Comprehensive genomic profiling (CGP) of chromophobe renal cell carcinoma (chrRCC) compared with clear cell RCC (ccRCC): Impact of FLCN genomic alteration (GA) status.

Abstract

292 Background: FLCN is a tumor suppressor gene associated with cutaneous hair follicle development. FLCN germline mutations are linked to inherited chrRCC in the Birt-Hogg-Dube (BHD) syndrome. We queried whether clinically sporadic chrRCC featured FLCN mutations by comparing the genomic profiles of chrRCC with ccRCC. Methods: 108 chrRCC and 2110 ccRCC underwent hybrid-capture based comprehensive genomic profiling (CGP) to evaluate all classes of genomic alterations (GA). Tumor mutational burden (TMB) was determined on up to 1.1 Mbp of sequenced DNA and microsatellite instability (MSI) was determined on 114 loci. PD-L1 expression was determined by IHC (Dako 22C3). Results: Patients (pts) with chrRCC were more frequently female and younger than pts with ccRCC p <.0001). None of the submitted clinical records in the chrRCC cases listed signs of BHD syndrome. FLCN GA were identified in only 2.3% of the ccRCC cases with 37% of the GA predicted to be germline. chrRCC did not reveal somatic or germline FLCN GA. GA/tumor were slightly higher in ccRCC vs chrRCC (3.6 vs 2.4; NS). GA more frequent in chrRCC included TP53, RB1 and PTEN. GA more frequent in the ccRCC included VHL, BAP1, PBRM1, SETD2, CDKN2A/B, ARID1A, NF2, PIK3CA and TERT. Putative biomarkers of immune checkpoint inhibitor (ICPI) response were infrequent in both groups with only a slightly higher, but still low, mean TMB in ccRCC vs chrRCC cases. IHC revealed moderate PD-L1 expression at low and minimal PD-L1 expression at high staining level, which was slightly increased in the chrRCC group. Conclusions: FLCN mutations that are associated with the familial incidence of chrRCC were not associated with sporadic chrRCC. Sporadic chrRCC has substantially different genomic profile from ccRCC and may harbor a few ‘targetable’ GA. The prediction of response to ICPI in RCC remains challenging with chrRCC featuring slightly higher PD-L1 expression and ccRCC featuring higher PBRM1 GA and higher TMB.[Table: see text]