Variability in endometrial carcinoma pathology practice: opportunities for improvement with molecular classification.

We assessed the landscape of diagnostic pathology practice and how molecular classification could potentially impact management of patients with endometrial cancer by collecting patient samples, clinicopathologic data, and patient outcomes from EC patients diagnosed in 2016 at 10 Canadian tertiary cancer centers and 19 community hospitals. ProMisE molecular subtype (POLEmut, MMRd, p53abn, No Specific Molecular Profile (NSMP)) was assigned retrospectively. 1357 patients were fully evaluable including 85 POLEmut (6.3%), 380 MMRd (28.0%), 643 NSMP (47.4%), and 249 p53abn ECs (18.3%). Immunohistochemistry (IHC) for MMR proteins was undertaken at the time of primary diagnosis in 2016 in only 42% of the cohort (570/1357; range 3.5-95.4%/center). p53 IHC had only been performed in 21.1% of the cohort (286/1357; range 10.1-41.9%/center). Thus, based on the retrospective molecular subtype assignment, 54.7% (208/380) of MMRd EC had not been tested with MMR IHC (or MSI) and 48.2% (120/249) of p53abn ECs were not tested with p53 IHC in 2016. Molecular subtype diversity within histotypes was profound; most serous carcinomas were p53abn (91.4%), but only 129/249 (51.8%) p53abn EC were serous. Low-grade (Gr1-2) endometrioid carcinomas were mostly NSMP (589/954, 61.7%) but included all molecular subtypes, including p53abn (19/954, 2.0%). Molecular subtype was significantly associated with clinical outcomes (p < 0.001) even in patients with stage I disease (OS p = 0.006, DSS p < 0.001, PFS p < 0.001). Assessment of national pathologic practice in 2016 shows highly variable use of MMR and p53 IHC and demonstrates significant opportunities to improve and standardize biomarker reporting. Inconsistent, non-reflexive IHC resulted in missed opportunities for Hereditary Cancer Program referral and Lynch Syndrome diagnosis, and missed potential therapeutic implications (e.g., chemotherapy in p53abn EC, immune blockade for MMRd EC). Routine integration of molecular subtyping into practice can improve the consistency of EC pathology assessment and classification.

Oncocytic renal cell carcinoma with immunohistochemical properties of renal oncocytoma.

Renal oncocytoma (RO) is a characteristic benign renal tumor. The existence of malignant RO is controversial and anecdotal, partly due to a lack of specific markers for RO. With recent advances in immunohistochemistry, RO can be distinguished from other renal neoplasms with routine stains and with the aid of immunostaining. We report two cases of renal neoplasms with similar histopathological appearances. They were characterized by oncocytic cytoplasm, numerous intra-cytoplasmic vacuoles, uniform round to oval hyperchromatic nuclei with remarkably thick nuclear membranes and prominent nucleoli. The tumor cells were closely packed and disposed in an alveolar pattern. The neoplastic cells were diffusely reactive for CD117 and progesterone receptor, and diffusely or focally reactive for cytokeratin AE1/AE3, and focally reactive for cytokeratin 7, CD10, and racemase. The cells were non-reactive for renal cell carcinoma (RCC) antigen, vimentin, S100, and neuroendocrine markers. One tumor showed lymph node metastasis. Due to the remarkable cytological atypia, lymph node metastasis, and similar immunological features of RO, these two tumors likely represent a distinct subtype of RCC related to RO.