1. Structurally, the TOPAZ-1 trial strictly caps chemotherapy at 8 cycles, transitioning patients to durvalumab monotherapy. In contrast, KEYNOTE-966 discontinues cisplatin at 8 cycles but permits continuous, indefinite gemcitabine maintenance alongside pembrolizumab. Despite this structural difference, the survival curves of both trials yield remarkably similar median overall survival — 12.8 months for TOPAZ-1 and 12.7 months for KEYNOTE-966 — and both feature a plateauing tail that highlights a durable immunotherapy benefit. Continuing maintenance gemcitabine does not appear to significantly alter survival compared to single-agent immunotherapy maintenance, though it adds potential hematologic toxitoxicity.
2. Navigating this clinical choice for a self-funding family in Nigeria requires a delicate balance between survival benefits and severe financial toxicity. I would frame the discussion around fixed-duration versus indefinite commitments. Fixed-duration durvalumab (TOPAZ-1) offers a defined financial horizon where the patient receives 8 cycles of combination chemoimmunotherapy, followed by durvalumab monotherapy up to a set timeline. Indefinite pembrolizumab (KEYNOTE-966) introduces a prolonged financial burden that risks treatment interruption due to unexpected bankruptcy. Given the local socioeconomic realities, I would recommend a fixed-duration approach like durvalumab, which allows the family to budget accurately and minimize the risk of forced early cessation.
If out-of-pocket funds become completely exhausted during maintenance immunotherapy, I would use pragmatic dose-modification strategies and revised surveillance to protect his existing response. I could extend the dosing intervals of the checkpoint inhibitor (e.g., using extended double-dose intervals) to reduce overall drug administration costs. Alternatively, if immunotherapy must be stopped entirely, I would transition him to surveillance-only maintenance. I would space out CT scans while utilizing cost-effective baseline biomarker monitoring, such as tracking serial serum CA 19-9 levels and routine liver function tests, to detect early disease progression without imposing excessive financial stress on the family.
References
Oh DY, et al. Durvalumab plus gemcitabine and cisplatin in advanced biliary tract cancer. NEJM Evid. 2022;1(8).
Kelley RK, et al. Pembrolizumab plus gemcitabine and cisplatin for advanced biliary tract cancer (KEYNOTE-966): a randomised, double-blind, placebo-controlled, phase 3 trial. Lancet. 2023;401(10391):1853-1865.
FDA Approval Summary: Durvalumab and Pembrolizumab, Immune Checkpoint Inhibitors for Unresectable or Metastatic Biliary Tract Cancers. PMC Journal. 2024.