Safety and clinical evaluation of dual inhibition with pertuzumab and trastuzumab in HER-2-positive breast cancer patients.

e12520 Background: The addition of Herceptin to standard chemotherapy improved survival in patients with Her-2-positive breast cancer in neoadjuvant, adjuvant and metastatic setting. In higher tumor stage, the addition of pertuzumab is now standard of care and associated with a favorable toxicity profile. The purpose of this study was to evaluate the safety and efficacy of the biosimilar trastuzumab-dttb in combination with pertuzumab in Her-2-positive breast cancer patients. Methods: Thirty-five female patients with Her-2-positive breast cancer treated at the Division of Oncology at the Medical University of Graz between September 2018 and August 2019 were included. Summary measures are reported as medians 25th– 75thpercentile for continuous variables and as absolute frequencies (%) for count data. Results: Thirty-five patients received a median of four [3-7] cycles of trastuzumab-dttb plus pertuzumab. The median cumulative trastuzumab-dttb dose was 1904mg [1560-2640] and the median cumulative pertuzumab dose was 2100mg [1680-3360]. All patients had a normal baseline LVEF (> 50%) prior to the initiation of trastuzumab-dttb plus pertuzumab treatment with a median LVEF of 60% [60-65]. At completion of trastuzumab-dttb plus pertuzumab treatment (or in case of ongoing therapy the last EF assessment), the median LVEF was 60.0 % [58-62]. 21 patients had a median absolute LVEF decline of 1% -5-0], corresponding to a median percent change of 1.7 percent points [-7.7-0]. Two patients (5.7%) had a LVEF reduction ≤50%. None of the patients had a decline in LVEF of ≥ 10 %. In 8 patients, a switch from Herceptin to trastuzumab-dttb was tolerated well and these were also included in the analyses. In only two palliative patients, pertuzumab was either interrupted or stopped due to diarrhea and appetite loss, while trastuzumab-dttb was ongoing. 24 of 35 patients (69%) were treated with trastuzumab-dttb plus pertuzumab in the neoadjuvant setting. Two of these patients were treated for local relapse and were excluded for efficacy assessment. Of the remaining 22 patients, 11 patients achieved a pCR (ypT0/ypTis and ypN0). Conclusions: In these series of Her-2-positive breast cancer patients, the combination of trastuzumab-dttb/pertuzumab was consistent with the known safety and efficacy profile of Herceptin/pertuzumab.