Cutaneous signet ring cell carcinoma: a report of a case and review of the literature.

Primary cutaneous signet-ring cell carcinoma (CSRCC) is a very unusual but distinctive clinicopathologic entity. It is defined as a diffuse malignant epithelial neoplasia localized in dermis and subcutis without epidermal involvement, showing variable amounts of signet ring cells, without evidence of a visceral adenocarcinoma. We report a case of CSRCC in a 70-year-old man along with its histologic and ultrastructural characteristics, and review of previous cases. We describe their main diagnostic features and discuss its wide differential diagnosis.