Incidence of second primary cancers in North Portugal-a population-based study

Longitudinal studies are needed to characterise the burden of second primary malignancies among cancer survivors. Therefore, we quantified the incidence rate and cumulative incidence of second primary cancers (SPC) and standardised incidence ratios (SIR) in a population-based cohort of subjects diagnosed with a first primary cancer (FPC).

We evaluated a cohort of cancer patients from the Portuguese North Region Cancer Registry (RORENO), with the first diagnosis in 2000-2003 (n = 39451), to estimate the incidence rate and cumulative incidence of SPC and standardised incidence ratios (SIR), for different periods of follow-up, up to 5 years; SPC were defined according to the International Association of Cancer Registries and the International Agency for Research on Cancer guidelines.

The incidence rate of SPC was more than 5-fold higher in the first 2 months of follow-up than in the period between 2 months and 5 years (metachronous SPC), across which the incidence rates were relatively stable. Cancer survivors had an overall higher incidence rate of cancer than the general population (SIR = 1.31 (95 % confidence interval (CI), 1.25-1.38)), although that difference faded when only metachronous SPC were considered (SIR = 1.02 (95 % CI, 0.96-1.08)). Cancer incidence rates were higher among female lung FPC survivors and lower in prostate FPC cancer survivors than in the general population. The 5-year cumulative risk of developing a metachronous SPC was 3.0 % and reached nearly 5.0 % among patients with FPC associated with lower risk of death.

Cancer survivors had higher incident rates of cancer that the general population, especially due to diagnoses in the first months following the FPC. Nevertheless, after this period SPC remain frequent events among cancer survivors.

SPC constitute an important dimension of the burden of cancer survivorship, and this needs to be taken into account when defining strategies for surveillance, prevention and counselling.