Postmenopausal women with hormone receptor positive breast cancer may be offered adjuvant therapy with either tamoxifen or with an aromatase inhibitor. Aromatase inhibitors belong to a class of drugs that work by reducing the levels of estrogen in the body. Even if you have stopped menstruating, your body may still produce small amounts of estrogen in the adrenal glands, fat tissue and even breast tissue. These drugs first became available in the mid-to-late 1990s and have been shown to reduce the risk of breast cancer recurrence in postmenopausal women with early stage breast cancer. Such drugs include anastrozole (Arimidex®), exemestane (Aromasin®) and letrozole (Femara®).
Postmenopausal women with hormone-positive tumors may do just as well or perhaps a bit better with an aromatase inhibitor when compared to tamoxifen. It is not recommended for these women to undergo ovarian suppression as adjuvant treatment since their ovaries are not producing estrogen. Oophorectomy would be considered in this case in women who are BRCA 1 or 2 mutation carriers or have a strong family history of ovarian cancer as a preventive measure.
Patients who are diagnosed with early stage non-invasive breast cancer (DCIS) may be given tamoxifen to prevent breast cancer from occurring in the unaffected breast. The use of aromatase inhibitors in post menopausal women with DCIS is under investigation.
NOTE: Many women stop menstruating after receiving chemotherapy, often for several months or even a few years. This does not necessarily mean they are postmenopausal. It is possible that these women could still have functioning ovaries and premenopausal hormonal levels despite the absence of their menstrual periods. Also, ovarian function could still return unexpectedly. That said, women who are premenopausal, regardless of whether they experience temporary menopause because of treatments, should not be prescribed aromatase inhibitors (unless they are participating in specific clinical research studies). Aromatase inhibitors are typically reserved for postmenopausal women with breast cancer.
Side effects of aromatase inhibitors
Side effects of aromatase inhibitors are generally mild and well-tolerated. They include:
- Hot flashes
- Decreased interest in sexual activity
- Mood swings
- Hair thinning
- High cholesterol – You may need routine screenings. If cholesterol becomes a problem, you may be asked to reduce your intake of fat from meats and other animal products.
- Joint stiffness and pain, including carpal tunnel symptoms – In a small number of patients, this can be quite severe. If you develop severe symptoms your doctor may recommend that you temporarily stop taking it and then try another kind of aromatase inhibitor or tamoxifen.
Bone loss can be a complication of aromatase inhibitors. All women who have started or will start an aromatase inhibitor should talk to their primary care provider about having a bone density study (DEXA scan). Patients also should take at least the minimum recommended daily allowances of calcium and vitamin D. In patients with some evidence of bone loss, your doctor may recommend that you increase your exercise level or take a calcium supplement. If you are still experiencing problems with bone loss, your doctor may prescribe bone building drugs like a class of medications called bisphosphonates. The drug Evista® (raloxifene) is quite similar to tamoxifen and in general should be avoided in women previously diagnosed with breast cancer.
Interactions with menopausal hormonal treatment (hormone replacement therapy)
You should not routinely take any form of menopausal hormonal treatment (MHT) following a diagnosis of early stage breast cancer. If you are on a MHT at the time of diagnosis, speak to your doctor about how to go off this gradually. For example, your doctor may have concerns about the use of topical vaginal lubricants that contain estrogen due to the risk of estrogen being absorbed into the body.
Fortunately, some menopausal side effects (like vaginal dryness) can be reduced through symptom management.