Incidence of multiple primary malignancies in women diagnosed with breast cancer

Using data from the Umbrian Population Cancer Registry (RTUP) we tested the hypothesis of relationships between several subsequent cancer sites in women who had had breast cancer. New patients (7,840) were collected from the RTUP between 01/01/1994 and 31/12/2006; 24 DCO cases were excluded; 332 successive multiple cancers in 320 patients were recorded. Including all second cancers, metachronous contralateral breast cancer, the observed/expected ratio (SIR) was non-significant. Excluding these cases, SIR was significantly lower whether with or without second skin carcinomas. SIR of all second metachronous contralateral cancers, excluding skin carcinomas, was non-significant. Significantly lower risk involved the colorectum, stomach, pancreas and metachronous breast with different histology. A significant excess was found of melanoma and total second breast cancers, including the contralateral. The excessive skin melanoma in breast cancer survivors was attributed to the relationship with BRCA2 and CDKN2A mutation-positive patients. The excess risk due to the CDKN2A mutation should also include pancreatic cancer which, in the present study, presented a significantly lower risk.