Tubulocystic renal cell carcinoma

Tubulocystic renal cell carcinomas are a rare subtype of renal cell carcinoma (RCC) with predominantly cystic appearance.

Terminology

Tubulocystic renal cell carcinoma was first identified as a distinct histopathologic entity in 2005, and subsequently acknowledged as an independent disease category in the 2016 WHO classification of renal tumors ^1,3.

Epidemiology

Peak incidence occurs in the 6^th through 8^th decades.

Males are much more commonly affected than females (7:1 ratio).

Associations

• papillary renal cell carcinoma coexists in the same kidney in up to 50% (in small cases series ²)  

Clinical presentation

Most patients are asymptomatic and the tumor is discovered incidentally.

Pathology

Macroscopically, the tumors are well-circumscribed lesions comprising extensive tiny cysts with numerous thin septa, resulting in a spongy or "bubble wrap" appearance. Microscopically, the tumor is composed of tubular and cystic spaces separated by fibrous stroma.

Limited information from genetic studies suggest gene expression similar to papillary RCC ⁴.

Radiographic appearance

Ultrasound

• markedly hyperechoic (70%)
• posterior acoustic enhancement (50%), consistent with cystic nature
• no internal vascularity on color Doppler

CT 

• variable attenuation so may appear solid or cystic
• C+: contrast enhancement is usually mild or indeterminate given small amount of solid tissue

MRI

• T2: hyperintense due to cystic component, with septa
• T1 C+ (Gd): mild enhancement in small solid components or wall

Treatment and prognosis

Surgical resection is curative.

Recurrence and/or metastasis occur in less than 10% of cases.

Differential diagnosis

• cystic renal tumors
  • cystic nephroma
  • mixed epithelial and stromal tumor
  • multilocular cystic renal neoplasm of low malignant potential
• hyperechoic renal tumors
  • angiomyolipoma
  • renal cell carcinoma

See also

• WHO classification of tumors of the kidney