An invasive adenocarcinoma of the rectum characterized by the presence of pools of extracellular mucin. Malignant glandular epithelial cells are present in the mucin collections. Mucin constitutes more than 50% of the lesion. The disease is MONDO_0002748 (rectum mucinous adenocarcinoma). Also known as: colloid adenocarcinoma of rectum, colloid adenocarcinoma of the rectum, colloidal adenocarcinoma of rectum, colloidal adenocarcinoma of the rectum, mucinous adenocarcinoma of rectum, mucinous adenocarcinoma of the rectum, rectal colloid adenocarcinoma, rectal colloidal adenocarcinoma.