DR LOVE: That was actually the other thing I was going to ask you about, which of the triple-positive kind of scenario and of course the approval for palbociclib is HER2-negative disease, which kind of seems a little weird to me, but, in any event, we always thought of hormone pathways in HER2, at least clinically, sort of separately. Any reason to think that the benefits that you see by adding on a CDK4/6 inhibitor would be different in a patient who has HER2-positive disease even if they’re on an anti-HER agent?

DR HURVITZ: I think that the hormone pathway in HER2-positive disease makes the disease behave much differently. We see that in the neoadjuvant realm where pathologic complete responses are entirely different for an ER-positive compared to ER-negative, HER2-positive tumor. When you are looking at studies that have done tissue analysis in the neoadjuvant setting, you can see that the biomarkers that seem to predict resistance to chemotherapy tend to be biomarkers and pathways that relate to the hormone pathway. And, as I indicated, the preclinical data indicates that CDK4/6 inhibition should be very effective in HER2-positive breast cancer.

I think in a HER2-positive breast cancer, you need to inhibit the HER2 pathway. But I think you can get a lot more mileage out of also hitting the hormone pathway. And too few studies have been done to look at that clinically. And now I think we’re seeing the design of more trials that are going to look at that clinically.

DR LOVE: So speaking of that, I see you’re part of an interestingly named and spelled trial, “monarch-HER” — monarch is lower-case, HER upper case. Anyhow, it’s a really interesting design….abemaciclib plus trastuzumab with and without fulvestrant. Sara Tolaney is the overall PI. Can you talk a little bit about the thinking and the design of this study?

DR HURVITZ: I was very happy to join this study, because it does test clinically what we’ve shown preclinically. And so when you think about it, only about 20%, at most, patients have HER2-positive disease. And roughly 50% of those also have ER-positive disease. So you’re looking at 10% of all breast cancers qualifying for this study in a very crowded field where we’re giving patients first-line taxane/trastuzumab/pertuzumab and then T-DM1. So accrual, I think everyone is a little concerned about accrual to this study.

But I can tell you that there is a lot of enthusiasm from patients and doctors for this study, because it’s addressing a very critical question, and that is, can we treat patients with ER-positive, HER2-positive metastatic breast cancer in a gentler, more targeted approach that doesn’t involve traditional chemotherapy? So I think her design makes a lot of sense.

DR LOVE: From a clinical point of view, as long as you brought that up, in what situations with metastatic disease will you start out with hormone therapy and anti-HER therapy without chemo?

DR HURVITZ: Rarely to never. I feel that if a woman is quite elderly and quite frail it makes sense, although I may be inclined to use T-DM1 in that particular case. If you look at the TAnDEM study, which looked at anastrozole/trastuzumab versus anastrozole, I think that the results are unimpressive overall. It doesn’t seem that adding endocrine therapy to single-agent HER2-targeted therapy adds a whole lot compared to single-agent HER2-targeted therapy. The EGF3008 study of lapatinib versus lapatinib/letrozole had similarly unimpressive results, in my opinion.

So I think it’s something that I use in a maintenance strategy. So I’ll start patients with the 6 cycles of taxane-based therapy with HP. And then, during the maintenance phase when they’re just getting the HER2-targeted therapy, add in hormonal therapy.

Genomic assays and (neo)adjuvant treatment decision-making

Early-stage breast cancer in the adjuvant and neoadjuvant settings

Management of metastatic breast cancer (mBC)

CDK4/6 inhibitors for the treatment of breast cancer

Checkpoint inhibitors and other novel immunotherapeutic approaches to breast cancer

Triple-negative and BRCA mutation-positive breast cancers