Determinants of biomarker testing and treatment selection by oncologists caring for patients (pts) with gastric or gastroesophageal junction (G/GEJ) adenocarcinoma (AC).

Abstract

453 Background: Biomarker testing helps guide targeted therapy in G/GEJ AC; however, with no standardized approach, treatment selection varies by physician. Using an implementation science approach, we explored factors that determine whether oncologists: 1) order biomarker tests and 2) select biomarker-based treatments. Methods: We conducted semi-structured, web-assisted telephone interviews (March 2025) with 15 US-based oncologists (≥50% time in direct pt care), who treated ≥1 new pts with G/GEJ AC in the preceding month. Interview guides were designed using the Theoretical Domains Framework (TDF) to explore behavioral determinants. We first coded physicians’ statements deductively using the 11 TDF domains then coded inductively within each domain to identify domain-specific themes. Key domains and associated barriers/facilitators were prioritized based on frequency, impact on target behavior, and presence of conflicting beliefs. Domains with high-priority themes were mapped to validated behavior change techniques (BCTs). Results: Oncologists had a mean of 18 years’ experience (range: 4–26) and saw a mean of 13 new pts (range: 2–50) with G/GEJ AC. Oncologists routinely ordered biomarker tests, supported by a strong sense of professional responsibility and institutional systems; however, >50% had difficulty keeping current on biomarkers and used varying prioritization approaches – clinical evidence, experience, or pt characteristics. Five domains influenced test ordering: social/professional role; beliefs about consequences; environmental context; knowledge; motivations/goals/priorities. For treatment selection, 3 domains were key: knowledge; memory, attention, decision processes; skills. Table summarizes key domains, barriers/facilitators, and linked BCTs to improve outcomes. Conclusions: Oncologists routinely order biomarker tests; however, knowledge gaps and decision complexity hinder consistent biomarker-based treatment selection. Targeted BCTs may enhance facilitators and address barriers to optimize pt care. Key domains Barriers Facilitators BCTs Ordering tests Social/professional role – Responsibility Peer support and encouragement Beliefs about consequences – Regret missing treatment options Persuasion; feedback Environment External factors Clinical integration Environmental changes Knowledge Staying up to date Credible sources Information; educational outreach Motivations/ goals/priorities Lack of urgency Sense of urgency Self-evaluation; prompts/cues Biomarker-based treatment selection Knowledge of biomarkers Incomplete Strong Information; outcomes Memory, attention, decision No standardized approach Clinical evidence Decision aids; monitoring Skills Uncertainty interpreting results Ease in applying findings Peer demonstration; goal setting