Sessile serrated polyposis cancer syndrome (SSPCS) is a rare disorder characterized by the presence of multiple serrated polyps in the colon and an increased personal and familial risk of colorectal cancer. SSPCS is defined by the World Health Organization (WHO) as the presence of at least 5 sessile serrated polyps (also known as 'sessile serrated adenomas,' or SSAs) proximal to the sigmoid colon, with 2 or more that are greater than 10 mm in diameter; or any number of serrated polyps in a person with a first-degree relative with SSPCS; or more than 20 serrated polyps of any size, distributed throughout the colon. SSAs are found in 2% of average-risk individuals undergoing their first screening colonoscopy, and are estimated to be responsible for 20 to 35% of all colon cancers. SSAs exhibit somatic mutations in the BRAF gene (164757), or less commonly in the KRAS gene (190070), early in their development. Individuals with SSPCS have a lifetime risk of colon cancer as high as 54% and may have a strong personal or family history of extracolonic cancers; first-degree relatives have a 32% risk of developing multiple serrated polyps and a 5-fold increased risk of colon cancer. An increased risk of pancreatic cancer has also been observed (summary by Gala et al., 2014).