Maternal and fetal outcome after breast cancer in pregnancy.

We compared 118 women with breast cancer (119 pregnancies) with 269 nonpregnant control subjects matched on important prognostic factors. The distribution of breast cancer stages among the 118 pregnant women was compared with that among 5115 cases of breast cancer in women of reproductive age. Fetal outcome was compared with that of a control group matched for maternal age. Women having breast cancer in pregnancy were 2.5 times more likely to have metastatic disease (95% confidence interval 1.1 to 5.3) and had a significantly lower chance of having stage I disease (p = 0.015). Survival of pregnant women did not differ from that of the controls. Birth weights of babies born to women with breast cancer were significantly lower than those of control babies after gestational age was adjusted for (3010 +/- 787 vs 3451 +/- 515 gm, p = 0.016). The two stillbirths in 85 pregnancies that continued to term (2.4%) was not statistically different from the 1.1% rate for Ontario. We analyzed all 223 births occurring in women who had any form of cancer in the same hospital during the same 30 years. There were 10 stillbirths among these 223 cases (4.4%), significantly more than expected in Ontario (p less than 0.0005; relative risk of 4.23 with 95% confidence interval 2.0 to 7.8). Our data suggest that pregnant women are at a higher risk of presenting with advanced disease because pregnancy impedes early cancer detection.