The rectum is the last six inches of the large intestine, also called the colon. 

The rectum and connects to the anal canal, which leads to the anus which opens to the outside of the body. Because the rectum and colon are both part of the large intestine, many conditions of either are often referred to as colorectal.

Most rectal tumors form inside the lining of the rectum. Tumors can be either benign (non-cancerous) or malignant (cancerous). 

Tumors that are malignant begin when cells grow in an abnormal fashion.

Types of benign rectal tumors include:

Neoplastic epithelial polyps (premalignant)
Adenomas, most common type – three varieties: tubular (usually found in rectosigmoid), villious (usually found in the rectum and sigmoid), and tubulovillous

Non-neoplastic epithelial polyps
Hyperplastic polyps
Hamartomas
Juvenile polyps (generally found in children under the age of 10)
Peutz-Jeghers’ polyps (result from rare disease called Peutz-Jegher’s syndrome)
Inflammatory polyps, usually occur in patients with inflammatory bowel disease
Lymphoid polyps

Types of malignant rectal tumors include:
Adenocarcinoma
Aggressive neuroendocrine tumor
Leiomyosarcoma
Lymphoma
Mucinous Adenocarcinoma
Signet Ring Cell Adenocarinoma