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BACKGROUND: TCEB1-mutant renal cell carcinoma (RCC) is a rare variant of RCC with clear-cell features. Owing to its unique morphological and molecular features it has recently been proposed as a separate entity. Initial series suggested an indolent, early-stage phenotype. Here we expand our clinical cohort and describe a more detailed genomic analysis looking for potential drivers of aggressiveness. DESIGN, SETTING, AND PARTICIPANTS: We identified five new cases in our institutional sequencing cohort, four of whom were found to have high-stage disease (American Joint Committee on Cancer stage III/IV). Twelve previously reported cases were pooled for comparison purposes (Sato, The Cancer Genome Atlas, TRACERx Renal). OUTCOME MEASURES AND STATISTICAL ANALYSIS: We used our previously validated pipeline to analyze somatic mutations and copy number alterations (CNAs) in seven tumor samples with available data and estimated the number of cancer cells bearing each somatic mutation. The oncogenic potential of mutations was assessed using OncoKB and two other algorithms. Mann-Whitney U tests were used to evaluate differences in genomic markers between stage groups. RESULTS AND LIMITATIONS: All tumors showed biallelic inactivation of the TCEB1 gene according to a combination of somatic mutation and CNA analyses. Mutations were always found in residues involved in hydrophobic interactions with VHL. We found that high-stage tumors had additional oncogenic mutations (median 1, interquartile range [IQR] 1-1 vs 2, IQR 2-2; median difference 1, 95% confidence interval [CI] 1-1; p= 0.002) and showed whole-genome doubling events. They also seemed to have a higher burden of somatic CNAs (median fraction CNA genome 0.10, IQR 0.10-0.15 vs 0.63, IQR 0.58-0.68), however, this finding did not reach statistical significance (median difference 0.49, 95% CI 0.33-0.63; p=0.052). CONCLUSIONS: TCEB1-mutant RCC can show variable behavior ranging from very indolent to aggressive. Specific molecula

BACKGROUND: Clear cell papillary renal cell carcinoma (CCPRCC) is a recently described tumor entity. Several questions remain about its epidemiology, molecular features, and clinical behavior. OBJECTIVE: To comprehensively evaluate clinicopathologic and molecular features of CCPRCC, and compare it with more common kidney cancer subtypes. DESIGN, SETTING, AND PARTICIPANTS: We identified 89 CCPRCC patients and compared their clinicopathologic features with 1120 localized clear cell renal cell carcinoma (ccRCC) and 129 type 1 papillary renal cell carcinoma (pRCC) patients. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: Nonparametric statistical testing was used to compare relevant features between tumor types. Overall, cancer-specific survival (CSS) and metastasis-free survival estimates were calculated from initial diagnosis using the Kaplan-Meier method. Patients with ipsilateral multifocal disease were explored further. A subset of CCPRCC tumors underwent genomic analysis and were compared with other RCC subtypes. RESULTS AND LIMITATIONS: A higher proportion of female (45% vs 32%) and African-American (19% vs 3%) patients were observed in the CCPRCC cohort than in the ccRCC and pRCC cohorts. CCPRCC tumors also had increased odds of presenting with additional ipsilateral masses (odds ratio [OR]: 4.41 [confidence interval {CI}: 2.34, 8.15], p < 0.001) and bilateral disease (OR: 4.80 [CI: 2.40, 9.59], p < 0.001) compared with ccRCC tumors. On molecular analysis, CCPRCC tumors showed fewer somatic aberrations and a greater degree of mitochondrial DNA depletion. In multifocal CCPRCC tumors, histologic concordance among the different renal cell carcinoma masses was estimated at 44% (7/16), and none of the individuals presenting exclusively with CCPRCC tumors developed metastatic disease after 5 yr. In contrast, multifocal tumors with CCPRCC and other nonconcordant histologies were more likely to experience adverse outcomes (CSS, log rank p = 0.034). CONCLUSIONS: CCPRCC is