Immunohistochemical characterization of renal tumors in patients with Birt-Hogg-Dubé syndrome.

Birt-Hogg-Dubé syndrome (BHD) is an autosomal dominant disorder associated with a germline mutation of folliculin (FLCN). The affected families are at a high risk for developing multiple renal cell carcinomas (RCC). Little is known about the immunostaining patterns of mutant FLCN-associated RCCs. We investigated 32 RCCs obtained from 17 BHD patients. The studied tumors included chromophobe RCCs (n = 15), hybrid oncocytic/chromophobe tumors (HOCT) (n = 14) and clear cell RCCs (n = 3). Almost all chromophobe RCCs and HOCTs revealed positive staining for S100A1, Ksp-cadherin and CD82. They stained either focally or diffusely for CK7, and were negative for CA-IX. All clear cell RCCs were positively stained for CA-IX and negative for CK7. These data confirmed that mutant FLCN-associated oncocytic and clear cell RCCs exhibited generally similar immunostaining patterns compared to their sporadic counterparts. Frequent positive staining for S100A1, Ksp-cadherin and CD82 in chromophobe RCCs and HOCTs indicated that these two types were relatively similar rather than distinctively different in their patterns of immunoreactivity. Characteristic peri-nuclear halos and polygonal cells with clear cytoplasm, which often misleads pathologists into the diagnosis of clear cell RCC, should be carefully examined using an immunohistochemical panel including CA-IX, Ksp-cadherin, CD82 and CK7.