Clear cell renal cell carcinoma
Clear cell renal cell carcinoma is the most common type of renal cell carcinoma.
The average age of onset of sporadic clear cell renal carcinoma is 61 years-old. In cases associated with Von Hippel-Lindau disease the average age of onset is 37 years .
Patients with the clear cell subtype of renal cell carcinoma are more likely to present with symptomatic disease and metastatic disease than with other types of renal cell carcinoma .
Clear cell renal cell carcinoma represents around 75-80% of cases of renal cell carcinoma and arises from the epithelium of the proximal tubule . Clear cell carcinoma is sporadic in over 95% of cases, in the 5% of familial cases most are seen in Von Hippel-Lindau disease . Common to both sporadic and familial forms is the loss of sequences on the short arm of chromosome 3 in 98% of tumors, usually by deletion or unbalanced translocation resulting in loss of 3p12 to 3p26. The second allele often shows somatic mutation or epigenetic inactivation through hypermethylation. Interestingly, this region contains the sequence for the Von Hippel-Lindau (VHL) gene, which is a tumor suppressor gene that normally results in increased expression of proteins of the ubiquitin ligase complex . The ubiquitin ligase complex normally identifies and tags proteins for destruction. Of particular relevance to clear cell carcinoma is ubiquitin mediated degradation of hypoxia inducible factor 1 (HIF-1), which is a pro-angiogenic factor normally expressed in hypoxic environments. As such, the loss of VHL allele results in increased levels of HIF-1 and resulting increase in pro-angiogenic factors such as VEGF, PDGF, TGF-α and TGF-β, leading to cellular dysplasia and ultimately neoplasia.
Tumors have a yellowish, golden appearance on sectioning due to the high lipid content .
Microscopically the tumor is characterized by :
- large cells with a uniform appearance
- abundant clear cytoplasm rich in glycogen and lipid
- high vascularity
Clear cell carcinoma compared to other forms of renal cell carcinoma is said to have :
- an exophytic appearance
- a greater degree of enhancement on the corticomedullary and nephrographic phases on multiphasic CT (compared to papillary cell carcinoma)
- a more heterogeneous appearance (due to multiple areas of internal necrosis, cystic change or hemorrhage)
MRI offers similar accuracy to CT in the detection of clear cell renal cell carcinoma .
- T1: heterogeneous appearance (due to multiple areas of internal necrosis, cystic change or hemorrhage)
- T2: hyperintense
- IP/OP: frequently containing microscopic fat resulting in focal or diffuse non-curvilinear signal loss in opposed phase (in 60% ) - this must not be mistaken for macroscopic fat frequently found in angiomyolipomas
Treatment and prognosis
Clear cell renal carcinoma has the worst prognosis of all renal cell carcinomas.