Familial Intestinal Gastric Cancer (FIGC) remains genetically unexplained and poorly characterized, preventing the design of testing criteria for genetic diagnosis. We analyzed family trees from FIGC families and compared their tumour and normal genetic profiles with those of sporadic stomach cancer patients. We found that FIGC families present 2 or more stomach cancers, but may also show colorectal and breast cancers; that stomach cancer arises, on average, 10 years earlier than in patients with sporadic stomach cancer, and; that tumours and normal cells from familial cases are genetically different sporadic cases. Our study proposes the first testing criteria for FIGC families and provides compelling evidence that this familial disease is genetically determined. (By Dr. Carla Oliveira, https://jmg.bmj.com/content/early/2020/02/17/jmedgenet-2019-106346 )