Breast cancer, genetics, and age at first pregnancy.

Hereditary breast cancer shows a distinctive natural history characterised by an earlier age of onset, excess bilaterality, vertical transmission, heterogeneous tumour associations, and improved survival when compared to its sporadic counterpart. To date, very little attention has been given to interrelationships between breast cancer risk factors and genetics. In the general population, early age of first term pregnancy has been generally accepted as protective against breast cancer. In addition, recent findings suggest that an early age of first pregnancy may be associated with an earlier age of breast cancer diagnosis. We studied the age at first pregnancy and age at onset of breast cancer among 162 females at 50% genetic risk, 72 of whom had already developed the disease. We then compared them to 154 consecutively ascertained breast cancer patients from the Creighton Cancer Center. In the hereditary subset (1) early first term pregnancy did not alter the frequency of breast cancer; (2) early age at first term pregnancy was not associated with an earlier age at cancer diagnosis; and (3) age of breast cancer onset in nulliparous females was not significantly lower than that in females having at least one term pregnancy. We speculate, therefore, that in our hereditary population, pregnancy does not influence the natural history of breast cancer in the same way that it does in the population at large.