Carcinoma arising in epidermoid cyst: a case series and aetiological investigation of human papillomavirus

Sir, Malignant degeneration within an epidermoid cyst (EC) is both enigmatic and rare. Previous case reports show a frequency of carcinoma arising in EC ranging between 0·033% and 11%.1,2 In all series, adults predominate with an equal gender frequency, and a varied anatomical distribution is reported.1,2 Little is known regarding the aetiology or histogenesis of this condition. We report the largest series to date and address the potential role of human papillomavirus (HPV). Cases of squamous cell carcinoma (SCC) arising in EC were retrieved from the pathology files of three centres. For immunohistochemistry a polyclonal anti‐HPV antibody (NCL‐PVp; Novocastra, Newcastle upon Tyne, U.K.) was used. Standard polymerase chain reaction (PCR) protocol was followed employing 21‐mer primer sets to the conserved E1 open reading frame, producing a genus‐specific 850‐bp segment.3 Five cases of SCC in EC were identified in three men and two women. Lesions were limited to the face, neck or trunk. The mean age of patients was 56·7 years (range 21–80). The mean follow‐up was 2·6 years without recurrence or metastasis. The five cases of SCC arising in EC represented a frequency of of 0·0085% of all SCC and 0·011% of all excised EC.