Research backs drug raloxifene in battle against breast cancer
April 20, 2010 4:00 AM
Kathleen Mausteller, of Shaler, participated in a major national study of two breast cancer prevention drugs.
By Mark Roth Pittsburgh Post-Gazette
When Kathleen Mausteller learned she had a chance to join a major breast cancer prevention study in 1999, she jumped at the chance.
Her older sister had breast cancer. Her younger sister had died of it. So had two aunts and her grandmother.
So, even though the Shaler woman lived a healthy lifestyle and had never missed work because of illness, she knew the genetic tendencies in her family would have no respect for that.
Today, she has good reason to feel justified in her decision.
Not only is she cancer-free herself, but the latest report on the study she participated in shows that the drug she was taking, raloxifene, is almost as good at preventing breast cancer as its better known cousin, tamoxifen, but has far fewer side effects.
The update of the international Study of Tamoxifen and Raloxifene, known as STAR, was presented Monday at the American Association for Cancer Research meeting in Washington, D.C., by Dr. D. Lawrence Wickerham, an Allegheny General Hospital doctor who is associate director of the National Surgical Adjuvant Breast and Bowel Project, which oversaw the trial.
After tracking more than 19,000 women for nearly seven years, STAR found that raloxifene is 75 percent as good at preventing breast cancer as tamoxifen, but is much less likely to cause endometrial cancer, cataracts and blood clots, Dr. Wickerham said. The study is expected to run for another two years, he said, but at this point, he doesn't expect the final results to differ much from this week's report.
Doctors have been promoting tamoxifen for preventing first-time breast cancer and breast cancer recurrence for several years now, he said in an interview last week, but it's been an uphill battle because of the drug's side effects, particularly cancer of the uterus.
Ms. Mausteller knows about that risk firsthand. Her older sister, who took tamoxifen after treatment for breast cancer in the late 1990s, got uterine cancer a few years ago.
In the meantime, Ms. Mausteller is not only free of cancer, but has suffered no side effects, she said. As an extra benefit, her bones are stronger, too, because raloxifene was originally prescribed to help prevent osteoporosis.
In fact, after taking raloxifene for five years and then stopping it, as the study dictated, she is now back on it again after a bone density test showed she could use the drug's help.
Before she joined STAR, Ms. Mausteller thought briefly about her lifelong aversion to "taking a pill you didn't need, but I felt that for the information they could glean from the study, it was worth it for me and for my daughter and my sister's daughters."
Both tamoxifen and raloxifene work by attaching to the cellular receptors for the female hormone estrogen.
About 75 percent to 80 percent of postmenopausal women who get breast cancer have a type that is sensitive to estrogen, Dr. Wickerham said, and both drugs appear to mitigate that effect by blocking estrogen receptors.
If that's the case, though, why would tamoxifen also lead to endometrial cancer?
The reason, he said, is that these drugs seem to act like anti-estrogen compounds in some tissues, like the breast, but function like weak forms of estrogen in other tissues, such as the uterus or the bone.
In the uterus, that effect is much stronger with tamoxifen, the STAR update showed.
After 81 months, women taking raloxifene had only half the rate of uterine cancer as those taking tamoxifen, and had one-fifth the rate of uterine hyperplasia, which causes extra growth in the lining of the uterus and forces some women to get dilation and curettage, known as a D&C.
Even though tamoxifen's side effects are worse, it has a definite edge over raloxifene on cancer prevention, the study showed. Over several years, it said, tamoxifen appears to lower the incidence of breast cancer in postmenopausal women who are at high risk of the disease by about 50 percent, while raloxifene lowers the incidence by 38 percent.
So, if a woman already has had a hysterectomy and has a family history of breast cancer, tamoxifen might be the drug of choice, Dr. Wickerham said. If she is a younger postmenopausal woman with a family history of breast cancer, and has an intact uterus, raloxifene might be the better option.
The women most likely to benefit from the study's good news, he said, are the half million in the United States already taking raloxifene to help prevent osteoporosis.
"The bottom line," he said, "is that postmenopausal women who have increased risk for breast cancer now have some options to substantially reduce that risk. It will allow us to take a major step forward in making breast cancer a preventable disease."
For Kathleen Mausteller, there is one other benefit from having joined the study.
Even if the 72-year-old were to get breast cancer, she said, the study has allowed her to develop relationships with some of the best cancer specialists in the city.