Aromatase Inhibitors in Breast Cancer Treatment

Aromatase inhibitors are a central part of treatment for post-menopausal women with ER-positive breast cancers. I've written about the use and value of tamoxifen, which is a similar drug used primarily for younger women. Aromatase inhibitors, commonly referred to as AIs, serve the same purpose in limiting or blocking estrogen and making it unavailable to cancer cells, which rely on estrogen to help them grow.

Aromatase inhibitors are extremely potent and important treatments for ER-positive breast cancer. Just as most chemotherapy regimens reduce the risk of recurrence by 50%, so do these pills.

How do AIs work?

Aromatase inhibitors block the enzyme aromatase. Aromatase ordinarily turns the hormone androgen into small amounts of estrogen in the body. The AIs are not as effective in menstruating women as they can't manage to change the larger amount of estrogen that is present in their bodies. For post-menopausal women, however, they are more effective than tamoxifen. Sometimes younger women are offered the option of suppressing their ovarian function (either by drugs or surgery) and taking an AI instead of tamoxifen.

There are three different aromatase inhibitors available, all doing the same thing and all equally effective: Armidex (anastrozole), Aromasin (exemestane), and Femara (letrozole). Different medical oncologists have personal preferences of one over another, and there may be specific reasons to prescribe one for a particular patient. All three are taken as a daily pill. They may vary in cost, depending on someone's medical insurance. I have also known women who had reactions to one and not to another.

Aromatase inhibitors are extremely potent and important treatments for ER-positive breast cancer. Just as most chemotherapy regimens reduce the risk of recurrence by 50%, so do these pills. Here is the math: If, after diagnosis and staging, a woman is thought to have a 40% chance of recurrence without any systemic treatment, she might well have both chemo and then one of these endocrine therapies. The chemo would halve that 40% risk to a 20% risk of recurrence. The AI would then reduce that remaining 20% by half, bringing down her risk to 10%. Nothing brings the risk to 0%, but these clearly are much more encouraging numbers than the first quoted one.

What are the benefits and for how long do most patients take AIs?

There have been many studies comparing AIs with tamoxifen to determine which was more valuable in treating ER-positive breast cancer in post-menopausal women. Based on all of this research, most oncologists begin with an AI after the initial treatment of surgery, maybe radiation therapy, and maybe chemotherapy.

Some patients take the AI for five years. Those who are peri-menopausal at the time of diagnosis may begin with tamoxifen for 2 to 3 years and then make the switch to an AI. Sometimes patients are switched to an AI after 5 years of tamoxifen. There are many different recommendations about the total length of time that a patient continues with these drugs. Some stop after 5 years, others continue for 10, and some stay on the drug even longer. These are also based on individual patient-doctor conversations to make the right determination about what is best for a particular circumstance.

What is the psychological impact of taking an AI?

None of the studies, or at least none that I know of, have considered the psychological impact of taking an aromatase inhibitor. For most of us, it is quite reassuring to have these drugs once chemo has been completed. No one enjoys chemotherapy, but it is reassuring to know that the cancer is being actively treated.

Finishing chemo can be anxiety-raising for everyone, but it is even harder for most women with ER-negative breast cancers as they can't continue with the endocrine/hormonal treatments. I have known many women who wanted very much to continue on an AI after their oncologist felt that it was reasonable to stop. Again, there is no absolute answer about this one. Evidence-based medicine, upon which all good practice is based, does not confirm the wisdom of continuing indefinitely with an AI. For some women and situations, however, this may be the right course.

What are the possible side effects of the AIs?

Unlike the potentially serious side effects of tamoxifen, including blood clots, strokes, and endometrial cancer, the AIs are easier. They can cause some cardiac issues and, the more common worry, more bone loss (osteopenia and osteoporosis). Most women who take an AI have a bone density exam every year or two to monitor their bone strength. Medications, regular weight-bearing exercise, and adequate calcium and Vitamin D can help with bone loss.

There are other possible side effects that are less worrisome for our doctors but that can be problems for us. They include hair thinning (not total hair loss like chemo, but ongoing gradual thinning), weight gain, joint achiness, and diminished libido. Since these are things that happen commonly after a natural menopause, they are sometimes dismissed by doctors.

Some women may have troubles, e.g., headaches or hot flashes or generalized sense of malaise, with one of the aromatase inhibitors that vanish when they switch to another. Since these drugs are so important in our treatment, do consider trying one of the others if you are have having difficulty tolerating the first one. For most women, the biggest problem with AIs is remembering to take it each day.