Women who get pregnant after being treated for breast cancer do not have a higher risk of cancer recurrence, even if they have estrogen-sensitive tumors, according to a study presented at the American Society of Clinical Oncology (ASCO) annual meeting last week in Chicago.
Long-term overall survival and disease-free survival without relapse were similar for women who became pregnant and those who did not conceive, showing that women with a history of breast cancer can safely have children.
“These data provide reassurance to breast cancer survivors that having a baby after a breast cancer diagnosis may not increase the chance of their cancer coming back,” Erica L. Mayer, MD, of the Dana Farber Cancer Institute in Boston, said in an ASCO press statement. “For many young women around the world who want to grow and expand their families, it’s very comforting news.”
Unlike many other types of cancer, breast cancer often strikes young women during their reproductive years. A common question among breast cancer survivors is whether getting pregnant could increase the risk of cancer relapse.
Breast cancer is classified according to what kind of receptors it expresses. A majority of breast tumors carry estrogen receptors (known as ER-positive) or progesterone receptors (PR-positive). Other tumors express another receptor called HER2 (human epidermal growth factor receptor 2), while triple-negative breast cancer doesn’t express any of these receptors.
Estrogen encourages the growth of ER-positive breast cancer, and it is typically treated with hormone-blocking therapy. Adjuvant or follow-up hormone therapy may be used after surgery to prevent proliferation of any remaining cancer cells, usually for at least five years. Women with this type of cancer and their doctors may be concerned about whether higher levels of estrogen during pregnancy will promote the growth of residual cancer and whether stopping hormone therapy could allow cancer to return after remission.
Matteo Lambertini, MD, of Institut Jules Bordet in Brussels, and colleagues conducted the largest study to date looking at the safety of pregnancy in women with a history of ER-positive breast cancer.
This retrospective study included 1,207 women under age 50 in Europe and the United States who had been diagnosed with early-stage non-metastatic breast cancer. The 333 women who became pregnant were matched with 874 women with similar tumor types and treatment experience who did not conceive. Fifty-seven percent had ER-positive breast cancer. Those who became pregnant did so a median of 2.4 years after cancer diagnosis. Those who became pregnant were slightly younger than those who did not (31 years versus 34 years).
The researchers previously reported that women with ER-positive breast cancer did not experience detrimental outcomes within the first five years after becoming pregnant. At ASCO they presented longer-term data showing that this was still the case after up to 12.5 years of follow-up.
After a median 10 years of follow-up after cancer diagnosis, disease-free survival was statistically similar for women who became pregnant and those who did not. This was true for the group as a whole, for women with ER-positive cancer and for those with ER-negative cancer. Only a small number of women were followed past 10 years, but among them, the disease-free survival rate appeared higher for women who became pregnant.
Overall survival did not differ between women with ER-positive cancer who became pregnant and those who did not. However, women with ER-negative cancer who got pregnant had a significant 42 percent lower likelihood of death than those who did not conceive.
“It’s possible that pregnancy could be a protective factor for patients with ER-negative breast cancer, through either immune system mechanisms or hormonal mechanisms, but we need more research into this,” Lambertini said in an ASCO press statement.
Women who became pregnant within two years after their cancer diagnosis were not at greater risk of cancer recurrence or death than those who waited longer. Women who had abortions were no more likely to experience cancer relapse, and breast feeding also had no apparent effect on cancer outcomes.
“Our findings confirm that pregnancy after breast cancer should not be discouraged, even for women with ER-positive cancer,” Lambertini said. “However, when deciding how long to wait before becoming pregnant, patients and doctors should consider each woman’s personal risk for recurrence, particularly for women who need adjuvant hormone therapy.”
An ongoing study called POSITIVE is looking at whether temporarily interrupting hormone therapy to allow pregnancy increases the risk of breast cancer recurrence. More research is also needed on the effect of pregnancy for women with BRCA mutations, who typically develop breast cancer at a younger age.