Study: Pausing hormone therapy to pursue pregnancy does not increase the short-term risk of early-stage cancer recurrence

Relevance: Medium-High

Strength of Science: Medium-High

Research Timeline: Post Approval

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Why is this research important?

Breast cancer is the most common cancer for women under age 40. Family planning and fertility is often a priority at these ages, and these concerns can affect quality of life and whether patients stay on treatment. Experts typically recommend 5-10 years of hormone therapy after surgery and chemotherapy for HR-positive breast cancer. To become pregnant, hormone therapy must be discontinued or interrupted. Because fertility decreases with age, delaying conception for 5-10 years to complete hormone therapy may greatly decrease the ability to have children.

Although past research shows that pregnancy after breast cancer does not worsen outcomes, more research is needed to show that it is safe to temporarily stop treatment to become pregnant.

What is the POSITIVE trial?
The POSITIVE trial was an international study designed to learn whether it is safe to interrupt hormone treatment for breast cancer to become pregnant after a recent diagnosis of HR-positive breast cancer. Birth rates and potential pregnancy complications were also studied.

POSITIVE followed 497 participants under age 42 who interrupted their hormone therapy to try to conceive. Most  participants:

• identified most frequently as white.
• were 35-39 years old.
• had stage 1 or 2 cancer.
• had received chemotherapy in addition to their hormone therapy.

Of the 497 participants, 59 had a known inherited mutation (38 in BRCA1 or BRCA2; the remainder in other genes).

Study findings

• 368 of 497 participants (68%) had at least one pregnancy.
  • Most of the women with successful pregnancies were younger.
  • Almost half of the women in the study who became pregnant used some sort of fertility treatment.
  • Pregnancy complications and birth defects occurred at rates similar to healthy women of the same age.
     
• Overall, women who interrupted their breast cancer hormone therapy for pregnancy:
  • had no increased risk of breast cancer during the 3 years of follow-up care.
  • 9% of women in the group that interrupted treatment were diagnosed with recurring breast cancer. This number was similar to women who did not stop hormone therapy (a different study provided the statistics for the risk of recurrence in women who did not stop hormone therapy).
• Most women with an inherited mutation did not have a cancer recurrence during this study.
  • 9 of 59 participants (15%) with an inherited mutation had a recurrence.
  • 35 of 457 participants (8%) without a known inherited mutation had a cancer recurrence.
    • Because the number of people with mutations and the number of cancer recurrences were small, it is unclear whether women with an inherited mutation had a similar or increased possibility of cancer returning. Additional research is needed to clarify this.

This study followed patients for only three years. Longer follow-up is needed to understand whether these results are similar when more time has passed since the initial diagnosis.