Sporadic clear cell renal cell carcinoma with diffuse cytokeratin 7 immunoreactivity

Aims: Clear cell renal cell carcinoma (CRCC) with diffuse immunoreactivity for CK7 is described. Methods: All cases of CRCC, measuring 20mm or less in diameter over a period of 10 years, were examined. Areas of regenerative epithelial cell nests (REC) were also examined. Results: Fifteen specimens containing 29 nodules were diagnosed as CRCC due to the characteristic clear cytoplasm. Of these 29 nodules, 21 showed diffuse CK7 positivity while eight showed CK7 negativity. The CK7 positive CRCC measured less than 16mm and contained varying proportions of tumour cells with chromophil cytoplasm. Architecturally, CK7 positive CRCC consisted of cysts and solid cell nests with tubulo-acinar formations or papillary formations. Immunostaining for AMACR, CD10 and RCC showed negative or focal reactivity in the CK7 positive CRCC, frequently positive reactivity in CK7 negative CRCC and negative reactivity in REC which also displayed strong CK7 reactivity. The ten patients with 21 CK7 positive CRCC developed no metastatic disease over a follow up time that ranged from 1 to 10 years (mean of 3 years). Conclusions: CRCC characterised by diffuse CK7 positivity represents a distinct type of CRCC with characteristic histopathological and immunohistochemical features.