A recent study from MD Anderson Cancer Center looked at a group of women with breast cancers that tested positive for HER2 over-expression who received neoadjuvant chemotherapy.  Of the women who still had residual invasive cancer in their breast following their surgery, approximately 30% of them had cancers that were now HER2 negative.

We performed a similar study a few years ago that we presented at the United States and Canadian Academy of Pathology.  We found that 22% of our patients that were HER2 positive prior to neoadjuvant chemotherapy were HER2 negative following surgery.  We also found changes in estrogen and progesterone receptor status following neoadjuvant chemotherapy.

What does this mean? It could mean that some cancers are made up of HER2 positive and HER2 negative cells and the HER2 negative cells survive the chemotherapy. Or could cancer cells change over time and go from positive to negative?  More research needs to be done to figure this out because it could have an impact on what type of treatment a patient receives if her cancer changes following neoadjuvant chemotherapy.

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