Temporal trends in the incidence of second primary cancers in Northern Portugal: a population-based study.

The growing number of cancer survivors has led to an increase in the frequency of multiple primary cancers. This study aimed to describe the temporal trends in the incidence rates and standardized incidence ratios (SIRs) of second primary cancers (SPCs) among patients diagnosed with a first primary cancer (FPC) in 2000-03, 2004-07 and 2008-11 in Northern Portugal. Population-based samples of patients diagnosed with an FPC (excluding skin non-melanoma) in 3 periods of 4 years, between 1 January 2000 and 31 December 2011, and registered in the Portuguese North Region Cancer Registry were followed for the diagnosis of an SPC or death until 31 December 2013. Incidence rates and SIRs were estimated for each period by sex, and considering the time between FPC and SPC diagnosis (synchronous and metachronous). During follow-up, 10 119 (7.4%) SPCs were identified among patients diagnosed with an FPC in 2000-11 (n = 136 382). The incidence rate of SPCs was over 10-fold higher in the first few months, remaining stable over the follow-up. Higher rates were observed in 2004-07 and 2008-11. Overall, a greater proportion of SPCs was diagnosed among males than females. The proportion of SPCs diagnosed increased with age. Increases in SIRs of SPCs were observed from 2000-03 to 2008-11, ranging from 1.16 to 1.77 and from 1.54 to 2.33, among males and females, respectively. This was particularly evident for FPCs and SPCs of the lip, oral cavity, pharynx, oesophagus and larynx among males, and colon and rectum, lung, ovary and cervix among females. Survivors of cancer in Northern Portugal had higher incidence rates of cancer than the general population, which have increased over time. Our findings highlight the need for enhanced surveillance and tailored strategies for survivors of cancer, emphasizing the challenges of their heightened cancer risk, patient expectations, and associated economic burden.