Abstract
Cancer in Adolescents and Young Adults (AYAs) represents a unique biological intersection, encompassing malignancies typical of both paediatric and older adults, as well as age-specific cancers. Yet, diagnostic and treatment approaches are not tailored to AYAs, potentially overlooking age-specific molecular characteristics. This review examines genomic differences between AYAs and paediatric and older patients, emphasising trends in cancer driver genes and identifying knowledge gaps that limit our understanding of AYA cancer biology. Across studies and cancer types, the AYA age range varies but is typically defined as 15-39 years. Remarkably, for nearly half of cancers diagnosed in AYAs, little or no literature exists on genomic differences or similarities compared to other age groups. Common cancers like testicular cancer and gynaecological cancer are underrepresented, while other typical AYA cancers such as thyroid cancer entirely lack comparative literature. In contrast, less common AYA cancers such as lung cancer and colorectal cancer are investigated extensively. Although genomic differences are reported across cancer types and in pan-cancer analyses, findings are often not generalisable to relevant subtypes or inconsistent, and insights gained are limited by the use of single-gene assays or small gene panels. This review reveals an imbalance between the global incidence of AYA cancers and the scope of comparative genomic studies, as well as a lack of broader comprehensive molecular profiling. Addressing these gaps through broader genomic research, particularly in underexplored cancers, is essential to determine whether AYA tumour biology is indeed distinctive, and how age-appropriate, genomics-driven precision oncology should be delivered.