WEDNESDAY, Dec. 8, 2004 (HealthDayNews) -- A newer drug called anastrozole could replace tamoxifen as the standard drug for postmenopausal breast cancer patients whose cancer is fueled by estrogen, a new study finds.
Anastrozole was found significantly more effective than tamoxifen in increasing the number of women who remained free of cancer, lengthening the time before cancer recurred in many patients, and reducing the incidence of cancer spreading, particularly to the other breast.
The results were so significant that the authors of the international study recommend replacing tamoxifen with anastrozole as the drug given to women for five years following their initial cancer treatment.
Anastrozole, brand name Arimidex, is part of a class of drugs called aromatase inhibitors.
"Results from studies suggest that it is reasonable to switch patients currently on tamoxifen to an aromatase inhibitor," wrote the authors of the study, which was led by Anthony Howell, a professor at Christie Hospital NHS Trust, in Manchester, England.
However, some cancer experts note that aromatase inhibitors can come with significant side effects, including increased risk of osteoporosis.
The study findings were presented Wednesday at the San Antonio Breast Cancer Symposium in Texas, and appear in the online edition of The Lancet.
Currently, postmenopausal women whose breast cancer is hormone-receptor-positive -- approximately three-quarters of all patients -- take tamoxifen for five years after their breast cancer surgery. The drug blunts estrogen's ability to fuel cancer growth.
Anastrozole prevents estrogen from being produced in the first place, according to the American Cancer Society. It is often prescribed for women following their tamoxifen therapy.
But the researchers behind the new study found that prescribing anastrozole rather than tamoxifen immediately after surgery significantly improved results for patients.
The study included nearly 10,000 postmenopausal women who had been diagnosed with localized breast cancer -- cancer that has not spread to the lymph nodes -- and treated with surgery. The women were divided into three groups: those who took tamoxifen, those who took anastrozole and those who took both drugs for five years following their initial treatment. Three years into the study, this last group was disbanded because the treatment was not effective.
After five years, researchers found these benefits for those women who took anastrozole instead of tamoxifen: a 10 percent increase in the number of patients who remained disease-free; a 20 percent increase in the overall time until there was a recurrence of disease; a 40 percent reduction in the spread of cancer to the other breast, and 14 percent reduction in the spread of cancer to other sites in the body.
In addition, compliance rates were higher for those women taking anastrozole compared to tamoxifen. And anastrozole produced fewer side effects, although bone fractures and joint pain were more common than among women given tamoxifen, the study found.
The study authors noted that tamoxifen has been shown to reduce by 50 percent the spread of cancer to the other breast. So their findings suggest that anastrozole could prevent 70 percent to 80 percent of these cancer recurrences in women with hormone-receptor-positive breast cancer.
The study did not show significant improvement in overall survival rates among those who took anastrozole compared to those who took tamoxifen. But, the researchers said, more time is needed to determine whether anastrozole will produce better long-term survival rates.
Dr. Otis W. Brawley, professor of oncology at Emory University's Winship Cancer Institute in Atlanta, said, "This is the strongest of the studies I've seen so far that aromatase inhibitors are more effective than tamoxifen, and it will sway a lot of people. But the problem is that aromatose inhibitors cause significant osteoporosis, and one worries that you might be buying a woman worse problems down the road."
Another issue, Brawley added, is the higher cost of aromatose inhibitors compared to tamoxifen. That cost differential might lead some women to stop taking the drug before the therapy is completed.
Meanwhile, in other news reported at the San Antonio conference, a study of 1,477 breast cancer patients found that many postmenopausal women with hormone-receptor-positive breast cancer may be under-treated if they don't get chemotherapy along with hormonal therapy, such as tamoxifen.
Further, long-term survival is higher when the chemotherapy precedes the hormone therapy rather than when the two are given concurrently, according to the researchers, from Loyola University Chicago Stritch School of Medicine.
Ten-year disease-free-survival estimates were 48 percent for those who took tamoxifen alone, 53 percent for those who had both treatments at the same time and 60 percent for sequential therapy, the authors reported.
Also presented at the conference were the results of a novel gene-based therapy that, when performed before breast cancer surgery, reduced tumor size by nearly 80 percent.
About half of patients with locally advanced breast cancer have mutations in a gene designated p53, which plays a critical role in suppressing cancer development. In the study, doctors injected p53 protein directly into the tumors of 12 patients with locally advanced breast cancer. All the tumors were quite large -- an average of 8 centimeters, which is about the size of a silver dollar. The patients then received a course of chemotherapy.
As a result of the combination therapy, all the tumors shrank by more than half, so that many of the patients could choose lumpectomy instead of mastectomy to remove their tumors, the researchers said. Tumors in the patients' lymph nodes also decreased in size.
The study was done by researchers at the University of Texas M.D. Anderson Cancer Center.
The American Cancer Society has more on treatments for breast cancer.