CK7 expression in primary cutaneous squamous cell carcinoma

Aim: To evaluate cytokeratin 7 (CK7) immunoreactivity in invasive primary cutaneous squamous cell carcinomas (SCCs). Methods: Twenty-seven primary cutaneous SCCs from 25 patients were evaluated for tumor grade using hematoxylin and eosin-stained slides and for percentage and intensity of immunoreactivity for CK7. All cases exhibited features of SCC with an in situ component. No glandular or tubular differentiation was present. Staining intensity was graded on a scale of 0-3, with 0 indicating no reaction. Of immunoreactive cases, percentage of tumor staining and distribution of immunoreactivity was documented. Results: Six of 27 SCCs (22%) exhibited immunostaining for CK7. Of those cases, three were poorly differentiated, exhibiting 2 to 3+ intensity in 5-15% of cells. Two were poorly differentiated, with 2 to 3+ intensity in 30-60% of cells. The remaining immunoreactive tumor was moderately differentiated, with 1+ intensity and 5% staining in an area of microinvasion. Conclusion: A subset of cutaneous SCCs, in particular, poorly differentiated tumors, may show focal-to-partial immunoreactivity for CK7. This is important to bear in mind when immunohistochemistry is used to distinguish SCC from simulants, such as porocarcinoma, or other adnexal carcinomas with squamous metaplasia.