According to a study published online Wednesday in the journal Nature, scientists found the mechanism underlying why some women with breast cancer develop resistance to tamoxifen. “For the first time, we’ve started to identify what the key and critical factors are that can cause drug resistance,” stated lead investigator Jason Carroll.

The researchers found that tamoxifen works by switching off the ErbB2 gene with the Pax2 protein, and that resistance to the drug occurs when Pax2 fails to keep ErbB2 inactivated. The investigators examined 109 breast cancer tumours, all of which had been treated with tamoxifen. The results showed that 68 of the tumours were Pax2-positive and 41 were Pax2-negative. The findings also demonstrated that women with Pax2-positive tumours had a “significantly improved” chance of survival without cancer recurrence than those who had Pax2-negative tumours.

Carroll commented that “the new discovery will help us identify women most likely to respond to tamoxifen and, more importantly, those who will not for whom we can develop alternative therapies.” The researcher noted that the data suggest that some patients should potentially be treated directly with drugs such as Genentech’s Herceptin or AstraZeneca’s Arimidex, and that the findings should be duplicated in larger studies.

Source: FirstWord

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