Mutated ASXL1 upregulates mTOR expression in renal cell carcinoma with fibromyomatous stroma

Renal cell carcinoma with fibromyomatous stroma (RCC FMS), defined as an emerging entity in the 2016 WHO classification and recommended to be a novel entity by GUPS, is represented by tumor cells with clear to mildly eosinophilic cytoplasm displaying elongated and branching tubules and papillae. A fibromyomatous stroma could be observed in these tumors. These tumors are immunopositive for CK7 and featured by ELOC and/or TSC/mTOR gene mutations. In the 2022 WHO classification, ELOC mutated RCC is classified as a molecularly defined RCCs as an individual renal entity. However, there are limited descriptions of TSC/mTOR alterations in RCC FMS. Herein, we reported a case of 28-year-old woman with RCC FMS with intact ELOC and TSC/mTOR genes but ASXL1 mutation. The tumor cells were positive for mTOR expression. This case may indicate that altered mTOR expression, but not limited to mutated TSC/mTOR gene, that participates in the pathogenesis of RCC FMS.

Automated summary

Renal cell carcinoma with fibromyomatous stroma (RCC FMS) is a unique type of kidney cancer characterized by the presence of a fibromyomatous stroma. This study presented a case of RCC FMS in a 28-year-old woman, which showed distinct gene mutations and suggested the involvement of altered mTOR expression in the pathogenesis of this tumor.