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.