New Guidelines For Drugs To Prevent Breast Cancer In High-Risk Women

In 2011, the US National Cancer Institute released an online breast cancer risk assessment tool, which we have linked below. Primarily designed for women who live inside the United States, for which the National Cancer Institute has the most data, the online questionnaire computes a woman's risk of developing invasive breast cancer from answers to just nine questions. But only recently has the National Cancer Institute had suggestions for preventing breast cancer for women whom the online screening test finds high risk.

How high is "high risk" for breast cancer?

Women are considered "high risk" for invasive breast carcinoma if the model predicts chances of more than 1 in 60, or about 1.7%, of developing cancer over a 5-year period. By age 60, essentially all women are at high risk for breast cancer.

What does the model take into account when predicting cancer?

The Gail model, used to create the online questionnaire, considers a woman's age, race, family history of breast cancer, age at puberty, history of pregnancy, and personal history of breast exams to compute risk of developing the disease. The model can only predict the risk of cancer for women who are 35 or older, and because it's based on data collected in the USA, it may not be accurate for women who live in countries where breast cancer is rare, such as most of East Asia. 

The online risk assessment tool is not accurate for predicting recurrence of cancer in women who have already had it, and it's not 100% accurate. It should not be the only basis for making decisions about cancer, just a source of the right questions to discuss with the doctor.

If I am at high risk for breast cancer, is there anything I can do?

There are two drugs that sometimes prevent breast cancer, tamoxifen (Nolvadex) and raloxifene (Evista).

• Tamoxifen has been used for over 20 years to stop the progression of breast cancer in women and as a treatment for breast cancer in men. The FDA approved it for stopping the contralateral breast cancer (spread of cancer from one breast to the other) and for the prevention of estrogen-related breast cancers in 2005.
• Raloxifene reduces the density of the breast, essentially giving cancer less tissue to work with. The drug is also used to prevent osteoporosis, although many post-menopausal women who use it report that it increases the number and severity of hot flashes.

There are limitations in how well these drugs work. Because their mode of action is to make estrogen less available to cancer cells, they only prevent estrogen receptor-positive breast cancer. Tamoxifen increases the risk of blood clot formation and also increases the risk of cataracts as well as increasing the risk of endometrial cancer. Raloxifene also increases the risk of blood clotting, although not as much, and does not increase the risk of endometrial cancer. Both drugs may be more appropriate for women who have had hysterectomies.

How Much Do These Drugs Lower The Risk Of Breast Cancer?

In high-risk women, tamoxifen lowers the risk of breast cancer by about 50%. In the same risk group, raloxifene lowers the risk of breast cancer by about 40%. 

Keep in mind that cutting the "high risk" of breast cancer in half can mean reducing a risk of a little less than 2% to a risk of a little less than 1%. These numbers only apply to women who have not already had the disease. It's primarily women at "higher high risk" that really benefit from the drugs.

Also the drugs are most useful in women who have particularly high risk for cancer. The latest guidelines, issued 24 September 2013, find that among women who have still have the uterus:

• Benefits of tamoxifen outweigh risks only for women who have a 4.5% chance of breast cancer and who are between 50 and 60 years old. Older women usually do not benefit from this drug.
• Benefits of raloxifene outweight risks for women who have a 3.5% chance of breast cancer and who are in their 50's, but only the highest-risk women in their 60's and 70's.

The drugs are slightly more useful in women who do not have a uterus. Among women who have had hysterectomies:

• Benefits of tamoxifen outweigh risks for women who have a 3.5% chance of breast cancer, but only for women who are in their 50's.
• Almost all women who do not have an intact uterus get some net benefits from taking raloxifene, except for lowest-risk women in their 70's.

These may be less effective in Black women than white.

Women who should never use tamoxifen include those who:

• Have been diagnosed with any form of endometrial cancer.
• Have taken or are taking any kind of blood thinner to prevent or treat blood clots.
• Are pregnant or breast feeding.
• Are younger than 35.
• Are older than 60 and average or low risk for breast cancer.
• Smoke, since smoking further increases the risk of blood clots.
• Have or have had high blood pressure or diabetes or who are or have been overweight.
• Are taking any kind of hormone replacement therapy.

Women who should never use raloxifene include those who:

• Have ever had blood clots that required medical treatment.
• Have ever been diagnosed with a coagulation disorder.
• Have ever been diagnosed with any form of endometrial cancer. The increased risk of uterine cancer and endometrial cancer with the use of raloxifene is less than it is with the use of tamoxifen, but it is not zero.
• Who have not gone through menopause.
• Are younger than 35.
• Are older than 60 and at less than high risk for breast cancer.
• Are taking estrogen replacement therapy or any other kind of hormone replacement therapy.

For "average risk" women, the new guidelines confirm, the dangers of the drugs outweigh their benefits in preventing cancer. Doctors have ways of reducing side effects and increasing efficacy of these medications for many women, however, so if you are concerned about your personal risk of breast cancer, see your physician.