from the August 22, 2011 issue of Connect

Javaid Iqbal

A systematic review performed by scientists at Women’s College Research Institute has shed light on the use of a drug that’s long been known to substantially lower the risk of breast cancer in high-risk women: tamoxifen.

For years, tamoxifen has been used to treat recovering breast cancer patients, to prevent cancer recurrence.

After two major breast cancer prevention studies showed that tamoxifen reduced the occurrence of breast cancer by almost 50 per cent in women at high risk of developing it, the Food and Drug Administration approved it as a preventive therapy in these women.

Women who don’t have BRCA1/2 mutations but who have a strong family history of breast cancer have a 10 to 25 per cent chance of developing breast cancer during their lifetime. But only four to five per cent of these women choose to take tamoxifen as a preventive agent, a surprisingly low number considering its enormous benefits.

“We believe it’s because of misconceptions about the drug’s safety and side-effects,” says Javaid Iqbal, a Women’s College scientist-in-training who works with Dr. Steven Narod in the Familial Breast Cancer Research Unit. “Patients and physicians have a lingering fear of the drug’s side-effects, because of insufficient information and understanding of what the numbers really mean.”

Iqbal is referring to tamoxifen’s reputation for increasing the risk of invasive cancers of the uterus, as well as blood clots in the legs and lungs. However, when Iqbal led a systematic review examining published data on tamoxifen, his team found that in premenopausal women, the risks of serious side-effects were low. In fact, they were statistically insignificant.

“If a premenopausal woman opts to take tamoxifen for breast cancer prevention, her chances of developing these serious side-effects are less than one per cent,” says Iqbal.

“Many high-risk women would find that risk more than acceptable, when you consider the drug offers a 50 per cent reduction in breast cancer occurrence.”

The confusion started because, out of the four tamoxifen breast cancer prevention studies, only one study reported the data on serious side-effects according to the participants’ menopausal status. Also, it was not clear from the published data whether these side-effects persisted beyond the active phase of treatment.

“We believe people have had difficulty understanding the results of many of the studies,” says Iqbal. “However we found that the side-effects of tamoxifen decrease or vanish in the followup phase when the treatment is completed. We also found that side-effects are lower in premenopausal women.”

To clearly illustrate the numbers, the Women’s College team decided to analyze the data on premenopausal women according to the phase of their treatment. Then they created a unique table displaying detailed information on the rates and risks of complications during both the active and the followup phases of treatment.

“If you look at this table, the picture is very clear,” says Iqbal, explaining that “to our knowledge, no one will find this information displayed this way in any other publication.”

By clarifying the lingering misconceptions about tamoxifen’s safety, Iqbal hopes that his work will ease women’s and physicians’ concerns about a drug that can dramatically lower breast cancer risk in certain women.

“We hope to rescue the reputation of this very useful drug,” says Iqbal. “Especially because it’s the only feasible preventive option for premenopausal women at an increased risk of breast cancer.”