You’ve been diagnosed with breast cancer. The doctor tells you you’re HER2 positive. What does that mean? And how will it direct your treatment?

Q. I’ve been diagnosed with breast cancer, and while explaining the results of my pathology report, the oncologist told me the cancer is probably “HER-2/neu positive.” What does that mean, exactly?

A. All cells do three things: they grow, they rest, and they repair themselves. Genes inside the chromosomes in your cells regulate their activity,...