Highlight
The randomized phase III TrilynX trial evaluated xevinapant, an inhibitor of apoptosis proteins (IAP) inhibitor, added to standard platinum-based chemoradiotherapy (CRT) in patients with unresected locally advanced squamous cell carcinoma of the head and neck (LA SCCHN). Contrary to expectations, xevinapant plus CRT resulted in shorter event-free survival (EFS) and worse overall survival (OS) compared to placebo plus CRT. In addition, the xevinapant arm experienced higher rates of grade ≥3 treatment-emergent adverse events (TEAEs), serious adverse events, and deaths related to treatment. These findings highlight a negative benefit-risk profile of xevinapant in this clinical context.
Study Background and Disease Burden
Locally advanced squamous cell carcinoma of the head and neck (LA SCCHN), encompassing malignancies of the oropharynx (p16-negative only), hypopharynx, and larynx, remains a significant clinical challenge due to poor long-term outcomes despite aggressive treatment. Standard of care for unresectable disease often involves platinum-based chemoradiotherapy using cisplatin and intensity-modulated radiotherapy (IMRT), which can achieve cure in some but is often limited by suboptimal efficacy and significant toxicity.
Inhibitor of apoptosis proteins (IAPs) have emerged as therapeutic targets because their overexpression can confer treatment resistance by blocking programmed cell death, allowing cancer cells to survive chemotherapy and radiation. Xevinapant is a small-molecule IAP inhibitor developed to restore apoptosis and enhance therapy effects. Early phase studies suggested potential efficacy when combined with CRT, prompting evaluation in the TrilynX phase III trial to improve event-free survival in this patient population.
Study Design
The TrilynX study was a randomized, double-blind, placebo-controlled, phase III trial conducted between September 2020 and February 2023. It enrolled 730 patients with unresected LA SCCHN involving the oropharynx (p16-negative), hypopharynx, or larynx. Participants were randomized 1:1 to receive either oral xevinapant 200 mg daily or matched placebo, administered once daily on days 1–14 in each 21-day cycle, for a total of six cycles. Concurrently, all patients received standard chemoradiotherapy during the first three cycles, consisting of cisplatin 100 mg/m2 given once on day 2 of each cycle and intensity-modulated radiotherapy delivering a total dose of 70 Gy over 35 fractions.
The primary endpoint was event-free survival (EFS), evaluated by a blinded independent review committee. Secondary endpoints included progression-free survival (PFS), overall survival (OS), and treatment safety.
Key Findings
The trial randomized 364 patients to xevinapant plus CRT and 366 patients to placebo plus CRT. Median EFS was 19.4 months (95% CI, 14.5 to NE) in the xevinapant group versus 33.1 months (95% CI, 21.0 to NE) in the placebo group. The hazard ratio for EFS was 1.33 (95% CI, 1.05 to 1.67), indicating a statistically significant detriment with xevinapant; the p-value was reported as 0.9919, reflecting no benefit (noting possible typographical discrepancy, but directionally negative). Overall survival was also worse in the xevinapant arm, with a hazard ratio of 1.39 (95% CI, 1.04 to 1.86).
Safety analyses revealed a higher incidence of grade 3 or greater treatment-emergent adverse events in the xevinapant arm (87.9%) compared to placebo (80.3%). The most common severe adverse events in the xevinapant group included anemia (21.4%) and neutropenia (19.5%), comparable to placebo for neutropenia but higher for anemia. Serious adverse events occurred in 53.3% of patients receiving xevinapant versus 36.2% in the placebo group. Treatment-emergent adverse events leading to death were reported in 6.0% of patients treated with xevinapant compared to 3.7% in the placebo arm.
Overall, these results robustly demonstrated that adding xevinapant to platinum-based CRT not only failed to improve cancer control outcomes but was associated with increased toxicity and worse survival.
Expert Commentary
The TrilynX study provides critical insight into the role of IAP inhibition in LA SCCHN. Despite strong biological rationale, the clinical outcomes with xevinapant were unfavorable. This highlights the complexity of apoptotic pathways and potential unintended effects of IAP inhibitors in the context of definitive chemoradiotherapy. The unexpected worse survival and toxicity signals raise concerns about off-target effects or interference with cisplatin and radiotherapy efficacy.
The results contrast with earlier phase II studies that showed promise, underscoring the importance of confirmatory phase III trials. These findings reinforce the need for careful translational research to clarify mechanisms underlying adverse outcomes and for biomarkers predicting which patients might benefit or be harmed.
Limitations of the trial include lack of biomarker stratification for IAP expression levels and exclusion of p16-positive oropharyngeal cancer, which may behave differently. The generalizability is robust for unresectable LA SCCHN but may not apply to other head and neck subtypes or HPV-positive disease.
Conclusion
The TrilynX randomized phase III trial demonstrated that the addition of xevinapant to standard platinum-based chemoradiotherapy in unresected locally advanced squamous cell carcinoma of the head and neck did not improve event-free survival and was associated with worse overall survival and increased severe toxicities. These results do not support the use of xevinapant in this setting and highlight the challenges in targeting apoptotic pathways to enhance chemoradiotherapy efficacy.
Future investigations should focus on deepening mechanistic understanding, identifying predictive biomarkers, and exploring alternative therapeutic strategies to improve outcomes for patients with unresected LA SCCHN.
References
1. Bourhis J, Licitra LF, Burtness B, et al. Xevinapant or Placebo Plus Platinum-Based Chemoradiotherapy in Unresected Locally Advanced Squamous Cell Carcinoma of the Head and Neck (TrilynX): A Randomized, Phase III Study. J Clin Oncol. 2025 Sep 3:JCO2500272. doi: 10.1200/JCO-25-00272. Epub ahead of print. PMID: 40902136.
2. Cohen EEW, et al. Current Standards and Emerging Treatments in Head and Neck Squamous Cell Carcinoma. Lancet Oncol. 2021;22(7):e287-e297.
3. Fulda S. Targeting Inhibitor of Apoptosis Proteins for Cancer Therapy. Adv Exp Med Biol. 2020;1240:117-136.
4. Haddad R, et al. Advances in Chemoradiotherapy for Locally Advanced Head and Neck Cancer. Nat Rev Clin Oncol. 2020;17(12):694-708.
