Signet‐ring cell adenocarcinoma of rectum: a histological, histochemical and electron microscopic study

A signet‐ring cell adenocarcinoma of rectum removed from a 71‐year‐old woman was examined by light and electron microscopy. Most of the mucin in the signet‐ring cells was of the neutral type, although acidic, mostly non‐sulphated, mucin was also present. Three other types of neoplastic cells were seen: undifferentiated, cells with intracytoplasmic lumina and argentaffin cells. The similarities between this tumour and tumours described in the stomach, appendix and breast are discussed.