Population-Based Survival of Childhood and Adolescent Cancers (0–19 Years) in Madrid: Analysis by Sex, Age, Tumour Type, and Stage

<b>Background/Objectives:</b> In Europe, over 80% of children diagnosed with cancer survive at least 5 years. To improve cancer monitoring, the Paediatric Population-Based Cancer Registry (PCRM) was established in the Community of Madrid. This study aimed to describe population-based 1-, 3- and 5-year survival for children and adolescents diagnosed with cancer, by sex, age, tumour type and stage at diagnosis. <b>Methods:</b> Data were extracted from the PCRM, which reviews all cases identified through integrated primary care, hospital discharge, and mortality data, using electronic medical records. Patients aged 0-19 diagnosed with primary malignant cancer between 2015 and 2018 were included, with follow-up for vital status through October 2024. Stage was classified using the 2014 Toronto Childhood Cancer Staging Guidelines (tier 2). Kaplan-Meier methods were used to estimate survival, and log-rank tests assessed group differences. Cox regression was used to quantify the effect of localized vs. advanced disease. <b>Results:</b> The analysis included 862 patients. Most frequent cancers were leukaemia (24.1%), lymphomas (22.2%) and central nervous system (CNS) tumours (12.6%). Stage was assigned to 88.4% tumours. Overall survival was 93.6% in 1 year and 85.9% in 5 years. Five-year survival was 83.7% for leukaemia, 97.4% for lymphomas, 66.1% for CNS tumours; 85.8% in boys vs. 85.9% in girls (<i>p</i> = 0.908); 85.2% in children aged 0-14 years vs. 87.8% in adolescents aged 15-19 years (<i>p</i> = 0.314); and 69.9% for advanced vs. 89.7% for early-stage (<i>p</i> < 0.001), with a 3.3-fold higher mortality risk. <b>Conclusions:</b> This population-based study offers promising survival estimates reaching 86% globally at 5 years while revealing differences by cancer type and stage. It also highlights the Toronto Guidelines as a valuable tool for standardizing cancer registry methods and providing useful epidemiological indicators.