205P Trastuzumab biosimilar (TB) in combination with pertuzumab (P) and chemotherapy (ct) in HER2 positive, metastatic breast cancer (mBC): Efficacy and safety

TB in Europe are available since 2018 and widely prescribed. However, no data have ever been reported regarding their efficacy and tolerance in combination with pertuzumab and chemotherap. Methodology: The observational PErtuzumab – TRAstuzumab (PETRA) study prospectively included patients with Her 2-positive MBC receiving CT + P + TB, whatever the EMA-approved product. The main objectives were safety and efficacy. Between Feb 3, 2021 and Jul 31, 2023, 110 patients from 21 centers were included: median age 58.5 [50.0 – 72.0], PS 0: 38.7 %, 1: 53.8 %, 2: 7.5 % ; median BMI 24.9 [21.1 – 29] ; median baseline LVEF (%): 65 [60.5 – 69] ; Her 2 +++: 77.1 %, Her 2 ++ and FISH +: 22.9% ; HR +: 63.6 % ; de novo metastatic: 40 % ; visceral mets: 56.4 % ; CNS involvement: 13.6 % ; previous (neo)adjuvant trastuzumab: 22.7 % ; (neo)adjuvant chemotherapy: 36.4 %. TB was TRAZIMERA® in 38 pts (34.5 %), ONTRUZANT® in 26 (23.6 %), HERZUMA® in 23 (20.9 %), OGIVRI® in 19 (17.3%) and KANJINTI® in 4 (3.6 %). Chemotherapy was weekly paclitaxel in 80.0 % of pts, docetaxel in 16.4 %, vinorelbine in 3.6 %. Median follow-up was 5.7 months [4.5 – 6.3]. Median number of TB cycles was 7.0 [6.0 – 9.0]. DCR was 80.9 %. ORR: 70 %, CR: 35.5 %. Three non TB related deaths (5.5 %) and 18 tumor progressions (16.4 %) were observed. 6-months PFS and OS probabilities were 0.7 [0.55 – 0.81] and 0.97 [0.92 – 0.99]. Grade 1-2 side effects were observed in 60.9 % of pts, grade ≥ 3 in 35.5 %. TB discontinuation due to toxicity occurred in 2 pts (1.8 %). There were 15 (13.6 %) pts with hypersensitivity reactions (grade 3: 5/15 = 33 %), 7 pts with cutaneous rash (Grade 3: 1/7 = 14.3 %). Thirty –six pts (32.7 %) experienced diarrhea (grade 3: 7/36 = 19.4 %). The rate of febrile neutropenia was 6.4 %. One pt experienced grade 4 interstitial lung disease possibly related to trastuzumab. Median difference in LVEF (%) vs baseline at 3 and 6 months were - 2 (-5.0 – 1.0) and 0.0 (-7.0 – 1.0). Two pts experienced grade 3 and 4 CHF, respectively. Efficacy and tolerance of TB appears comparable to HERCEPTIN in the metastatic setting, as reported in previous clinical trials.