Women with early-stage breast cancer who are treated with radiation therapy and subsequently become pregnant do not appear to increase their risk that the cancer will recur, researchers reported here at the 52nd Annual Meeting of the American Society for Radiation Oncology (ASTRO).

"What we found in our study was that the risk of recurrence was lower among women who became pregnant," said Ahlam Aljizani, MD, Ottawa Regional Cancer Center, Ottawa, Ontario.

"There is controversy whether pregnancy affects risk of recurrence after treatment for early breast cancer," she noted. "Although several studies have suggested a neutral or even beneficial effect, there is ongoing concern regarding the potential negative impact of pregnancy due to stimulatory effects of oestrogen on tumour growth."

In her study of 201 women with early breast cancer, 28.2% of the 39 patients who later became pregnant had a recurrence compared with 55.6% of those who did not get pregnant (P =.002), Dr. Aljizani said in her poster discussion presentation on November 1.

She and her colleagues reviewed the medical records of women treated for early breast cancer between 1961 and 2005 at their institution. The average age of the women was about 28 years. The women were treated with either breast-conserving surgery followed by radiation or mastectomy. They were followed for an average of about 11 years, during which time about half of the patients had a recurrence.

Among women who became pregnant, the risk of recurrence was unaffected by the time of pregnancy, with those who conceived in the 12 months after diagnosis were no more likely to have their cancer come back than those who got pregnant in later years.

The choice of treatment only affected recurrence rates among women who did not get pregnant, Dr. Aljizani said. Among these women, those who got breast-conserving surgery and radiation were 54% less likely to have their cancer come back, compared with those who had a mastectomy.

The analysis took into account other factors that affect the risk of recurrence, including whether the cancer had spread to the lymph nodes and choice of treatment, she said.

There have been fears that the increased levels of hormones during pregnancy might stimulate tumour growth, said Phillip Devlin, MD, Harvard Medical School, Boston, Massachusetts, who commented on the study. "This study does not support those fears," he said. Dr. Devlin was not involved with the work.

The retrospective nature of the study also may limit its generalisation. Dr. Devlin suggested that it might have been that women who didn't get pregnant after breast cancer treatment were overall sicker than the women who did get pregnant and that, therefore, would impact results.