The Application and Pitfalls of Immunohistochemical Markers in Challenging Diagnosis of Genitourinary Pathology

CONTEXT.—

The morphologic features of different entities in genitourinary pathology overlap, presenting a diagnostic challenge, especially when diagnostic materials are limited. Immunohistochemical markers are valuable when morphologic features alone are insufficient for definitive diagnosis. The World Health Organization classification of urinary and male genital tumors has been updated for 2022. An updated review of immunohistochemical markers for newly classified genitourinary neoplasms and their differential diagnosis is needed.

OBJECTIVE.—

To review immunohistochemical markers used in the diagnosis of genitourinary lesions in the kidney, bladder, prostate, and testis. We particularly emphasized difficult differential diagnosis and pitfalls in immunohistochemistry application and interpretation. New markers and new entities in the 2022 World Health Organization classifications of genitourinary tumors are reviewed. Recommended staining panels for commonly encountered difficult differential diagnoses and potential pitfalls are discussed.

DATA SOURCES.—

Review of current literature and our own experience.

CONCLUSIONS.—

Immunohistochemistry is a valuable tool in the diagnosis of problematic lesions of the genitourinary tract. However, the immunostains must be carefully interpreted in the context of morphologic findings with a thorough knowledge of pitfalls and limitations.

Yolk Sac Tumor Originating From Cervical Adenocarcinoma: A Case Predominated by Enteroblastic Differentiation

The fetal gut-like phenotype can be found in yolk sac tumors and adenocarcinomas with enteroblastic differentiation (AEBDs). We report a cervical yolk sac tumor in a 44-yr-old woman. The tumor has similar morphology, immunophenotype, and molecular features to the AEBD of the digestive system. The tumor showed a glandular-predominant growth pattern, composed of columnar cells with clear glycogen-rich cytoplasm. The microcystic/reticular architecture or Schiller-Duval bodies were not found in the tumor. Immunohistochemically, the tumor cells were positive for p16, glypican-3 (GPC3), spalt-like transcription factor 4 (SALL4), CDX-2, and p53. TP53 mutation was identified by next-generation sequencing, and human papillomavirus (HPV) 35 was detected by HPV DNA polymerase chain reaction. In the present case, the adenocarcinoma cells in the superficial cervical glandular epithelium and the nonclear glandular components proved the existence of somatic components. The positivity of p16 and HPV also supports that the present case originates from an HPV-associated adenocarcinoma. The yolk sac tumor should be thought of as "germ cell differentiation" from a somatic carcinoma. This kind of yolk sac tumor arising from somatic-type adenocarcinoma in the female genital tract may be the counterpart of AEBD in the digestive tracts and adenocarcinomas with fetal gut-like morphology in other organs. The tumor might be more aggressive than conventional adenocarcinoma, pathologists should highlight the existence of the enteroblastic component in the pathologic report.

Practical Application of Lineage-Specific Immunohistochemistry Markers: Transcription Factors (Sometimes) Behaving Badly

CONTEXT.—

Transcription factors (TFs) are proteins that regulate gene expression and control RNA transcription from DNA. Lineage-specific TFs have increasingly been used by pathologists to determine tumor lineage, especially in the setting of metastatic tumors of unknown primary, among other uses. With experience gathered from its daily application and increasing pitfalls reported from immunohistochemical studies, these often-touted highly specific TFs are not as reliable as once thought.

OBJECTIVES.—

To summarize the established roles of many of the commonly used TFs in clinical practice and to discuss known and potential sources for error (eg, false-positivity from cross-reactivity, aberrant, and overlap "lineage-specific" expression) in their application and interpretation.

DATA SOURCES.—

Literature review and the authors' personal practice experience were used. Several examples selected from the University Health Network (Toronto, Ontario, Canada) are illustrated.

CONCLUSIONS.—

The application of TF diagnostic immunohistochemistry has enabled pathologists to better assess the lineage/origin of primary and metastatic tumors. However, the awareness of potential pitfalls is essential to avoid misdiagnosis.

Immunohistochemical Pitfalls in Genitourinary Pathology: 2018 Update

Immunohistochemistry may be a very useful adjunct to morphologic diagnosis in many areas of surgical pathology, including genitourinary pathology. In this review, we address common diagnostic dilemmas where immunophenotypic analysis may be utilized and we highlight pitfalls specific to each scenario. For prostate, we review the diagnosis of limited prostatic adenocarcinoma and the distinction of high-grade prostatic adenocarcinoma from urothelial carcinoma. We also cover markers of urothelial lineage in the diagnosis of metastatic carcinoma of unknown primary site. In the kidney, distinction of poorly differentiated renal cell carcinoma from urothelial carcinoma and epithelioid angiomyolipoma, adjuncts to the recognition of hereditary renal neoplasia, and the diagnosis of metastatic renal cell carcinoma are discussed. Finally, for testis we address distinction of germ cell tumors from sex cord-stromal tumors, as well as the diagnosis of metastatic germ cell tumors.

SALL4 suppresses PTEN expression to promote glioma cell proliferation via PI3K/AKT signaling pathway

Spalt-like transcription factor 4 (SALL4), a oncogene, is known to participate in multiple carcinomas, and is up-regulated in glioma. However, its actual role and underlying mechanisms in the development of glioma remain unclear. The present study explored the molecular functions of SALL4 in promoting cell proliferation in glioma. The expression level of SALL4 in 69 human glioma samples and six non-tumor brain tissues was determined using real-time polymerase chain reaction (PCR). Then, we transfected U87 and U251 cell lines with siRNA, and assessed cellular proliferation and cell cycle to understand the function of SALL4, and the relationship between SALL4, PTEN and PI3K/AKT pathway. PCR confirmed that the expression of SALL4 was higher in the glioma samples than non-tumor brain tissues. Cellular growth and proliferation were dramatically reduced following inhibition of SALL4 expression. Western blot showed increase in PTEN expression when SALL4 was silenced, which in turn depressed the activation of PI3K/AKT pathway, suggesting that PTEN was a downstream target of SALL4 in glioma development. Therefore, SALL4 could act as a proto-oncogene by regulating the PTEN/PI3K/AKT signaling pathway, thereby facilitating proliferation of glioma cells.

A case of adenocarcinoma with enteroblastic differentiation of the ampulla of Vater

Cancer of the ampulla of Vater is rare, though it has various histological types and its histogenesis is fascinating in view of the anatomically complex nature of the ampulla. Fetal gut-like adenocarcinoma, usually found in the stomach, can also develop in the ampullary region in extremely rare cases. Here we present a case of ampullary adenocarcinoma with enteroblastic and neuroendocrine differentiation. A 55-year-old woman presented with an epigastric pain. Endoscopic examination revealed a 2-cm submucosal tumor-like lesion in the ampulla. The surgical specimen showed that an exposed protruding type of tumor appeared as a well-demarcated whitish-yellow solid mass. Microscopically, the tumor had proliferated in the common channel and invaded the duodenal submucosa with mucosal lesion of intestinal-type adenocarcinoma. The main tumor consisted of three different histological types showing transitional areas: adenocarcinoma with enteroblastic differentiation (ENT), neuroendocrine carcinoma (NEC), and well differentiated adenocarcinoma (WEL). Morphologically the ENT resembled fetal gut and immunohistochemically expressed SALL4 and glypican 3. The WEL was positive for CK20 and CDX2, revealing an intestinal-type phenotype. AFP and HepPar1 were not evident in any part of the lesion. We speculated this tumor had arisen from intestinal-type adenocarcinoma of the common channel and acquired enteroblastic and neuroendocrine differentiation during growth.