Evaluation of the frequency of and survival from second primary cancers in North Portugal: a population-based study

A marked increase in cancer survival and in the frequency of second primary cancers (SPCs) has been observed in the latest decades, propelling the investigation of their burden at a population level. We aimed to quantify the proportion of SPCs among the incident cases in North Portugal and to describe their survival. We identified all SPCs (excluding skin nonmelanoma) registered by the North Region Cancer Registry (RORENO) from 2000 to 2003 according to the International Association of Cancer Registries and the International Agency for Research on Cancer guidelines. We classified tumors diagnosed more than 2 months after a first primary cancer (FPC) as metachronous. The observed survival was computed using vital status in December 2010. A total of 1607 SPCs (3.8% of all cancers) were registered (77.9% metachronous). The most frequent metachronous SPC topographies and the corresponding most frequent FPCs were of the colon (12.2%; FPC: prostate, breast, and stomach), lung (10.5%; FPC: bladder, stomach, and colon), and stomach (9.7%; FPC: prostate, breast, and bladder). The overall 5-year survival of individuals with metachronous SPCs was 47.4%; within the subgroups with higher (63.1%) and lower survival (31.1%), there were no significant differences across groups of FPCs with expectably different survival. The proportion of SPCs was that anticipated for a registry with approximately one decade of activity. The most common cancers in the general population were also frequent metachronous SPCs, whereas the most frequent FPCs were high incidence and survival cancers. The survival of metachronous SPCs did not vary with the survival expected for the FPCs.