Delay pregnancy nine months after tamoxifen

The new advice is a good reminder to discuss fertility with breast cancer patients.

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Women are now advised to wait at least nine months, not two, to become pregnant after coming off the hormonal breast cancer treatment, tamoxifen.

The updated advice from the TGA reinforces the need for clinicians to have conversations with affected patients about fertility.

The recommendation to use contraception for at least nine months follows the US regulator’s guidance, updated in May 2019, which stipulates a period of at least six months plus five elimination half-lives after ceasing genotoxic pharmaceuticals.

While breast cancer is most often diagnosed in women over 50, younger women of childbearing age are affected too.

In 2020, it accounted for 23% of cancer diagnoses and 21% of cancer deaths in women aged 20-39. This makes it the most diagnosed form of cancer and cancer death in that cohort.

Last week, the Australian regulator reiterated that the drug was contraindicated in pregnancy and that clinicians should ensure patients weren’t pregnant before starting the treatment.

It said this was because tamoxifen was a Category B3 medicine and “a small number of reports of spontaneous abortions, birth defects and fetal deaths have occurred after women have taken tamoxifen, although no causal relationship has been established.”

“Women of child-bearing potential should be advised to use barrier or other non-hormonal contraceptive methods if they are sexually active, both during treatment and for nine months after treatment has ended.”

Moreover, they should be informed about potential risks to the fetus if they became pregnant while taking drug or in the nine month window afterwards, the TGA announcement said.

But research published this year in the oncology journal Cancers suggests that the topic of contraception is not sufficiently addressed with young breast cancer patients.

Medical oncologist Professor Bogda Koczwara, from Flinders University in Adelaide, said the latest advice reinforced the need to have conversations with younger patients about both contraception and fertility, to get the timing right. 

“When I see young women with the diagnosis of breast cancer, we actually have a conversation with them along the lines of ‘what are your plans for the family in the long run?’,” said Professor Koczwara.

“One aspect is you need to be off tamoxifen for an extended period of time,” she said. “You need to take into account your fertility potential, which is very much age-dependent, your duration of treatment and your optimal treatment.”

This required some careful planning, she added.

A review of pregnancy outcomes after breast cancer diagnosis showed that pregnancy rates after treatment were on average 40% lower than for the general population.

Nevertheless, hormone therapy did not appear to cause infertility, because women took the drug for around five to 10 years and their fertility naturally declined during this time. Professor Koczwara noted there was reassuring research suggesting women who had breast cancer did not have worse pregnancy outcomes than women without the cancer.

She also emphasised the benefits of discussing fertility and future plans for a family: “These days, we have good data about pregnancy risks. We have a very good system of fertility advice.”

“When they come in to talk about a new cancer diagnosis, the last thing on their mind often is pregnancy, but sometimes that is actually the first thing on their mind.”

Breast Cancer Network Australia CEO, Kirsten Pilatti, added that it was important not to jump to conclusions about a patient’s plans.

“We know from women who have been diagnosed that clinicians will readily assume because they have two kids that they don’t want any more, and so actually not have the conversations with them, or assume they’re too old.

“There are [also] a lot of assumptions made about single women that aren’t helpful,” she added.

Ms Pilatti said the speed at which these women had to make many tough decisions added to the challenge.

Importantly, there were fertility opportunities available at every stage, said Ms Pilatti. “So even if they go into having chemo and early menopause, and they think there’s nothing they can do, there are still different options for them.”