Family history of cancer among cancer patients.

Family history of cancer was examined for 9,131 cancer patients who were reported to the Aichi Cancer Registry in 1979-1981, and were over 20 years old at diagnosis. The rate of patients whose parents and/or siblings had cancer of any site was 24.5%. The rate was 9.2% for father, 8.4% for mother, 6.0% for brother(s), and 5.2% for sister(s). A significant site concordance between study patient and family member with cancer was observed for cancer of the breast, colon and rectum, and stomach. The rate of family history of breast cancer patients was 3.3 times higher than the corresponding rate for other cancer patients (3.1% vs 0.9%). Similarly, the ratio was 2.2 in colon and rectum cancer (4.2% vs 1.9%), and 1.6 in stomach cancer (16.5% vs 10.1%). An increased risk of cancer was observed when both brother and sister had cancer. This may suggest an important role of environmental exposure at an early age, as well as genetic factors, in the development of cancer. The age distribution curve of the colon and rectum cancer patients who had a family history of the same cancer was found to be bimodal with the larger peak in the 40s and the smaller peak in the 70s. This may suggest a differential contribution of genetic and environmental factors to the development of colon and rectum cancer.