Childhood and adult cancers: contrasts and commonalities.

Tumours occurring in children differ considerably from those occurring at older ages but exhibit common features. Those occurring in the teenage/young adult (TYA) years represent a transitional mixture of child and adult tumours and pose a considerable challenge for optimal clinical management and service provision. Nevertheless the fundamental processes of malignant change, arising from genetic/epigenetic interaction with environmental exposures, seem to operate across all ages and the entire tumour spectrum. We focus here on the ways in which genotype (and epigenetic modification), growth processes (particularly in utero), and exposure to ionising radiation (in conjunction with genetic susceptibility) affect cancer risk from childhood to adulthood, whether as a primary occurrence, or a second primary tumour following earlier primary occurrence and treatment.