CHICAGO — A study gives reassuring news for breast cancer survivors who want to have children. Those who later became pregnant were no more likely to have their cancer come back than those who did not have a baby.

It’s a big issue – the average age of moms has been rising in the United States, and more women are being diagnosed with breast cancer in their childbearing years. About 11 percent of new breast cancer cases in the U.S. are in women under 45.

The study, done in Europe, is the largest so far on women whose cancers were fueled by hormones, which rise in pregnancy and theoretically, might spur a recurrence.

“Having a family is one of the most important achievements in a person’s life,” said study leader Dr. Matteo Lambertini of the Jules Bordet Institute in Brussels, Belgium. These results show that “pregnancy after breast cancer can be considered safe.”

The research involved more than 1,200 breast cancer survivors. More than half had tumors whose growth was fueled by estrogen. After treatment, 333 became pregnant, about two and a half years after their cancer diagnosis, on average. Researchers compared them to 874 other survivors, matched for tumor type and other things, who did not.

More than 12 years after conception, recurrence rates were similar in both groups. Abortion had no impact on the rates either.

There was information on breast-feeding for only 64 of the moms, but 25 reported doing so successfully, suggesting it’s possible for some women even after breast surgery.

The results show “fairly convincingly” that women don’t have to worry, said Dr. Richard Schilsky, chief medical officer for the American Society of Clinical Oncology. The group featured the study at its annual conference that ended Tuesday in Chicago.