Clinical benefit of various HER2-directed regimens in gastrointestinal malignancies: a retrospective cohort study

Background Multiple drugs targeting the human epidermal growth factor receptor-2 (HER2) have shown clinical activity in gastrointestinal (GI) cancers. How to best integrate these various options in clinical practice alongside conventional therapy, however, is unclear. Methods We assessed the clinical outcomes of 103 patients with advanced HER2-altered GI malignancies who received ≥ 1 line of anti-HER2 therapy at our institution between 2010 and 2023. Results Next-generation sequencing (NGS) detected an ERBB2 amplification in 66% (27/41) of tumors that were HER2 + by IHC/ISH. Conversely, all patients with ERBB2 amplification were HER2 + by IHC. In the second-line and beyond, trastuzumab plus pertuzumab had the longest median time to treatment discontinuation (7.9 months), followed by trastuzumab deruxtecan (5.0 months). Among 25 patients who received ≥ 2 anti-HER2 agents, 24% had more durable clinical benefit to their second-line HER2 therapy compared to their first, as measured by the growth modulation index. Conclusions Multimodal HER2 testing is needed to accurately identify candidates for HER2-targeted treatment, as NGS alone misses a significant proportion of cases. Patients who develop resistance to one anti-HER2 agent may still achieve benefit from subsequent HER2-directed regimens. Early and serial treatment with HER2-directed agents should be considered for patients with HER2 + GI cancers.