Breast cancer incidence and familiality in Iceland during 75 years from 1921 to 1995.

Information in the Icelandic Cancer Registry on breast cancer and its collection of breast cancer families has been used to elucidate changes in breast cancer incidence by time period and by age, and the effect of degree of relationship and age on the familial risk of breast cancer. Since 1921 the incidence rates have increased, but the increase is significantly greater (2.06% per year) for ages over 44 years than for ages 20-44 (1.20% per year). It has been shown before that when familial risk is computed, the age of the proband influences the risk for the relatives. However, this study shows that the age of the relative is also important and with increasing age the familial risk decreases.