Morphological & immunohistochemical spectrum in anorectal malignancies

The morphological features of 62 anorectal malignancies diagnosed on sigmoidoscopic biopsy were studied. On haemotoxylin and eosin staining the tumours were diagnosed as adenocarcinomas (43), squamous cell carcinoma (12), malignant melanoma (3), carcinoid (2), clear cell carcinoma (1) and poorly differentiated carcinoma (1). PAS Alcian blue, Grimelius silver stain, AgNOR and immunohistochemical stain for carcinoembryonic antigen (CEA) and human papilloma virus (HPV) were done to further categorise these tumours. The ages of the patients varied from 18 to 77 yr (mean 43.7 yr) and the male: female ratio was 2:1. PAS Alcian blue staining was helpful in differentiating mucinous from non-mucinous adenocarcinomas and reclassifying one poorly differentiated carcinoma as mucin secreting adenocarcinoma. Also, it clearly identified pagetoid spread in two cases of adenocarcinomas. Grimelius silver stain was strongly positive in melanomas and neuroendocrine tumours. Basal silver staining was visualised in metaplastic foci but was absent in dysplastic epithelium. AgNOR counts may be considered useful in differentiating melanomas (high counts) from spindle cell variant of squamous carcinomas (low counts). High AgNOR counts and strong Grimelius positivity in clear cell carcinoma suggested its melanotic origin. Immunostaining for CEA and HPV were of limited value. CEA was positive in the majority of the adenocarcinomas while HPV could only be demonstrated in two squamous cell carcinomas.