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ResearchPUBMEDWednesday, April 1, 2026 · April 1, 2026

Baseline tumor burden and outcomes in patients with rare cancers treated with immunotherapy (Southwest Oncology Group trial S1609).

WHY IT MATTERS

If baseline tumor size predicts treatment response in rare cancers, doctors could better counsel patients on expected outcomes and identify which patients might benefit most from this dual immunotherapy approach before starting treatment.

Researchers studied whether the amount of cancer in a patient's body before treatment affects how well two immunotherapy drugs work together. They looked at 722 patients with rare cancers who received nivolumab and ipilimumab (two drugs that help the immune system fight cancer). The study wanted to understand if patients with smaller tumors do better than those with larger tumors when treated with these combination drugs.

Baseline tumor burden and outcomes in patients with rare cancers treated with immunotherapy (Southwest Oncology Group trial S1609). Abstract: It has been suggested that baseline tumor burden may correlate with immune checkpoint inhibitor (ICI) outcome for individual tumor types in which ICIs are standardly used. The authors investigated whether pretreatment tumor burden correlates with overall survival (OS), progression-free survival (PFS), and tumor regression among patients who had rare cancers treated with dual ICIs. Southwest Oncology Group study S1609 was a phase 2, National Cancer Institute/Southwest Oncology Group basket study (>1000 sites) evaluating nivolumab plus ipilimumab in 53 cohorts of patients who had rare/ultrarare malignancies (ClinicalTrials.gov identifier NCT02834013). Overall, 722 patients were included in this secondary analysis, all of whom had measurable disease (Response Evaluation Criteria in Solid T Authors: Swiecicki et al. Journal: Cancer MeSH: Humans, Male, Female, Neoplasms, Middle Aged, Tumor Burden, Aged, Nivolumab, Adult, Ipilimumab

ASK YOUR DOCTOR

If you have a rare cancer and your doctor is considering immunotherapy, ask whether your baseline tumor burden (the amount of cancer visible before treatment) affects the expected effectiveness of treatment.

Find a specialist →Learn more ↗
immunotherapyrare cancertumor burdenclinical trialcheckpoint inhibitors

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