ESTES PARK, COLO. – Primary care physicians appear to have dropped the ball when it comes to primary chemoprevention of breast cancer, studies suggest.
Chemoprevention is enormously underutilized. An estimated 2 million American premenopausal women are candidates for primary chemoprevention of breast cancer with tamoxifen, an agent shown to reduce their risk by 50%. Yet only 4% of them are on this safe and generally well-tolerated estrogen receptor antagonist, Dr. Jennifer R. Diamond said at an update in internal medicine sponsored by the University of Colorado at Denver.
Dr. Jennifer R. Diamond
Moreover, when she informally polled her audience at the outset of her talk, 93% indicated via electronic clicker that they were not comfortable with chemoprevention for breast cancer and didn’t commonly use it in appropriately selected patients in their practice.
"The most common side effect I see with tamoxifen for primary chemoprevention is hot flashes. But many young women will do fine. They don’t have any problems. And the opportunity to reduce the risk of breast cancer by 50% in these young women makes this an option I think you really need to be offering to young women" who are at increased risk for breast cancer, said Dr. Diamond, a medical oncologist at the university.
Nearly 230,000 American women will receive a new diagnosis of breast cancer in 2012. More than 39,000 women will die this year from the malignancy.
Secondary chemoprevention is most effective for women who have been diagnosed with lobular carcinoma in situ. The recommendation to embark on secondary chemoprevention usually comes from the patient’s medical oncologist.
In contrast, most candidates for primary chemoprevention have never seen a medical oncologist. Thus, primary chemoprevention falls within the bailiwick of primary care physicians. The latest guidelines from the National Comprehensive Cancer Network identify appropriate candidates for primary chemoprevention as women who have a first-degree relative with breast or ovarian cancer; a history of thoracic irradiation; mutations predisposing to breast cancer; or a 5-year risk of breast cancer of at least 1.7% according to the breast cancer risk assessment tool (the Gail model).
A 5-year risk of 1.7% or greater is not a high bar. It equates on the Gail model to being 65 years old without additional risk factors. "You’ll find that many of your patients are candidates," Dr. Diamond predicted.
Two options are available for primary chemoprevention; the determining factor as to which is best in a given high-risk individual is menopausal status. Premenopausal women can benefit from 5 years of oral tamoxifen at 20 mg/day. In postmenopausal women, however, exemestane (Aromasin), an aromatase inhibitor, is the safer, better choice, even though the drug’s use in chemoprevention is, for now, off label, she continued.
The oft-cited figure of a 50% reduction in breast cancer risk conferred by tamoxifen comes from the landmark randomized, placebo-controlled NSABP (National Surgical Adjuvant Breast and Bowel Project) P-1 trial (J. Natl. Cancer Inst. 1998;90:1371-88). The protective effect continued after treatment ended. The number needed to treat at 20 mg/day for 5 years in order to prevent one additional case of breast cancer was calculated at 95 in 5 years and 56 in 10 years. Women younger than age 50 years experienced no excess risk of serious adverse events.
"The risks of venous thromboembolism and endometrial cancer are what we all worry about with tamoxifen, but they’re actually incredibly uncommon" in women younger than age 50, she said. "I don’t recommend that you use tamoxifen in your postmenopausal women; that’s where you get into trouble with endometrial cancer and thromboembolic events. I believe that you can safely use tamoxifen in premenopausal women without a significantly increased risk of thromboembolic events. I equate the risk to that of birth control pills."
Raloxifene joins tamoxifen as the only other proved drug with Food and Drug Administration approval for primary breast cancer chemoprevention. The NSABP STAR (Study of Tamoxifen and Raloxifene) trial showed that the two medications are equivalent for prevention of invasive breast cancer, but that raloxifene is less effective in preventing ductal carcinoma in situ (JAMA 2006;295:2727-41). For this reason, Dr. Diamond and her colleagues don’t use it.
For postmenopausal women who are candidates for primary chemoprevention, Dr. Diamond said that she turns to exemestane on the basis of the National Cancer Institute of Canada CTG MAP-3 trial, which showed a 65% reduction in the annual incidence of breast cancer with 5 years of the aromatase inhibitor, compared with placebo. (N. Engl. J. Med. 2011;364:2381-91).
The number needed to treat with exemestane at 25 mg/day for 5 years in order to prevent one invasive breast cancer was 94 in 3 years and 26 in 5 years.