Test  Developed: Who Needs Tamoxifen

Clue Found to Breast Cancer Drug Resistance

LONDON (Reuters) - Scientists have discovered why some breast cancer patients do not respond to the drug tamoxifen, in a finding that could improve treatment and save lives from the disease that afflicts a million women worldwide each year.

Tamoxifen is the most widely prescribed drug for breast cancer and has been credited with improving survival of women with the illness.

Breast cancer patients with tumors that use estrogen to grow are routinely given the drug, but it does not work in all women.

Researchers at Cancer Research UK said on Wednesday they have found a change in a molecule that explains why, and they are developing a standard test to detect which patients will not respond to the drug and would benefit from alternative treatments.

"When you give patients tamoxifen the only way of measuring response is by seeing whether the tumor continues to grow or not. If you can determine how the patient will respond you could put them on tamoxifen or a more appropriate treatment. So it (the finding) will likely save lives," said Dr. Simak Ali of Imperial College in London.

Tamoxifen works by neutralizing the action of the hormone oestrogen, which stimulates breast tumor growth. It blocks the function of the oestrogen receptor (ER), which around half of breast tumors rely on for their growth.

Studies have shown that it is effective in treating early and advanced breast cancer, particularly in women older than 50 who are most likely to develop the disease. But the drug can also increase the risk of a rare form of cancer of the uterus.

After studying the ER, Ali and his team noticed that part of the molecule is altered in some women and instead of being blocked by tamoxifen, it becomes more active. Their research is published in the journal Oncogene.

"Chemical alteration seems to switch the ER molecule into a completely different state, in which it becomes immune to the inhibitory effects of tamoxifen," said Ali.

"It's important that we learn to identify women who are not going to respond to the drug."

[07/26/2002; Reuters Health]

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