This systematic review examines the reporting trends, prognostic implications, and treatment efficacy for chromosome 1q21 (+1q) gain and amplification in multiple myeloma (MM) randomized controlled trials (RCTs). The review searched Pubmed, Embase, and Cochrane Registry of RCTs from January 2012 to December 2022, focusing on MM RCTs. Among 124 included RCTs, 29 (23%) reported on +1q, with 10% defining thresholds for +1q. 14% reported survival data separately for gain and amplification, and 79% considered +1q a high-risk cytogenetic abnormality. Treatments such as lenalidomide maintenance, selinexor, and isatuximab improved progression-free survival (PFS) in patients with +1q. However, some RCTs showed no improvement in PFS for +1q patients. All interventions that improved PFS in RCTs also demonstrated benefit in the +1q subgroup. The review highlights significant heterogeneity in +1q reporting and calls for standardized reporting to better understand its prognostic implications.This systematic review examines the reporting trends, prognostic implications, and treatment efficacy for chromosome 1q21 (+1q) gain and amplification in multiple myeloma (MM) randomized controlled trials (RCTs). The review searched Pubmed, Embase, and Cochrane Registry of RCTs from January 2012 to December 2022, focusing on MM RCTs. Among 124 included RCTs, 29 (23%) reported on +1q, with 10% defining thresholds for +1q. 14% reported survival data separately for gain and amplification, and 79% considered +1q a high-risk cytogenetic abnormality. Treatments such as lenalidomide maintenance, selinexor, and isatuximab improved progression-free survival (PFS) in patients with +1q. However, some RCTs showed no improvement in PFS for +1q patients. All interventions that improved PFS in RCTs also demonstrated benefit in the +1q subgroup. The review highlights significant heterogeneity in +1q reporting and calls for standardized reporting to better understand its prognostic implications.