Background: Ami, an EGFR-MET bispecific antibody, is approved for pts with advanced EGFR exon 20 insertion non-small cell lung cancer after progression on platinum-based chemotherapy. Intravenous (IV) delivery is associated with infusion-related reactions (IRRs) in 67% of pts, requiring splitting the first dose over 2 days (Park Ann Oncol 2021;32[suppl_5]:S981). PALOMA (NCT04606381) is an ongoing phase 1b dose escalation study of subcutaneous (SC) ami ± rHuPH20 (a hyaluronidase that aids SC agent absorption) in pts with advanced solid tumors who may benefit from EGFR- or MET-directed therapy. Preliminary results showed SC ami was well tolerated, improved time and ease of administration, and meaningfully reduced IRRs (Krebs Cancer Res 2022;82:12_Supplement, CT198). We present updated safety results and identification of the recommended phase 2 dose (RP2D) for ami SC Q2W administration. Methods: PALOMA enrolled pts with various advanced solid tumors. Objectives were to evaluate administration feasibility, safety, and PK of low and high concentration formulations of ami SC (50 mg/mL ami ± rHuPH20 [Part 1; Cohorts 1a/b] and 160 mg/mL ami ± rHuPH20 [Part 2; Cohorts 2a/b, Cohort 3a, Cohort 5a]). Cohorts 1a/b and 2a/b received 1050 mg (1400 mg, ≥80 kg), Cohort 3a received 1600 mg (2240 mg, ≥80 kg), and Cohort 5a received 2560 mg (3360 mg, ≥80 kg). Cohorts 1-3 were dosed weekly for the first 4 weeks and Q2W thereafter. Cohort 5a was dosed weekly for the first 3 weeks and Q3W thereafter. Results: As of Jan 3, 2023, 81 pts were enrolled (16 pts in Part 1, 65 pts in Part 2) and majority had NSCLC (71; 88%). Median age was 64 years, 44 (54%) pts were female, and most pts were White (44; 54%) or Asian (34; 42%). Across all doses, IRRs were reported by 13 (16%) pts; all of grade 1-2. The most frequent manifestations of IRRs were chills (7%), pyrexia (7%), and asymptomatic tachycardia (4%). Treatment-emergent AEs (TEAEs) of rash were reported by 59 (73%) pts, with no grade ≥3. In total, 3 (4%) pts discontinued ami SC due to toxicity (2 pneumonitis, 1 asthenia). Grade ≥3 related TEAEs were reported by 3 (4%) pts (hypoalbuminemia, lymphopenia, hypertension). Full ami SC dosing on day 1 was feasible (≤7 min), obviating the need for split dosing. PK analysis confirmed that ami SC 1600 mg (2240 mg, ≥80 kg) Q2W resulted in similar exposure to the approved IV dose (1050 mg [1400 mg, ≥80 kg] Q2W). Compared to IV, ami SC resulted in lower C_max and equal or higher C_trough and AUC_0-336h at Cycles 2 and 4. Based on these data, ami SC 1600 mg (2240 mg, ≥80 kg) was selected as the RP2D for ami SC Q2W administration. Conclusions: Ami SC was well tolerated with meaningful reductions in administration time and TEAEs. Ami SC provided a quantitative and qualitative improvement in the symptoms of IRRs vs historical IV rates. The identified RP2D for ami SC on the Q2W schedule achieved similar exposure as the approved IV dose. Clinical trial information: NCT04606381.