[Clear cells in cutaneous squamous cell carcinoma]

Although few cases of squamous cell carcinoma (SCC) with clear cells have been published, we believe that these cells are often present in SCC.

We studied 249 SCCs, analyzing a number of clinical and histological variables. Various immunohistochemical techniques (immunoperoxidase method) were used to determine whether adnexal differentiation was present.

There were 96 SCCs with a proportion of clear cells of over 25 %. Advanced or established SCCs and SCCs associated with Bowen disease contained a larger proportion of clear cells. We defined 2 histological patterns: a) clear cells around the keratin pearls of SCCs arising from pre-existing actinic keratosis and with indirect signs of human papilloma virus infection in hair follicles; and b) clear cells that simulate adnexal differentiation in lesions arising on pre-existing Bowen disease lesions. There were also 19 carcinomas with true adnexal differentiation.

Clear cells are frequently observed in SCC, though large numbers of clear cells are present only in certain SCCs. The appearance of clear cells in SCCs is progressive and they are only present in more advanced SCC. The presence of clear cells is suggestive of adnexal differentiation; however, in the majority of cases, their presence is due to infiltration of normal adnexal structures by the cells of pagetoid Bowen disease. True adnexal differentiation exists only in a small percentage of cases (7.6 % in our study). The histological pattern described as clear cells around keratin pearls practically rules out this differentiation.