Signet-ring squamous cell carcinoma.

Among carcinomas, signet-ring morphologic characteristics have been regarded as pathognomonic of adenocarcinoma. This report presents the case of a poorly differentiated cutaneous squamous cell carcinoma with a monodispersed, invasive signet-ring component. Kreyberg stains had negative results for mucin. Immunohistochemical analysis demonstrated that concentric rings in the signet-ring cells were composed of keratin. To the best of the authors' knowledge, this is the first report of signet-ring squamous cell carcinoma. Another feature that bears emphasis is that this squamous cell carcinoma led to the death of the patient, even though it originated in a field of actinic keratosis.