A new class of drugs may prove to be the next powerful weapon in the fight against breast cancer.

While one of the most popular treatments for breast cancer is the use of the drug tamoxifen, four large clinical trials have shown that compounds called aromatase inhibitors have a slight advantage — 4 to 5 percent — over tamoxifen in preventing tumor recurrence, said Daniel Hayes, clinical director of the University’s breast oncology program.

This advantage is small but significant. In earlier trials, AIs were successful in patients whose cancer had already metastasized, or spread to other parts of the body. These new trials suggest that AIs may be useful in preventing the spread from occurring.

According to the American Cancer Society, breast cancer kills more than 40,000 people each year in the United States. Although incidences have been increasing over the last 50 or 60 years, mortality has been dropping “relatively steeply” in the United States, Hayes said.

One reason for this drop is adjuvant therapy, which supplements the treatment of the breast with treatment of the entire body. Aside from chemotherapy, there is also hormone therapy, which targets hormones cancer cells need to grow. Treatment with tamoxifen and AIs are examples of therapy that target the hormone estrogen. More than half of breast cancers require estrogen, and these cancer cells have estrogen receptors, which are detectable by doctors.

“If you think of a cancer cell like an automobile,” Hayes said, “the estrogen receptor is like a gas tank, and estrogen is like gasoline.”

Tamoxifen, which blocks the estrogen receptor, is like putting water in the gas tank to screw up the engine, Hayes said.

On the other hand, AIs — which include Arimidex, Aromasin and Femara — act at an earlier point in the process — they stop the estrogen from being made in the first place. Because of their unique point of attack, they are only effective in postmenopausal women.

Hayes said the advantage of AIs is pretty small, and so far, they have seen no difference in survival. They do, however, prevent tumor recurrence as well as or better than tamoxifen. By stopping the spread of cancer to the rest of the body — as well as keeping it from coming back – they increase the patients’ quality of life. This may lead to an increase in survival, but a difference may not be apparent after the short duration of the study.

For a patient with a good prognosis and some sign of osteoporosis, Hayes recommends tamoxifen because AIs elevate the risk of osteoporosis. For a patient with a bad prognosis and no sign of osteoporosis, however, Hayes thinks AIs are a good choice because of their effectiveness in preventing tumor recurrence and metastasis.

Despite the increased risk of osteoporosis, AIs lower the risk of uterine cancer and blood clots, Hayes said.

Tamoxifen has been around for thirty years. “I think we know everything bad about tamoxifen that we’re gonna know,” Hayes said. AIs, on the other hand, have only been around for ten years, and the early trials were on patients who already had metastatic cancers.

“We may see things from these drugs that we don’t know about in the next five or ten years,” Hayes said.


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