S13 Ep26: ASCO 2025 Plenary — MATTERHORN

Two Onc Docs, hosted by Samantha A. Armstrong, MD, and Karine Tawagi, MD, is a podcast dedicated to providing current and future oncologists and hematologists with the knowledge they need to ace their boards and deliver quality patient care. Dr Armstrong is a hematologist/oncologist and assistant professor of clinical medicine at Indiana University Health in Indianapolis. Dr Tawagi is a hematologist/oncologist and assistant professor of clinical medicine at the University of Illinois in Chicago.

In this episode, OncLive On Air® partnered with Two Onc Docs to bring a discussion of key data from the phase 3 MATTERHORN trial (NCT04592913), which were presented at the 2025 ASCO Annual Meeting. MATTERHORN was a randomized, double-blind, multinational study evaluating the addition of durvalumab (Imfinzi) to FLOT (5-fluorouracil, leucovorin, oxaliplatin, and docetaxel) in patients with previously untreated, resectable gastric or gastroesophageal junction adenocarcinoma.

In the MATTERHORN trial, 948 patients were randomly assigned 1:1 to receive either durvalumab or placebo in combination with perioperative FLOT, followed by 10 cycles of durvalumab or placebo as adjuvant therapy. The primary end point was event-free survival (EFS); secondary end points included overall survival (OS) and pathological complete response (pCR).

The trial met its primary end point. Durvalumab plus FLOT (n = 474) significantly improved EFS vs placebo plus FLOT (n = 474; HR, 0.71; 95% CI, 0.58-0.86; P < .001), representing a 29% reduction in risk of progression, recurrence, or death. The interim OS analysis showed a nonsignificant trend favoring durvalumab (HR, 0.78; 95% CI, 0.62-0.97; P = .025). The pCR rate was 19% (95% CI, 15.75%-23.04%) with durvalumab vs 7.2% (95% CI, 5.02%-9.88%) with placebo.

Toxicity profiles were comparable between the 2 groups, though immune-related adverse effects were more frequent with durvalumab. Importantly, the addition of durvalumab did not delay surgery or initiation of adjuvant therapy.

Although the MATTERHORN regimen is not yet FDA approved or included in the National Comprehensive Cancer Network guidelines, this trial demonstrates a promising EFS benefit and potential practice-changing implications, pending mature OS data and further molecular subgroup analyses, according to Armstrong and Tawagi.