Ask the expert: aromatase inhibitors and tamoxifen

Dr Belinda Yeo is a medical oncologist at Melbourne’s Olivia Newton-John Cancer Wellness Centre. She is also a Clinician Scientist at the Olivia Newton-John Cancer Research Institute. Her research focuses on estimating the risk of breast cancer recurrence in patients and the benefits of personalising treatment accordingly.

What is hormone blocking therapy and how does it work?

Hormone blocking, or endocrine, therapy is used for women who have hormone receptor positive breast cancer. For people with early breast cancer, the goal is to stop the cancer recurring. For people with metastatic breast
cancer, the goal is to stop the hormones stimulating the cancer cells. Tamoxifen is effective in pre- and post-menopausal women and works by blocking hormone receptors. Aromatase inhibitors such as anastrozole (Arimidex),
letrozole (Femara), and exemestane (Aromasin) only work for postmenopausal women (natural or treatment induced). They block the enzyme aromatase, which reduces the amount of oestrogen circulating in your body.

What side effects do these drugs have?

Common side effects are hot flushes, mood changes, dry skin, thinning hair and a loss of bone density.

Which drug is the best?

I think the “best” agent is whichever one you can tolerate. We do take into account your breast cancer pathology and whether or not you are menopausal, but since you will be on endocrine therapy for at least five years, it is important to make sure any side effects aren’t impacting your ability to function normally. As oncologists, we want to make sure you can stay on whatever therapy is recommended as consistently as possible.

Can I take a break from these therapies? Is there a downside?

I’m a big fan of a treatment holiday of a month or two months. Taking a break doesn’t mean you’re a failure – the side effects can be really hard to deal with. These drugs stay in your system for a while, so you won’t lose any of the effect the drug has had. Taking a break can provide relief from the side effects and also gives you an opportunity to figure out if the symptoms are due to the hormone blocking therapy or potentially another issue.

What can I do if my oncologist doesn’t take seriously the impact side effects are having on my life?

It’s important that you feel comfortable raising your concerns with your oncologist, as your relationship with them will be a long-term one. Book a longer appointment with your oncologist to make sure there’s enough time
to discuss any issues you have, like side effects. I’d also recommend bringing a support person to your appointment – maybe even your breast care nurse – who can help you to advocate for yourself. Your GP can also help
you with managing side effects. I’ve heard from many women who find acupuncture helps, and that exercising makes a difference for them. Of course, exercise will also help with less visible side effects such as loss of bone density.

More information:

For more information on the pros and cons of hormone therapy, you can find BCNA’s Hormone therapy resources at

You can also watch BCNA’s recent webcast Hormone blocking therapy: is it worth it? on our website. Go here to register.

Issue 85
Spring 2019