1. Types of lower GI bleeding http://emedicine.medscape.com/article/188478-overview#ClinicalCauses

2. Neoplasm – bleeding can be from a polyp or carcinoma – Colon cancer is the predominant cause of neoplastic bleeding and is responsible for around 10% of rectal bleeding in patients older than 50 years – bleeding is usually low-grade, and is generally painless and intermittent – bleeding from these causes is usually occult – occurring as a result of mucosal ulceration or erosion from the surface of the tumor – though neoplastic bleeding can present as bright red blood per rectum, it is unusual for it to cause massive colonic bleeding. http://emedicine.medscape.com/article/188478-overview#ClinicalCauses http://bestpractice.bmj.com/best-practice/monograph/457/overview/aetiology.html

3. Mucosal ulceration/erosion from the surface of the tumor GI Bleeding