Heterozygous germline FLCN mutation in Birt-Hogg-Dubé syndrome with bilateral renal hybrid oncocytic/chromophobe tumor and unilateral renal chromophobe cell carcinoma: a case report

Birt-Hogg-Dubé syndrome in an overall view: Focus on the clinicopathological prospects in renal tumors

Birt-Hogg-Dubé syndrome (BHD) represents a rare autosomal dominant tumor predisposition syndrome characterized by skin lesions, lung cysts, and renal tumors. The predominant histological subtypes of BHD-related renal tumors include hybrid oncocytoma-chromophobe tumors, oncocytomas, and chromophobe renal cell carcinomas, all exhibiting eosinophilic/oncocytic features. Immunohistochemistry staining for KIT (CD117) and CK7 exhibits variability in these tumor types. Germline mutations in FLCN have been consistently identified. Generally, patients with BHD demonstrate a favorable prognosis with minimal metastatic potential. Nonetheless, the comprehensive elucidation of pathological characteristics of BHD remains incomplete, particularly in BHD-associated renal tumors that deviate from the previously identified subtypes, thereby complicating the differential diagnosis. In this review, we provide a comprehensive overview of BHD encompassing epidemiology, clinical manifestations, genetic and molecular pathogenesis, as well as clinical diagnostic modalities. Emphasis is placed on clinicopathological features, specifically focusing on BHD-associated renal tumors. Collectively, this review aims to present the latest insights into BHD which benefits in the early detection, therapeutic decision-making, and prognosis prediction in BHD cases, and deepen the understanding of sporadic renal tumors.