BACKGROUND: Treatment abandonment (TxA) is a primary cause of therapy failure in children with cancer in low-/middle-income countries. We explored the absence of social support network (SSN), among other predictive factors, and TxA in children with cancer in Cali, Colombia. PROCEDURE: In this prospective cohort study, we included children diagnosed with cancer at a public university hospital. A social worker and a psychologist administered semistructured questionnaires to patients’ caregivers. We extracted information from the questionnaires about social, economic, and psychological conditions of the patients’ families. Outcomes were death, relapse, and TxA. Failure either to start or to continue the planned course of curative treatment for 4 weeks or more was defined as TxA. We identified events with Cali’s childhood cancer outcomes surveillance system (VIGICANCER). We adjusted the hazard ratios (HRs) for potential confounders using multivariate Cox regression analyses. RESULTS: Among 188 patients diagnosed from January 2011 to June 2013, 99 interviews were conducted. Median age was 5 years old (range: 0.3, 14.9), 53% were male, 17% were of Colombian-Indian ethnicity, and 68% lived in rural areas. The 2-year cumulative incidence of TxA was 21% (95% confidence interval [CI]: 13, 35) and the annual proportion was 14%. The adjusted HR for the absence of SSN was 4.9 (95% CI: 1.6, 15.3). CONCLUSIONS: We found a strong association between the absence of SSN and TxA that was independent of other covariates, including surrogate measures of wealth. Our findings highlight the imperative understanding of social ties and support surrounding children’s families for planning strategies to prevent TxA.