Long term outcomes of the Indian childhood cancer survivorship (C2S) cohort: a multicentre study (2016–2024)

Background Almost 90% of childhood cancers occur in lower income- and middle-income countries (LMICs) like India, leading to a growing population of cancer survivors. However, data on long-term outcomes and late effects are limited. The Indian Childhood Cancer Survivorship (C2S) Study was envisaged to build a nationwide survivor cohort and systematically capture treatment exposures and long-term outcomes. Methods The C2S study is a prospective multicentric observational cohort initiated in 2016 under the Indian Pediatric Hematology Oncology Group (InPOG-LE-16-01). Children diagnosed with cancer before 18 years of age and in remission post-treatment were enrolled. Demographic, clinical, and treatment exposure data were collected at respective centres and monitored centrally. Follow-up was conducted every three months, assessing survival, relapse, and abandonment rates. Findings As of December 2024, the study includes data from 20 centres across India with 5419 survivors being enrolled, with survival data available for 5140. Acute leukemia was the most common diagnosis (40.9%). Common therapeutic exposures included chemotherapy (94.7%), surgery (30.3%), and radiotherapy (26.3%). The 5-year overall survival (OS) and event-free survival (EFS) rates for the entire cohort were 94.5% (95% CI: 93.7–95.3)% and 89.9% (95% CI: 88.8–91.0)%, respectively. For the 2266 survivors with ≥2 years post-treatment follow-up, 5 y-OS and EFS were 98.2 (95% CI: 97.5–98.7)% and 95.7 (95% CI: 94.7–96.6)%, respectively. Interpretation The C2S study represents the first structured attempt to build a nationwide childhood cancer survivors’ cohort in India. This cohort will serve as a denominator for future research on late effects, support the development of survivorship guidelines, and inform policy planning in India and comparable LMIC settings. Funding There was no dedicated funding for this study.