To Örebro University

Background: Neoadjuvant treatment with Trastuzumab-emtansine was associated with similar rates of pathological complete remission (pCR) as standard therapy withd ocetaxel, trastuzumab and pertuzumab in the PREDIX HER2 trial. Here, results of event-free survival (EFS), and pCR rates in key clinical-pathological subgroups and biomarkers including the abundance of stromal tumor infiltrating lymphocytes (TILs) are presented.

Methods: PREDIX HER2 is a randomized, multicenter, open-label, phase 2 study involving 9 Swedish sites. Patients with HER2 positive breast cancer, verified by ISH, T>20 mm and/or verified lymph node metastases were randomized to six three-weekly courses of either docetaxel, trastuzumab SC and pertuzumab (group A), or trastuzumab emtansine (T-DM1, group B). Switch of treatment to the opposite arm was allowed in case of lack of response or severe toxicity. Radiological evaluation included 18F-FDG PET/CT. Patients in both groups received adjuvant chemotherapy with epirubicin and cyclophosphamide. TILs were evaluated using standard methodology, median 10%.

Results: In total 197 pts. were evaluable, 99 in group A, and 98 in group B. pCR (ypT0/is ypN0) was achieved in 90 pts, 45.7%, with no significant difference between the two treatment groups. pCR rates were lower in the group of patients with hormone receptor (HR)epositive compared with HR-negative tumors but similar in both treatment groups. pCR rates did not differ between the two treatments in subgroups defined by age, menopausal status, tumor grade, T size, node status, HR-status, HER2 status and Ki67. Progressive disease was observed in 3 pts. (3%) during treatment with T-DM1, none in group A. After a median follow-up of 2.4 years 13 EFS events occurred, with no significant differences between the treatment groups. The presence of 10% TILs predicted pCR significantly (p¼0.009), similar in both treatment groups. We also found that a decrease of SUVmax by more than 80% was highly predictive of pCR. HRQoL was significantly better in pts. receiving T-DM1.

Conclusions: Our data suggest that neoadjuvant T-DM1 may be as effective as standard neoadjuvant treatment in all clinical subgroups evaluated. Both TILs and PET/CT showed potential to predict pCR.

Clinical trial identification: NCT02568839.