Effect of pregnancy on prognosis for young women with breast cancer.

Breast cancer in women under 30 years old carries a poor prognosis, for reasons that have not been identified. This study aimed to identify prognostic factors in this age group. Special attention was paid to the history of pregnancy. The clinical presentation and course of breast cancer was documented for 407 women, aged 20-29 years, who registered between 1978 and 1988 at one of nine cancer centres. Eligible patients had histologically confirmed local or regional invasive breast carcinoma, and received part or all of their initial therapy at the participating hospital. For patients whose breast cancers were diagnosed during pregnancy, the risk of dying from breast cancer was significantly greater than that of women who had never been pregnant (relative risk 3.26 [95% CI 1.81-5.87], p = 0.0004). Adjustment for number of axillary nodes affected and tumour diameter reduced the relative risk only slightly (2.83 [1.24-6.45], p = 0.023). For each 1-year increment in the time between the latest previous pregnancy and breast cancer diagnosis, the risk of dying decreased by 15% (relative risk 0.85, p = 0.011). Thus concurrent or recent previous pregnancy adversely affects survival of breast cancer in young women. The size of the effect is such that it probably contributes substantially to the poor prognosis of breast cancer in this age group as a whole.