Second Primary Cancers Following Cancer Among Adolescents and Young Adults in Queensland, Australia, 1982-2018.

Purpose: Increased risk of second primary cancers is an unwanted consequence of cancer survivorship. While the epidemiology of second cancers is well-documented for children and older people, less is known about second cancers among adolescent and young adult (AYA) cancer survivors. Methods: Unit record data were obtained from the Queensland Cancer Register. The study cohort comprised Queensland residents aged 15 to 39 years who were diagnosed with a first primary invasive cancer between 1982 and 2013. Follow-up on second cancers was available for a minimum of 5 years to the end of 2018. Standardized incidence ratios (SIRs) were used to approximate the risk of a second primary cancer relative to the general population. Results: In total, 3086 second primary cancers were observed among 34,431 eligible AYA patients (9%), equating to an overall SIR of 1.59 (95% confidence interval [CI] 1.53-1.64). Melanoma ( n  = 853, 28%) and female breast cancer ( n  = 594, 19%) were the most common types of second primary cancer in the study cohort. Relative risk of all second primary cancers combined among AYA patients was inversely associated with age and was highest within the period immediately after first diagnosis irrespective of age group; for example, patients aged 15-24 at first diagnosis recorded more than four times as many second primary cancers than expected within 2 years of their first cancer (SIR = 4.40, 95% CI 2.83-6.82). Conclusions: Detailed data on second primary cancers among AYA cancer survivors are important in promoting increased awareness and to inform the development of targeted prevention and surveillance strategies.