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‘Positive’ Tumors That Aren’t
By Marilynn Larkin
Certain breast cancer tumors initially test positive for estrogen receptors (ERs)—which in a postmenopausal woman would indicate the need for hormonal therapy, such as an aromatase inhibitor (AI). Then, for reasons doctors don’t yet understand, the tumors become estrogen receptor-negative and continue to grow despite the therapy—a development noticeable on a patient’s follow-up scans. This transformation is associated with greater recurrence risk and poor outcomes.
Doctors haven’t been able to predict which ER-positive patients have these deceptive tumors. Now they may be able to, says Matthew Ellis, MD, PhD, of the Washington University School of Medicine’s Siteman Cancer Center in St. Louis. Ellis and colleagues were able to identify a unique genetic signature of certain ER-positive tumors. They measured the expression of this signature in a group of women before treatment with the AI letrozole (Femara), then again one and four months after they started taking the drug. The team discovered that after AI treatment began, certain tumors that had initially been positive for estrogen receptors lost a significant number of those receptors, transitioning to an ER-negative state.
The test for the gene signature should be available later this year and will be validated in clinical trials. Ellis believes that it could become standard for women with this gene signature to have their tumors’ estrogen receptor levels monitored as soon as one month after starting AI therapy, to determine whether a course of treatment for ER-negative cancer would be more appropriate.
