Histologic diversity in chromophobe renal cell carcinoma does not impact survival outcome: A comparative international multi-institutional study

Cystic Features in Renal Epithelial Neoplasms and Their Increasing Clinical and Pathologic Significance

Most cystic renal tumors after resection (Boniak IIF to IV cysts) have an indolent course despite the significantly higher proportion of malignant [ie, renal cell carcinoma (RCC)] diagnosis. Most cystic renal tumors have clear cell histology that include cystic clear cell RCC and multilocular cystic renal neoplasm of low malignant potential (MCNLMP). There is growing evidence to suggest that MCNLMP, cystic clear cell RCC, and noncystic clear cell RCC form a cystic-to-solid biological spectrum with MCNLMP representing the most indolent form and with cystic clear cell RCC behaving better than noncystic (solid) clear cell RCC. Extensively (>75%) cystic clear cell RCC also has an excellent outcome similar to MCNLMP stressing the need to reevaluate the histologic criteria that separate these 2 cystic clear cell tumors. Other tumors with clear cells that can be extensively cystic such as the recently reclassified noncancerous clear cell papillary renal tumor and the newly described MED15::TFE3 RCC also have indolent course and may mimic MCNLMP. Cystic features occur also in renal tumors with nonclear cell histology including tumors capable of metastasis such as acquired cystic disease-associated, tubulocystic, fumarate hydratase-deficient, and eosinophilic solid and cystic RCCs. Cystic imaging presentation of some renal tumors such as papillary RCC can be attributed in part to pseudocystic necrosis and hemorrhage. It is important to know that tubulocystic RCC may have a lower Bosniak class presentation that overlaps with benign renal cysts (Bosniak I to IIF) that are managed conservatively. This review highlights the cystic renal tumors with clear cell and nonclear cell morphologies including some novel RCC subtypes that may have cystic features. The presence of cystic features and their extent may aid in the classification and prognostication of renal neoplasms underscoring its increasing importance in the pathologic diagnosis and reporting of renal neoplasia.

High-Grade, Nonsarcomatoid Chromophobe Renal Cell Carcinoma: A Series of 22 Cases With Novel Molecular Features on a Subset

Chromophobe renal cell carcinoma (ChRCC) is the third most common subtype of renal cell carcinoma and typically exhibits indolent behavior, though a rare subset can exhibit high-grade morphologic features and is associated with a poor prognosis. Although there are limited data on the molecular characteristics of metastatic and sarcomatoid ChRCC, the molecular features of high-grade, nonsarcomatoid ChRCC remain unexplored. Herein, we characterize 22 cases of ChRCC with high-grade, nonsarcomatoid components. High-grade ChRCC frequently demonstrated advanced stage at diagnosis (64% ≥pT3a or N1), with regions of extrarenal extension, nodal metastases, and vascular invasion consisting solely of high-grade ChRCC morphologically. We performed spatially guided panel-based DNA sequencing on 11 cases comparing high-grade and low-grade regions (n = 22 samples). We identified recurring somatic alterations emblematic of ChRCC, including deletions of chromosomes 1, 2, 6, 10, 13, 17, and 21 in 91% (10/11) of cases and recurring mutations in TP53 (81.8%, n = 9/11) and PTEN (36.4%, n = 4/11). Notably, although PTEN and TP53 alterations were found in both high-grade and low-grade regions, private mutations were identified in 3 cases, indicating convergent evolution. Finally, we identified recurring RB1 mutations in 27% (n = 3) of high-grade regions leading to selective protein loss by immunohistochemistry not observed in adjacent low-grade regions. This finding was confirmed in The Cancer Genome Atlas cohort where 2 of 66 cases contained RB1 mutations and demonstrated unequivocal high-grade, nonsarcomatoid morphology. We also detected multiple chromosomal gains confined to the high-grade regions, consistent with imbalanced chromosome duplication. These findings broaden our understanding of the molecular pathogenesis of ChRCC and suggest that subclonal RB1 mutations can drive the evolution to high-grade, nonsarcomatoid ChRCC.

Chromophobe Renal Cell Carcinoma With Extensive Retraction Artifact: A Potential Diagnostic Pitfall From Micropapillary Urothelial Carcinoma

In addition to "classic" and eosinophilic subtype, chromophobe renal cell carcinoma (RCC) is well-known to demonstrate various morphological patterns including adenomatoid, microcystic, pigmented, multicystic, papillary, neuroendocrine-like, and small cell-like, all of which are important to appreciate for accurate diagnosis. Herein, we expand on a unique chromophobe RCC morphology not previously described consisting of tumor cells with extensive stromal retraction, mimicking upper urothelial tract micropapillary carcinoma (MPC). Twelve MPC-like chromophobe RCC nephrectomies were reviewed with clinicopathological features recorded; molecular testing was performed on 7 of 12 tumors. Patients were mostly men (n=10) with a mean age of 65 years. Mean tumor size was 6.4 cm with pathological stage distribution as follows: 4 (33%) T1a, 2 (17%) T1b, 1 (8%) T2b, and 3 (25%) T3a. The extent of MPC-like chromophobe RCC foci ranged from 10% to 40% (mean=26%; there was no correlation between the extent of MPC-like chromophobe RCC foci and tumor stage). Other chromophobe RCC morphological patterns were not identified. When performed, all (100%) tumors depicted prototypic chromophobe RCC staining pattern of KIT positivity/KRT7 positivity. Molecular showed 6 of 7 (86%) with multiple chromosomal losses. Clinically significant mutations were identified in NF1, TP53, FLCN (likely somatic), CHEK2, and ZFHX3 genes. Follow up available in 9 patients showed no evidence of disease (mean=23 months). Although the etiology behind the extensive stromal retraction in our tumors is unknown, this may likely be artifactual in nature. Nonetheless, it is important to include MPC-like chromophobe RCC in the spectrum of "variant" morphologies to avoid diagnostic pitfalls from micropapillary carcinoma.

Renal Neoplasia Occurring in Patients With PTEN Hamartoma Tumor Syndrome : Clinicopathologic Study of 12 Renal Cell Carcinomas From 9 Patients and Association With Intrarenal "Lipomas"

The aim of this study was to assess the histopathologic spectrum of renal tumors in patients with PTEN hamartoma tumor syndrome (PHTS), with a specific focus on potential features predictive of the underlying syndrome. A multi-institutional study was conducted to obtain clinical and pathologic data on renal tumors arising in patients with PHTS, either diagnosed by germline mutational analysis or clinical criteria for Cowden syndrome. Histologic sections of the renal tumors were re-reviewed for classification. Twelve renal epithelial tumors from 9 patients were identified (4 males and 5 females, with a mean age of 41.8 y), 7 of whom carried germline PTEN mutations. All 12 renal epithelial tumors were renal cell carcinomas (RCCs): 5 were chromophobe RCCs, 4 papillary RCCs, and 3 RCC not otherwise specified. Pathologic stage distribution was: 7 (59%) pT1a, 2 (17%) pT1b, 1 (8%) pT2a, 1 (8%) pT2b, and 1 (8%) pT3a. World Health Organization/International Society of Urological Pathology (WHO/ISUP) histologic grade was applicable in 7 (54%) nonchromophobe tumors: 4 (57%) G2, 2 (29%) G3, and 1 (14%) G4. An unexpected histologic finding was the presence of 2 patients with incidental microscopic collections of intrarenal adipocytes that had no features of angiomyolipoma (and were negative with 2 sensitive PEComa markers: cathepsin-K and GPNMB); both were classified as lipoma/"lipomatous hamartomas." The average follow-up interval was 67.8 months (13 to 172 mo): 5 patients had no evidence of disease, 2 were lost to follow-up, 1 died of other (non-PHTS) causes (ie, prostate cancer), and 1 was alive with metastatic RCC to the lung (RCC not otherwise specified with rhabdoid differentiation). All tumors showed loss of nuclear PTEN staining by immunohistochemistry. Fumarate hydratase was retained and 2SC was negative in all papillary RCCs. CK7 was moderate-strong/diffuse positive in 4 of 5 chromophobe RCCs and in 3 of 4 papillary RCCs. Renal epithelial tumors associated with PHTS represent a heterogeneous group of RCCs, but classic chromophobe and papillary RCC are most common. The majority have a favorable clinical behavior as would be predicted by subtype. In contrast to other hereditary renal neoplasia syndromes, morphologic features of the RCCs do not allow identification of PHTS-associated neoplasia with any degree of specificity in the absence of clinical setting and/or prior history, but the presence of microscopic "lipomas" within the kidney may provide a clue in rare cases. Therefore, clinical suspicion and genetic counseling with germline testing remain necessary for identifying PHTS-associated RCC.

Algorithm-Based Approach to the Histological Routine Diagnosis of Renal Oncocytic Tumors in Core Biopsy Specimens

PURPOSE OF REVIEW

A growing number of tumor entities with badly defined limits are enlarging in the last years the family of oncocytic tumors in the kidney.

RECENT FINDINGS

Chromophobe renal cell carcinoma (ChRCC) and renal oncocytoma (RO) are classically well-known tumors, but the borderland between them, and their precise connection, remains a matter of debate. Aside from that, other emerging and provisional entities, like eosinophilic solid and cystic renal cell carcinoma (ESC RCC), eosinophilic vacuolated tumor (EVT), low-grade oncocytic tumor (LOT), and papillary renal neoplasm with reverse polarity (PRRP), have been recently described. This spectrum of tumors remains a diagnostic challenge in renal pathology, especially if the specimen obtained is scarce. This review focuses on practical diagnostic problems when managing core biopsies and proposes a diagnostic algorithm maximizing the information provided by both morphology and immunohistochemistry. So, a combination of morphologic features on hematoxylin-eosin and six antibodies (CK7, CD117, CK20, CD10, GATA-3, and cathepsin K) is advised to be used in a stepwise fashion.