A primary or metastatic malignant neoplasm that affects the rectum. Representative examples include carcinoma, lymphoma, and sarcoma. The disease is rectal cancer (MONDO_0006519). Also known as: cancer of rectum, malignant neoplasm of rectum, malignant neoplasm of the rectum, malignant rectal neoplasm, malignant rectal tumor, malignant rectal tumour, malignant rectum neoplasm, malignant rectum tumor.