Biomarkers Irrelevant?

Acting as a discussant for the studies, Louis Weiner, MD, said the findings suggest that therapies for HER2-positive breast cancer have become so effective as to render biomarkers irrelevant in some cases.

“The take-home point for me is that we have drugs that work really well,” said Weiner, of the Lombardi Cancer Center at Georgetown University in Washington. “The predictive biomarkers that you might have identified earlier no longer matter because you basically overwhelm the tumor’s defense mechanisms directed against the therapy.”

Responding to a question, Baselga said the results are not practice-changing at this point but have clear implications for the potential importance of the PI3 kinase pathway in making treatment decisions in the future.

“For women with HER2-positive tumors, I think we should start sequencing and checking for the presence of PI3 kinase mutations for a number of reasons,” he said. “You are going to see a number of compounds in clinical trials that show activity against tumors that harbor PI3 kinase mutations. It could be that we will further fragment the field of HER2 positive breast cancer into those that are PI3 kinase positive and negative.”

“If the EMILIA findings are confirmed in a prospective fashion, it could well be that if you have a PI3 kinase-mutant tumor, that an antibody-conjugate could be a good way to deal with that problem,” he added.

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Primary source: American Association for Cancer Research
Source reference: Baselga J et al. “Relationship between tumor biomarkers and efficacy in EMILIA, a phase III study of trastuzumab emtansine (T-DM1) in HER2-positive metastatic breast cancer” AACR 2013; Abstract LB-63.