Exemestane (Aromasin), an aromatase inhibitor, was found to lower invasive breast cancer rates by 65% in moderate and high-risk postmenopausal females, researchers at the Massachusetts General Hospital Cancer Center in Boston reported. An aromatase inhibitor inhibits aromatase, an enzyme involved in the production of estrogen estradiol. Many breast cancers are promoted by estrogens.

After the menopause, most estrogen comes from the action of aromatase. Aromatase inhibitors can be very effective for treating estrogen dependent tumors, especially after the menopause.

Examples of currently FDA approved aromatase inhibitors include exemestane (Aromasin), anastrazole (Arimidex), and letrozole (Femara). Aromasin is now available in a generic version.

A double-blind MAP.3 trial involving 4,560 post-menopausal females found that Aromasin significantly reduced their risk of developing invasive breast cancers after 3 years, and without serious side effects.

Director of Breast Cancer Research at Massachusetts General Hospital, Dr. Paul Goss said that the researchers were “delighted” with the 65% reduction risk. He stressed, however, that the study only had a three-year median follow-up.

Dr. Goss presented the trial results at the American Society of Clinical Oncology Annual Meeting in Chicago.

1.3 million breast cancer diagnoses are made each year worldwide, and nearly half a million women die from it annually.

In this trial the participants were randomly selected to either receive exemestane or a placebo. 11 of those in the exemestane group developed invasive breast cancers, compared to 32 in the placebo group. The percentage of patients with precursor lesions was also significantly lower in the exemestane group.

Dr. Goss explained that exemestane has fewer serious side effects compared to tamoxifen. Tamoxifen increases the patients risk of having a stroke, developing cataracts, and uterine cancer.

Compared to tamoxifen, exemestane had milder side effects in general. Although exemestane slightly increases low bone density (osteopenia) risk, it was not enough to cause osteoporosis. Patients on exemestane also experienced fatigue, insomnia, sweating and hot flashes.

Dr. Goss added that nobody yet knows how long a patient would have to take exemestane. However, for post-menopausal women exemestane definitely merits consideration for breast cancer prevention.

Dr. Goss added that there was no dangerous build-up of toxicity from exemestane after five years.

Aromasin’s patent protection expired on 1st April this year. In 2010 it generated $483 million’s worth of income for Pfizer, its makers and marketers.

Aromasin was originally approved by the FDA to treat post-menopausal patients with advanced breast cancer who had been on tamoxifen for two or three years. It is also prescribed for women for whom tamoxifen was not effective.

Breast cancers usually start in the lobules or the ducts. Lobules are the milk-producing glands, while the ducts are the passages that drain milk from the lobules to the nipple.

Non-invasive breast cancer – also known as carcinoma in situ (in the same place) or pre-cancers, the cancer stays within either the milk ducts or the lobules in the breast. They do not invade (grow into) normal tissues within the breast or beyond it.

Invasive breast cancer – the cancer grows into normal, healthy tissues.

The majority of breast cancers are invasive.

Written by Christian Nordqvist