[Eosinophilic, solid, and cystic renal cell carcinoma (ESC-RCC)].

Despite its descriptive name, eosinophilic, solid, and cystic renal cell carcinoma (ESC-RCC) represents a distinctive epithelial renal tumor entity defined by characteristic clinicopathological and molecular features. ESC-RCC occurs predominantly in women and is characterized in the majority of cases by sporadic (somatic) TSC mutations. A small subset of cases, however, affects patients with TSC germline mutations (tuberous sclerosis syndrome). TSC mutations have therefore been shown to be pathogenetic in this type of tumor. Most tumors present as small (pT1) well circumscribed but not encapsulated lesions with variable macrocystic spaces on their cut surface. Immunohistochemically, their CD117-/CK7-/CK20+ profile is characteristic. Although the tumor cell nuclei of the ESC-RCC occasionally correspond to ISUP/WHO grade 2-3, these tumors are essentially indolent with aggressive cases being only rarely observed. Single case reports have documented effective treatment of aggressive cases with mTOR inhibitors. ESC-RCC needs to be distinguished from a variety of eosinophilic RCC types with secondary cystic changes including cystic SDH-deficient RCC, the recently proposed eosinophilic vacuolated tumor (EVT; also mTOR-related), oncocytoma, and low-grade oncocytic tumor (LOT). The generally indolent behavior and frequent TSC/mTOR alterations in ESC-RCC, EVT, and some LOTs raise the question of whether these lesions represent independent tumor entities or are merely morphological variants on the spectrum of eosinophilic low-grade TSC/mTOR-related neoplasms.