rectum carcinoma in situ (MONDO_0004725) is a in situ carcinoma that involves the rectum. Also known as: carcinoma in situ of rectum, carcinoma in situ of the rectum, marked dysplasia of rectum, marked dysplasia of the rectum, marked rectal dysplasia, rectal carcinoma in situ, rectum in situ carcinoma, severe dysplasia of rectum.