Renal Cell Carcinoma With Hemangioblastoma-Like Features, Fibromyomatous Stroma, and TSC1 Mutation

Renal cell carcinoma (RCC) with fibromyomatous stroma (RCC-FMS) was classified as an "emerging/provisional" entity in the 2016 WHO classification of tumors, specifically categorized as RCC with (vascular) fibromyomatous stroma. However, it was not included in the 2022 WHO classification. Renal cell carcinoma with hemangioblastoma (RCC-HB)-like features has also been reported infrequently in recent years. RCC-HB-like features and fibromyomatous stroma is quite rare, with only two reports in the literature. This report describes a rare tumor of RCC-HB-like features and fibromyomatous stroma associated with TSC1 mutations. A female patient was incidentally discovered a right renal mass during a routine physical examination conducted 2 weeks prior. Histology revealed that the tumor consisted of three distinct components: clear cell papillary renal cell tumor (CCPRCT)-like areas, fibromyomatous stroma, and HB-like areas. Immunohistochemical staining showed that the CCPRCT-like components exhibited basolateral, cup-shaped CAIX staining and were diffusely positive for AE1/AE3, CK7, and PAX-8, partially positive for AMACR/P504S, and weakly positive for CD10. The fibromyomatous stroma was positive for H-caldesmon, desmin, and SMA. In the HB-like components, α-inhibin, ERG, CD34, CAIX, and vimentin were all diffusely positive, CD10 was partially positive, and PAX-8 showed scattered, weak positivity. Whether RCC-HB features and fibromyomatous stroma can be regarded as a distinct subtype of RCC remains to be discussed by accumulation of more cases.