Artifactual Cystic Spaces in Prostatic Transurethral Resections and Related Specimens: A Potential Diagnostic Confounder.

Aims. Histopathologic benign mimickers of prostate cancer have mostly focused on glandular mimics, with non-glandular mimics mainly limited to inflammatory conditions. While there is a paucity of literature recognizing small cystic (presumably artifactual) spaces in transurethral resection specimens, in some instances they can become florid enough to mimic vascular or epithelial neoplasms. Herein, we detailed histologic, immunophenotypic, and clinicopathologic findings in a large series of specimens showing prominent diagnostically confounding cystic spaces. Methods and Results. Sixty specimens were obtained (50 transurethral resections, 7 aquablations, 3 laser enucleations), from 17 different surgeons. Seven specimens had concurrent genitourinary pathology (4 prostatic adenocarcinoma, 1 solitary fibrous tumor, 1 prostatic atypia, 1 urothelial carcinoma in situ). The extent of cystic change among overall tissue examined ranged from 1 mm-8 mm (mean 3.4 mm), with luminal content of cystic spaces characterized as empty (72%), both empty and fluid-like (17%), and both empty and mucin-like (11%; mucin histochemical stain was negative on all specimens). Notable differences in degree of tissue cautery artifact or inflammation was not found. Immunohistochemistry performed on 30 specimens showed cystic spaces negative for S100, ERG, pankeratin, and CD45. Conclusion. Although artifactual in nature, in some instances small cystic spaces encountered in prostatic transurethral resections and more novel related procedures can become florid enough to warrant recognition as a potential diagnostic confounder of vascular or epithelial neoplasms.

New developments in existing WHO entities and evolving molecular concepts: The Genitourinary Pathology Society (GUPS) update on renal neoplasia.

The Genitourinary Pathology Society (GUPS) reviewed recent advances in renal neoplasia, particularly post-2016 World Health Organization (WHO) classification, to provide an update on existing entities, including diagnostic criteria, molecular correlates, and updated nomenclature. Key prognostic features for clear cell renal cell carcinoma (RCC) remain WHO/ISUP grade, AJCC/pTNM stage, coagulative necrosis, and rhabdoid and sarcomatoid differentiation. Accrual of subclonal genetic alterations in clear cell RCC including SETD2, PBRM1, BAP1, loss of chromosome 14q and 9p are associated with variable prognosis, patterns of metastasis, and vulnerability to therapies. Recent National Comprehensive Cancer Network (NCCN) guidelines increasingly adopt immunotherapeutic agents in advanced RCC, including RCC with rhabdoid and sarcomatoid changes. Papillary RCC subtyping is no longer recommended, as WHO/ISUP grade and tumor architecture better predict outcome. New papillary RCC variants/patterns include biphasic, solid, Warthin-like, and papillary renal neoplasm with reverse polarity. For tumors with 'borderline' features between oncocytoma and chromophobe RCC, a term "oncocytic renal neoplasm of low malignant potential, not further classified" is proposed. Clear cell papillary RCC may warrant reclassification as a tumor of low malignant potential. Tubulocystic RCC should only be diagnosed when morphologically pure. MiTF family translocation RCCs exhibit varied morphologic patterns and fusion partners. TFEB-amplified RCC occurs in older patients and is associated with more aggressive behavior. Acquired cystic disease (ACD) RCC-like cysts are likely precursors of ACD-RCC. The diagnosis of renal medullary carcinoma requires a negative SMARCB1 (INI-1) expression and sickle cell trait/disease. Mucinous tubular and spindle cell carcinoma (MTSCC) can be distinguished from papillary RCC with overlapping morphology by losses of chromosomes 1, 4, 6, 8, 9, 13, 14, 15, and 22. MTSCC with adverse histologic features shows frequent CDKN2A/2B (9p) deletions. BRAF mutations unify the metanephric family of tumors. The term "fumarate hydratase deficient RCC" ("FH-deficient RCC") is preferred over "hereditary leiomyomatosis and RCC syndrome-associated RCC". A low threshold for FH, 2SC, and SDHB immunohistochemistry is recommended in difficult to classify RCCs, particularly those with eosinophilic morphology, occurring in younger patients. Current evidence does not support existence of a unique tumor subtype occurring after chemotherapy/radiation in early childhood.