The study, published in Cancer Immunology, Immunotherapy, evaluated sintilimab, a monoclonal antibody that blocks the programmed cell death protein 1, or PD-1, a molecular brake that tumors exploit to disable attacking immune cells. By releasing this brake, PD-1 inhibitors allow T cells to recognize and destroy cancer cells that would otherwise hide in plain sight. Sintilimab has already transformed the treatment landscape for several cancers in China, but its role in the post-surgical setting for esophageal cancer had remained largely uncharted territory.

The clinical problem the researchers tackled is a genuine one. While neoadjuvant therapy followed by esophagectomy has become a standard approach for locally advanced esophageal squamous cell carcinoma, many patients still harbor residual pathological disease after treatment, and others undergo upfront surgery only to be found with high-risk features such as deep tumor invasion or lymph node involvement. For these patients, evidence to guide adjuvant immunotherapy has been sparse. Most of the landmark immunotherapy trials in esophageal cancer focused on advanced, metastatic disease or on the neoadjuvant window before surgery, leaving the post-operative period as a therapeutic blind spot.

The trial, registered as ChiCTR2100049784, enrolled 32 patients between August 2021 and July 2023 at a single center. All had undergone R0 resection, meaning surgeons had removed the tumor with microscopically clear margins, the best achievable surgical outcome. Yet every patient carried high-risk pathology: either ypT1-4a and/or ypN+ disease after neoadjuvant therapy, or pT3-4 and/or pN+ disease after surgery performed first without pre-treatment. The majority, 27 patients or 84.4 percent, had received neoadjuvant therapy combining a PD-1 inhibitor with chemotherapy before their operation. Two patients, 6.3 percent, had neoadjuvant chemotherapy alone, and three patients, 9.4 percent, had undergone upfront surgery.

The treatment regimen was straightforward but demanding. Patients received sintilimab monotherapy every three weeks for up to 12 months, corresponding to 17 planned cycles. No chemotherapy or radiation was layered on top; the immunotherapy stood alone. The primary endpoint was the one-year recurrence-free survival rate, a prespecified benchmark the study needed to meet to be considered a success. Secondary endpoints included overall survival and safety, assessed throughout the treatment period and beyond.

The results exceeded expectations for a trial of this size. At a median follow-up of 47.0 months, nearly four years, the median recurrence-free survival had not been reached, meaning more than half of the patients had not experienced a recurrence by the time of analysis. The one-year recurrence-free survival rate stood at 87.5 percent, comfortably meeting the prespecified primary endpoint, while the two-year rate was 65.6 percent. Overall survival followed a similarly favorable trajectory: 93.8 percent of patients were alive at one year and 78.1 percent at two years, with median overall survival likewise not reached.

Safety data provided reassurance that the approach is tolerable. Treatment-related adverse events occurred in 13 patients, or 40.6 percent of the cohort, and grade 3 or higher events, the serious toxicities that can threaten organ function or require hospitalization, appeared in 7 patients, or 21.9 percent. Critically, no treatment-related deaths occurred, a notable finding given that immune checkpoint inhibitors can occasionally trigger severe immune-mediated inflammation in organs such as the lungs, liver, colon, or endocrine glands. Despite the manageable safety profile, adherence to the full course was imperfect: 17 patients, or 53.1 percent, completed all 17 planned cycles, a completion rate that reflects the real-world challenges of maintaining a year-long treatment, whether due to adverse events, recurrence, or patient choice.

The immunological rationale underlying these findings deserves attention. Neoadjuvant chemoradiation or chemoimmunotherapy can prime the immune system by releasing tumor antigens as cancer cells die, creating a window of heightened immune surveillance. Administering a PD-1 inhibitor in the adjuvant setting may then consolidate that priming, helping circulating and tissue-resident T cells eliminate microscopic residual disease before it can establish clinically detectable metastases. The strong showing of the 87.5 percent one-year recurrence-free survival rate in a cohort overwhelmingly composed of patients treated with neoadjuvant PD-1 blockade plus chemotherapy suggests that the perioperative sequencing of immunotherapy, before and after surgery, may act synergistically, though the single-arm design cannot formally disentangle the contributions of each component.

The authors and independent observers alike caution that the study’s design imposes limits on interpretation. With no control arm, it is impossible to say with certainty how patients would have fared with observation alone or with alternative adjuvant strategies, and the single-center enrollment of 32 patients means the confidence intervals around the survival estimates are wide. Selection factors, including the general fitness required to undergo esophagectomy and then a year of immunotherapy, may also inflate outcomes relative to the broader population of high-risk patients. The researchers themselves state that the findings support further evaluation in larger randomized controlled trials with longer follow-up, and the field is watching ongoing perioperative immunotherapy studies in esophageal cancer that may soon provide the randomized evidence needed to change guidelines.

Even with those caveats, the trial adds an important piece to a rapidly evolving puzzle. Esophageal squamous cell carcinoma remains one of the most lethal malignancies worldwide, with five-year survival historically languishing in the double digits even after curative-intent surgery. The demonstration that adjuvant sintilimab monotherapy met its prespecified efficacy endpoint with manageable toxicity and no treatment-related deaths provides a template for how post-operative immunotherapy could be integrated into multimodal treatment programs. If larger randomized trials confirm these results, the standard of care for high-risk resected esophageal cancer could shift from watchful waiting after surgery to a full perioperative immunotherapy strategy, turning a period of anxious uncertainty into an active, immune-based defense against recurrence.

Subject of Research: Adjuvant PD-1 inhibitor therapy for high-risk resected esophageal squamous cell carcinoma

Article Title: Efficacy and safety of adjuvant sintilimab monotherapy in high-risk resected esophageal squamous cell carcinoma: a prospective, single-arm phase II trial

Article References: Efficacy and safety of adjuvant sintilimab monotherapy in high-risk resected esophageal squamous cell carcinoma: a prospective, single-arm phase II trial. (n.d.). https://doi.org/10.1007/s00262-026-04579-6

Image Credits: AI Generated

DOI: 10.1007/s00262-026-04579-6

Keywords: esophageal squamous cell carcinoma, sintilimab, PD-1 inhibitor, adjuvant immunotherapy, recurrence-free survival, phase II trial, esophagectomy, cancer immunotherapy, neoadjuvant therapy, overall survival, treatment-related adverse events, Peking University Cancer Hospital