Colorectal Carcinoma in Childhood and Adolescence: Microsatellite Instability Correlates With a Favorable Prognosis

ABSTRACT Background Colorectal cancer (CRC) accounts for 10% of cancer cases worldwide; however, pediatric CRC is extremely rare, with an annual incidence of one to two cases per million. Microsatellite instability (MSI) has been shown to play a relevant prognostic role in adult CRC. Corresponding data for pediatric CRC are lacking. This study examines MSI in pediatric CRC. Procedure Patient‐, tumor‐, and treatment‐related data of patients less than 18 years with CRC enrolled in the German Registry for Rare Pediatric Tumors (STEP) between 2005 and 2023 were analyzed and compared with data on patients less than 30 years with CRC and known MSI status from the Surveillance, Epidemiology, and End Results Program (SEER). Results Forty‐one patients with CRC were recorded in STEP. Cancer predisposition syndromes were identified in 52% of tested cases, especially in CRC with MSI (84.6%). The SEER cohort included 803 CRC patients under 30 years, 52 of whom were under 20 years. Most cases were at an advanced stage at diagnosis, with localized disease being rare (STEP: 4.9%, SEER: 16.4%). The 5‐year overall survival (OS) of STEP patients was 47.9% ± 9.7%. MSI was observed in 37.5% (STEP) and 32.7% (SEER <20 years) of patients. CRCs with MSI had lower rates of distant metastases and were associated with a significantly better survival (STEP 5‐year OS: MSI 85.1% ± 9.7% vs. no‐MSI 28.3% ± 11.2%, p = 0.007). Conclusions While pediatric CRCs overall more often demonstrate advanced stages, unfavorable histology, and a poorer prognosis than adult CRC, MSI is more common in pediatric CRC and is associated with superior survival.