Background: Cancer survivors are at risk of developing second and subsequent cancers, referred to as multiple primary cancers (MPCs). The number of patients with multiple primaries is growing, with up to 10% of cancer survivors developing a second primary within 30 years. It is not clear whether the risk of MPCs has increased over recent decades but advances in early detection, radiological imaging, and potentially harmful effects of certain cancer treatments raise this possibility. A systematic review was undertaken to assess whether there has been a temporal change in the risk of developing MPCs.
Methods: A systematic search to identify population-based studies of MPCs was performed in Medline/PubMed and Embase databases from inception to March 2015. Included studies were those reporting risk of MPCs at any site in patients following a first cancer at any site or a specific site, using standard incidence ratios (SIRs) or equivalent, and with analysis stratified by calendar years.
Results: 17 of 1193 articles were eligible to be included in this review, comprising 16 population-based studies and 1 monograph. MPC incidence was reported in more than 3.5 million cancer survivors. A higher rate of MPCs following a first cancer with all sites combined was reported in more recent than earlier calendar periods in all three relevant studies, with SIRs ranging from 1.14 in the early 1980s to 1.21-1.46 in the late 1990s. The remaining 14 studies reported various temporal trends in the risk of developing MPCs after a first cancer of specific site, but most showed little change.
Conclusion: Overall, the risk of developing MPCs appears to have increased over time when considering studies of all primary cancer sites combined. The current literature is insufficient to explain the reason behind this change, and more long-term surveillance is needed to confirm and understand this pattern.