Background: TAPUR is a phase II basket study evaluating antitumor activity of commercially available targeted agents in pts with advanced cancers with genomic alterations. Results in a cohort of pts with BTC with ERBB2/3 amp, oe, or mut treated with P+T are reported. Methods: Eligible pts had advanced BTC, no standard treatment (tx) options, measurable disease, ECOG Performance Status (PS) 0-2, and adequate organ function. Genomic testing was done in CLIA-certified, CAP-accredited labs. Dosing of P was 840 mg IV over 60 minutes (m), then 420 mg IV over 30-60 m Q3 weeks (wks); T was 8 mg/kg IV over 90 m, then 6 mg/kg IV over 30-60 m Q3 wks until disease progression. Primary end point was disease control (DC), defined as complete (CR) or partial (PR) response per RECIST v. 1.1, or stable disease (SD) at 16+ wks (SD16+). Simon 2-stage design tested the null DC rate of 15% vs. 35% (power = 0.85; α = 0.10). If ≥2 of 10 pts in stage 1 has DC, 18 more pts are enrolled; otherwise, cohort is closed for futility. If ≥7 of 28 pts has DC, the null DC rate is rejected. Secondary end points were progression-free survival (PFS), overall survival (OS), duration of response (DOR), duration of SD and safety. DOR is defined as time from pt’s first documented objective response (OR) to progressive disease (PD). Duration of SD is defined as time from start of tx to PD. Results: 29 pts with BTC (15 gallbladder (GB), 11 biliary duct (BD), 3 ampulla of Vater) and ERBB2/3 amp, oe, or mut were enrolled from Feb 2017 to Jan 2022. Median (med) age was 66 years (yrs) (range, 34-83 yrs). 66% of pts were female; 52% were White, 21% were Black/African American, 10% were Asian/Asian American; 83% were not Hispanic or Latino. 83% of pts had ECOG PS 0-1 and 48% had ≥3 prior systemic regimens. 1 pt was not evaluable and excluded from efficacy analysis. The table shows efficacy outcomes. 1 pt had CR (GB; ERBB2 amp; DOR: 71.1 wks), 8 pts had PR (6 GB/2 BD; 5 ERBB2 amp; 2 ERBB2 mut; 1 ERBB3 mut/ERBB2 amp; med DOR: 30.4 wks (4.4 to 68.9 wks)) and 2 pts had SD16+. 4 pts with a KRAS mut did not achieve OR or SD16+. 4 pts had a Grade 3 drug-related adverse or serious adverse event (SAE): anemia, diarrhea, infusion related reaction (SAE), and fatigue. Conclusions: P+T demonstrated antitumor activity in pts with advanced BTC with ERBB2/3 alterations. These data, along with results previously reported by other studies, support continued study of P+T in pts with ERBB2 amplified BTC tumors. Clinical trial information: NCT02693535.