA), and the elution position of 7B2-IR was verified by gel chromatography. The mean plasma 7B2-IR concentration in patients with liver disease was 99.44±15.9 pmol/l. In the patients with hepatocellular damage due to metastatic tumours [Ca bronchus, carcinoid (n=6)], the 7B2-IR concentrations were significantly higher [185±36.9 pmol/l, (P<0.05)] compared with the overall subjects with liver damage. The results of the present study demonstrate that 7B2-IR is increased in liver disease, with the highest levels detected in patients with tumourous liver conditions.

Distinct claudin expression profiles of hepatocellular carcinoma and metastatic colorectal and pancreatic carcinomas

Tight junction proteins, including claudins, are often dysregulated during carcinogenesis and tumor progression. Moreover, the claudin expression pattern usually varies between different tumor entities. We aimed to investigate claudin expression profiles of primary and metastatic liver malignancies. We analyzed claudin-1, -2, -3, -4, and -7 expression by quantitative immunohistochemistry and real-time RT-PCR, respectively. Twenty hepatocellular carcinomas (HCCs) and liver metastases of 20 colorectal adenocarcinomas (CRLMs) and 15 pancreatic adenocarcinomas (PLMs) were studied together with paired surrounding non-tumorous liver samples and 5 normal liver samples. Strong claudin-3 and -7 immunohistochemical positivities were detected in CRLM samples, each with significantly stronger staining when compared with HCC and PLM groups. Claudin-1 protein was found highly expressed in CRLM, in contrast to lower expression in PLM and HCC. CRLMs and PLMs also were strongly positive for claudin-4, while being virtually undetectable in HCC. Claudin-2 showed strong positivity in non-tumorous liver tissue, whereas significantly weaker positivity was observed in all tumors. Differences in mRNA expression were mostly similar to those found by immunohistochemistry. In conclusion, HCC and both CRLM and PLM display distinct claudin expression profiles, which might provide better understanding of the pathobiology of these lesions and might be used for differential diagnosis.

Immunohistochemistry of colorectal carcinoma: current practice and evolving applications

The relatively high incidence of adenocarcinoma of the colon and rectum (colorectal carcinoma) in the general population makes its pathologic diagnosis one of the more frequent exercises in anatomical pathology. Although typically mundane in the primary setting, the correct identification of metastatic colorectal carcinoma or exclusion of metastatic disease from carcinoma arising in other anatomical foci can be problematic. The advent of targeted therapies and refinement of more traditional cytotoxic chemotherapeutic regimens mandates not only a more confident appraisal of site of origin but also assessment of those tumor-specific features that may alter therapeutic decisions. Despite the exponential increase in our understanding of the molecular pathogenesis of colorectal carcinoma, immunohistochemistry remains the foundation for resolution of these problematic cases and the number of antibodies available to the practicing pathologist continues to expand at a steady rate. In some cases, immunohistochemistry may also provide valuable prognostic information, either independently or as a surrogate marker for a specific route of carcinogenesis such as microsatellite instability. This review will focus on the use of new and more established immunohistochemistry markers in the diagnosis of colorectal carcinoma, with an emphasis on aberrant staining patterns of the various colorectal carcinoma subtypes as well as the utility of these markers in specific differential diagnostic settings.

Reduced Popdc3 expression correlates with high risk and poor survival in patients with gastric cancer

AIM

To investigate the expression of Popeye domain containing 3 (Popdc3) and its correlation with clinicopathological features and prognosis of gastric cancer.

METHODS

The method of immunohistochemistry was used to investigate the expression of Popdc3 in 306 cases of human gastric cancer and 84 noncancerous gastric tissues. Simultaneously, the relationship between Popdc3 expression and the survival of the patients was retrospectively analyzed.

RESULTS

Popdc3 was detected in 72 (85.71%) of 84 human nontumor mucosa. High expression of Popdc3 protein was detected in 78 (25.49%) of 306 human gastric cancer cases, and low expression was detected in 228 (74.51%). Low expression of Popdc3 correlated with depth of invasion (P < 0.0001), regional lymph nodes (P < 0.0001) and distant metastasis (P = 0.02), and tumor, nodes, metastasis (TNM) stages (P < 0.0001). On multivariate analysis, only the patient's gender, regional lymph node metastasis, distant metastasis, TNM stages, and the expression of Popdc3 were independent prognostic factors in patients with gastric cancer. The Kaplan-Meier plot showed that low Popdc3 expression had a much more significant effect on the survival of those patients with early-stage tumors (χ² = 104.741, P < 0.0001), with a > 51.9% reduction in the three-year survival compared with high Popdc3 expression. In late stages, the difference was also significant (χ² = 5.930, P = 0.015), with a 32.6% reduction in the three-year survival.

CONCLUSION

Reduced expression of Popdc3 may play a significant role in the carcinogenesis and progression of gastric cancer. Popdc3 may be an independent prognostic factor.

Differentiating rectal carcinoma by an immunohistological analysis of carcinomas of pelvic organs based on the NCBI Literature Survey and the Human Protein Atlas database

The treatments and prognoses of pelvic organ carcinomas differ, depending on whether the primary tumor originated in the rectum, urinary bladder, prostate, ovary, or uterus; therefore, it is essential to diagnose pathologically the primary origin and stages of these tumors. To establish the panels of immunohistochemical markers for differential diagnosis, we reviewed 91 of the NCBI articles on these topics and found that the results correlated closely with those of the public protein database, the Human Protein Atlas. The results revealed the panels of immunohistochemical markers for the differential diagnosis of rectal adenocarcinoma, in which [+] designates positivity in rectal adenocarcinoma and [-] designates negativity in rectal adenocarcinoma: from bladder adenocarcinoma, CDX2[+], VIL1[+], KRT7[-], THBD[-] and UPK3A[-]; from prostate adenocarcinoma, CDX2[+], VIL1[+], CEACAM5[+], KLK3(PSA)[-], ACPP(PAP)[-] and SLC45A3(prostein)[-]; and from ovarian mucinous adenocarcinoma, CEACAM5[+], VIL1[+], CDX2[+], KRT7[-] and MUC5AC[-]. The panels of markers distinguishing ovarian serous adenocarcinoma, cervical carcinoma, and endometrial adenocarcinoma were also represented. Such a comprehensive review on the differential diagnosis of carcinomas of pelvic organs has not been reported before. Thus, much information has been accumulated in public databases to provide an invaluable resource for clinicians and researchers.

The novel monoclonal antibody HPC2 and N-cadherin distinguish pancreatic ductal adenocarcinoma from cholangiocarcinoma

Metastatic pancreatic ductal adenocarcinoma and primary cholangiocarcinoma are morphologically very similar and, therefore, challenging to distinguish in liver biopsies. The distinction is important because surgical management and prognosis differ significantly. Several immunohistochemical markers have been evaluated to aid this diagnosis, but aside from N-cadherin, which labels cholangiocarcinoma, few provide the combination of good sensitivity and specificity. Our laboratory recently developed the novel monoclonal antibody human pancreatic cancer fusion #2 (HPC2) that recognizes pancreatic cancer. We hypothesized that the combination of our new marker and N-cadherin can assist in distinguishing metastatic pancreatic cancer from cholangiocarcinoma. We immunostained resections of 60 pancreatic ductal adenocarcinomas and 31 cholangiocarcinomas for the HPC2 and N-cadherin antigens. We also stained 24 gallbladder adenocarcinomas, 11 ampullary adenocarcinomas, and 10 metastatic colonic adenocarcinomas to the liver. Sections were independently scored by 2 pathologists with good agreement using both markers (κ statistics, 0.62-0.64; P < .0001). HPC2 was observed in 80% of pancreatic cancers (48/60), 82% of ampullary (9/11), and 32% (10/31) of cholangiocarcinomas. N-cadherin stained 27% (16/60) of the pancreas cases and 58% (18/31) of the cholangiocarcinomas. Gallbladder and colon cancers were usually double negative (18/24 and 8/10, respectively). Each marker provided significant likelihood ratios to separate pancreatic cancer (HPC2, 2.48 [1.46-4.19]; P < .0001) from cholangiocarcinoma (N-cadherin, 2.17 [1.3-3.64]; P < .01). The combination of both markers provided even better specificity and positive likelihood ratios. We conclude that HPC2 and N-cadherin significantly improve accurate classification of pancreatic cancer and cholangiocarcinoma.

Proliferative and nonproliferative lesions of the rat and mouse hepatobiliary system

The INHAND Project (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP) and North America (STP) to develop an internationally-accepted nomenclature for proliferative and non-proliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature and differential diagnosis for classifying microscopic lesions observed in the hepatobiliary system of laboratory rats and mice, with color microphotographs illustrating examples of some lesions. The standardized nomenclature presented in this document is also available for society members electronically on the internet (http://goreni.org). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous and aging lesions as well as lesions induced by exposure to test materials. A widely accepted and utilized international harmonization of nomenclature for lesions of the hepatobiliary system in laboratory animals will decrease confusion among regulatory and scientific research organizations in different countries and provide a common language to increase and enrich international exchanges of information among toxicologists and pathologists.

Diagnosis of metastatic neoplasms: an immunohistochemical approach

CONTEXT

It is important to determine the type and/or site of origin of metastatic tumors for optimal clinical management.

OBJECTIVE

To summarize the use of currently available immunohistochemical markers in the evaluation of metastatic tumors.

DATA SOURCES

Review of relevant literature on immunohistochemical evaluation of tumors and the author's personal experience.

CONCLUSIONS

Immunohistochemistry is an important ancillary technique for evaluation of metastatic tumors and should be used in the context of routine morphology and clinical information. While a single marker may be used to support a known or suspected site of origin, a carefully constructed panel is strongly recommended, particularly for tumors of morphologically uncertain lineage or origin.

Hepatocellular carcinoma metastases to the epidural space

Hepatocellular carcinoma (HCC) is relatively uncommon in the United States, although hepatitis C, one of the known risk factors for disease, is currently showing burgeoning growth in the country. Hence, it is possible that the incidence of HCC also will increase. Clinicians and pathologists in the United States are relatively unfamiliar with the patterns of metastatic spread for HCC. We report 2 US-native patients with cirrhosis and HCC who developed epidural space metastasis, a pattern of disease spread seen infrequently, even in endemic areas. Diagnostic testing was delayed in both patients because of the lowered suspicion for metastasis and the fact that neither patient had recognized metastatic spread to more common sites, such as lung or lymph nodes. New-onset neck or back pain-especially with symptoms of paresthesia, radiculopathy, or cord compression-in the setting of HCC warrants prompt investigation for metastases to the spine and epidural space.

Pathologic evaluation of unknown primary cancer

The pathologic approach to metastases of unknown primary cancer (UPC) is stepwise and uses the clinical context, morphology, and, where necessary, immunohistochemistry (IHC). This review covers the initial approach to a UPC biopsy; the diagnosis of malignancy and broad tumor typing into carcinoma, melanoma, lymphoma, or sarcoma; and further subtyping of carcinoma into germ cell (broadly included), squamous, neuroendocrine, and solid organ including liver and renal, and adenocarcinomas. Finally, for adenocarcinoma, the prediction of primary tumor site, including lung, pancreas, stomach, colon, ovary, prostate, and breast, is discussed. For each tumor type, the morphologic features are presented alongside established useful IHC markers, with a description of their staining patterns and common diagnostic dilemmas. Optimal tissue handling and IHC interpretation, quality assurance, and limitations also are discussed. The target readership is oncologists, but other clinicians and trainee pathologists also may find the content of use.