Renal cell carcinoma with leiomyomatous stroma: a review of an emerging entity distinct from clear cell conventional renal cell carcinoma.

Clear cell renal cell carcinomas accounts for 65 to 75% of all malignant renal tumors. The International Society of Urological Pathology 2012 Vancouver Classification of renal neoplasia and the World Health Organization 2016 Classification of renal tumors have included renal cell carcinoma with leiomyomatous stroma in a category of emerging/provisional entities of renal cell carcinoma. Macroscopically, renal cell carcinomas with leiomyomatous stroma are well circumscribed tumors with a cut surface of gray-white fibrotic tissues. Microscopically, the tumors are composed of nodules and anastomosing tubules of renal cells with clear cytoplasms. The carcinoma cells are embedded in a cellular stroma composed of intertwining bundles of smooth muscle. Immunohistochemically, the neoplastic cells are typically positive for CK7 and CD10 immunomarkers. Biomarkers including CAIX, pankeratin, vimentin, and HIF1-alpha stain positively in many renal cell carcinomas with leiomymomatous stroma. Molecular genetic studies of this variant of tumor reveal no VHL mutation, trisomy 7 or trisomy 17. However, a TCEB1 mutation has been demonstrated in a subset of tumors and rare cases are reported from patients with a family history of tuberous sclerosis. The biological behavior of this variant of tumor is indolent and the prognosis is favorable.