Cytokeratin expression in squamous cell carcinoma arising from hidradenitis suppurativa (acne inversa)

We have studied cytokeratin (CK) expression in two cases of well-differentiated and poorly differentiated squamous cell carcinoma (SCC) arising from hidradenitis suppurativa (HS) (acne inversa). In both cases, type A (infundibular-like keratinized) epithelia were observed. In type A epithelia, CK 1 and 10 expressions were decreased, and CK 14 and 17 were detectable in the whole layers. CK 7, 8, 15, 16 and 18 were not detected in type A epithelia. In tumor nests of well-differentiated SCC, CK 1 and 10 expressions were downregulated, and CK 14 expression was upregulated. In tumor nests of poorly differentiated SCC, CK 1 and 10 were not expressed, but simple epithelial keratins (CK 8, 18 and 19) were expressed. These changes of CK expression are related to malignant transformation from the sinus tract (type A epithelium) in HS to SCC.