(ChemotherapyAdvisor) – Pregnancy is safe and should not be discouraged following a diagnosis of breast cancer, regardless of estrogen receptor status, according to results of a multicenter case-control study reported during the 8th European Breast Cancer Conference in Vienna, Austria, March 21.

In addition, Hatem A. Azim, Jr., MD, Jules Bordet Institute, Brussels, Belgium, and colleagues found that pregnancy within two years after a diagnosis of breast cancer appeared to have a protective effect.

They enrolled 1,207 women; 333 who had become pregnant following a breast cancer diagnosis were matched with 874 similar patients with breast cancer who did not become pregnant. A total of 57% were estrogen receptor-positive (ER+) and 44% were node positive. Mean age was 34 years (range, 21 to 48 years). For patients with ER+ tumors, the one-year end point was disease-free survival, calculated from date of conception or, in the control group, date of diagnosis plus the time between diagnosis and conception of the matched case. In women with ER-negative (ER–) disease, disease-free survival was a two-year end point.

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The study included only women whose estrogen receptor status and disease outcome were known. In addition, women in the control group had not relapsed at the time the matched case became pregnant, which enabled the researchers to adjust as far as possible for the “healthy mother effect,” a phenomenon whereby the results could be influenced by the fact the women who became pregnant might be healthier than those in the control group.

At a median follow-up of 4.7 years from conception, 30% of women had disease recurrence. Comparing the pregnant and control groups, no differences were observed in disease-free survival for either the ER+ (HR=0.91) or ER– (HR=0.76) cohorts. In a predefined subgroup analysis, patients who became pregnant within two years following a diagnosis of breast cancer had better disease-free survival vs. matched controls (HR=0.64; P=0.008); HR=0.72 in ER+ and 0.58 in ER– patients.

Neither breastfeeding nor abortion had an effect on breast cancer outcome. “Frequently, when women with a history of breast cancer become pregnant, some physicians advise them to have an abortion for fear that completing the pregnancy could have a detrimental effect on the outcome of their disease,” said Dr. Azim. “We found that this was not true and the outcome was similar, irrespective of whether the pregnancy was completed or not. This was also the case both for women with ER+ and ER– disease. Hence, abortion should not be promoted for therapeutic reasons in these patients. The same analysis was done for breastfeeding, although we knew about breastfeeding in only 30% of the patients, which hinders providing a firm conclusion in this regard,” he added.

Results of this study provide strong evidence to help counsel women seeking to become pregnant following completion of breast cancer therapy. The study did not address optimal duration of adjuvant hormonal therapy.

Abstract (To view abstract, please click on link and put “Azim” in the author search box.)