Nick Mulcahy

June 03, 2017

CHICAGO – It's a finding that has been called "comforting," "reassuring," and "good news," here at the American Society of Clinical Oncology (ASCO) 2017 Annual Meeting.

The warm words are for the long-term results of a study of women who became pregnant after an early stage breast cancer diagnosis.

Lead study author Matteo Lambertini, MD, a medical oncologist at the Institut Jules Bordet in Brussels, Belgium, reported that, after a median follow-up of about 12 years from cancer diagnosis among 1200 women, there was no difference in disease-free survival between women who became pregnant and those who did not (hazard ratio [HR], 0.85; P = .15).

In other words, a pregnancy did not raise the risk of breast cancer recurrence or death.

Importantly, the finding also applied to women with estrogen-receptor (ER)-positive disease (HR, 0.94; P = .68), the primary study outcome.

Pregnancy after breast cancer is "safe" and "should not be discouraged," summarized Dr Lambertini during a press conference.

"It's wonderful to have these data," said Claudine Isaacs, MD, a medical oncologist at Georgetown Lombardi Comprehensive Cancer Center in Washington DC, who was not involved with the research. The new study is distinguished from similar past research by its large size, long-term follow-up, and detail of patients' receptor status, she pointed out.

Dr Lambertini explained that receptor status is important because ER-positive breast cancer is fueled by estrogen. There has been a fear that raised hormone levels associated with pregnancy might trigger the growth of residual cancer cells that may linger in the body after treatment.

Richard Schilsky, MD, chief medical officer of ASCO, who moderated the press conference, clarified that the conclusion about "safety" only referred to disease recurrence and not to complications of pregnancy, such as malformations.

However, the study is not the final word on managing patients with early stage breast cancer who want to get pregnant after treatment, said another expert.

"This study does not provide data on the optimal timing of a pregnancy following breast cancer treatment," observed Laura Spring, MD, a breast medical oncologist at Massachusetts General Hospital Cancer Center in Boston.

Dr Spring's comments refer to the current uncertainty about how to manage women who desire to be pregnant but also need endocrine therapy for 5 to 10 years to reduce the recurrence risk of ER-positive disease.

Insights will be potentially forthcoming from the prospective Pregnancy Outcome and Safety of Interrupting Therapy for Women with Endocrine Responsive Breast Cancer (POSITIVE) clinical trial, she told Medscape Medical News. The aim of the study is to investigate if temporary interruption of adjuvant endocrine therapy, with the goal to permit pregnancy, is associated with a higher risk of breast cancer recurrence.

Current Study Details

The new findings are an update of a multicenter European study with a retrospective, case-control design.

Dr Lambertini explained that patients with pregnancy after breast cancer (pregnant cohort) were matched (1:3) according to tumor and treatment characteristics with patients without subsequent pregnancy (nonpregnant cohort).

A total of 57% of patients had ER-positive breast cancer.

To adjust for guaranteed time bias, each nonpregnant patient was required to have been disease free for a minimum time not inferior to the time elapsing between breast cancer diagnosis and conception in the matched-pregnant cohort.

In secondary analyses, the investigators showed that there was no difference in disease-free survival between the cohorts, irrespective of whether women completed the pregnancy or had an abortion, became pregnant less than 2 years or greater than 2 years from breast cancer diagnosis, or had breastfed.

Investigators also found that, for the secondary outcome of overall survival, there was no difference between cohorts in patients with ER-positive breast cancer (HR, 0.84; P = .32). However, there was significantly improved overall survival in ER-negative patients in the pregnant cohort (HR, 0.58; P = .01), yielding a 42% lower risk of death.

Despite the unusual nature of this latter finding, Dr Lambertini did not call attention to it during the press conference. However, in a statement, he said: "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."

2017 annual meeting of the American Society of Clinical Oncology (ASCO). Abstract LBA10066 was presented June 3, 2017.

The study was in part supported by grants from Les Amis de l'Institut Bordet and the European School of Oncology. Two study authors report industry associations, as listed in the abstract. Dr Schilsky also reports industry associations. Dr Spring reports no disclosures.

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