New research confirms for the first time that it is safe for breast cancer patients diagnosed with estrogen receptor-positive breast cancer to become pregnant, despite previous concerns by doctors that pregnancy could lead to tumor recurrence by increasing estrogen levels in the body. In fact, the findings, presented at the 8th European Breast Cancer Conference in Vienna, suggest that pregnancy at any time in patients diagnosed with breast cancer does not increase the risk of cancer recurrence, even in the first two years after breast cancer. Moreover, these pregnant patients appear to survive longer compared to those who are not pregnant. Breast cancer is the most common tumor in women of childbearing age. As women start families later and survival improves for breast cancer patients, more and more breast cancer survivors want to have a child after their oncology treatment ends. In previous research, Dr. Hatem A. Azim, Jr. had suggested that despite concerns that pregnancy-induced changes in hormone levels might promote tumor recurrence or make it more aggressive, it appeared to be safe for women who were pregnant. However, the study did not confirm whether the study was only appropriate for estrogen receptor-positive female patients, and it is possible that this subgroup is most likely to be affected by pregnancy-induced hormone increases. In addition, the role of treatment in abortion in these patients, the timing of pregnancy, and the safety of breastfeeding remain unanswered questions. Therefore, Dr. Azim, a medical oncologist at the JulesBordet Institute (Brussels, Belgium), and colleagues conducted a study in several cities of 333 women with breast cancer who became pregnant at any time, and 874 women with breast cancer who did not become pregnant. Most importantly, however, the study included only women with estrogen receptor status (positive or negative) and known disease regression. In addition, there were no tumor recurrences in the control group while the women in the experimental group were pregnant, which allowed the researchers to adjust for a possible “healthy mom response” – a condition that may be influenced by the fact that women who become pregnant may be healthier than the breast cancer patients in the control group. According to Dr. Azim, 57 percent of the women were estrogen-positive, but the study showed no difference in tumor-free survival rates for either estrogen-positive or negative patients compared to those who were not pregnant. In addition, we found that women who became pregnant within two years of breast cancer diagnosis appeared to have a higher tumor-free survival rate than those who were not pregnant, but there was no significant trend over time. Because the results may be confounded by selection bias, the results should be interpreted with caution, so that pregnancy within two years of breast cancer diagnosis may be considered safe, but it should not be assumed that pregnancy is protective against tumor recurrence. The second aim of the study was to determine the effect of pregnancy on overall survival. We found that pregnancy in breast cancer patients reduced the risk of death compared to controls, regardless of estrogen receptor positivity. Neither breastfeeding nor miscarriage (either spontaneous or induced) affected the women’s outcomes. “It is common for some internists to advise women with breast cancer to abort because they fear that completing the pregnancy process is detrimental to their disease outcome. We have found this perception to be incorrect; the disease outcome is similar whether the gestational process is completed or not, and this is also true for estrogen receptor positivity. Therefore, for these patients, we do not advocate abortion for therapeutic reasons. Since only 30% of the patients were breastfeeding, we did the same analysis for breastfeeding, although this situation does not allow us to be more definitive about this indicator,” said Dr. Azim. He concluded: The study is the first to investigate the safety of pregnancy in estrogen receptor-positive breast cancer patients, corrected for the “healthy mother response”. Its findings give confidence that pregnancy is safe at any time after breast cancer diagnosis, regardless of estrogen receptor positivity. The study provides strong evidence to help doctors give appropriate answers to women completing breast cancer treatment who are asking about pregnancy.