Introduction:

In some cases, it is difficult to evaluate histological invasion in squamous cell carcinomas (SCCs) and to discriminate them from in situ squamous cell carcinomas (ISSCCs). Cytokeratin (CK) 17 is induced by activated keratinocytes, and its expression is associated with disease progression in SCCs of certain organs. In this study, the utility of CK17 as an adjunct immunohistochemical marker to facilitate the diagnosis of invasion in cutaneous SCCs was investigated.

Methods:

Immunohistochemical staining for CK17 was evaluated in 19 ISSCCs and 27 invasive SCCs (IVSCCs). Staining patterns were defined as diffuse (DF), patchy (PT), suprabasal/central (SC), or peripheral/ basal (PB). SCCs showing only a DF pattern were interpreted as testing positive for CK17 immunoexpression. SCCs were interpreted to as testing negative if there was no CK17 expression or they showed other staining patterns.

Results:

All ISSCCs tested negative for CK17 immunoexpression. While no staining was detected in 7 of the 19 ISSCCs, the PT pattern was observed in 6 and the SC pattern in 6. Twenty-two (81%) IVSCCs tested positive. Of the 5 IVSCCs that tested negative, 4 showed the PB pattern and 1 showed the SC pattern. The sensitivity and specificity of CK17 immunohistochemical staining for identifying invasion were 81% and 100%, respectively.

Conclusion:

CK17 may be a useful immunohistochemical marker for identifying invasion in cutaneous SCCs and may help pathologists determine surgical margins.

Keywords: Cytokeratin 17, in situ squamous cell carcinoma, invasive squamous cell carcinoma, Bowen disease, skin, actinic keratosis