Risk factors for gastric cancer include: Having a mutation in a family gene related to gastric cancer. Having 1 family member <40 years of age diagnosed with gastric cancer. 2 family members diagnosed with gastric cancer in a first- or second-degree relative, 1 of whom is <50 years of age 3 family members (regardless of age) diagnosed with gastric cancer in first or second degree relatives. 1 family member <50 years old was diagnosed with both gastric cancer and breast cancer. 1 family member diagnosed with gastric cancer and 1 of the first- or second-degree relatives diagnosed with breast cancer, 1 of whom was <50 years old.