Incidence of multiple primary cancers and interval between first and second primary cancers.
Bottom Line: A second primary cancer developed in 14 167 of 174 477 subjects (8.1%) during a median follow-up of 1.8 years.Some specific relationships were observed between sites with risk factors in common, such as smoking, drinking, and hormone status.The SIRs were relatively high after approximately 10 years for all sites, and trends differ among cancer sites.
Affiliation: Department of Mathematical Health Science, Graduate School of Medicine, Osaka University, Osaka, Japan.Show MeSH
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Mentions: A previous study reported a significant risk peak for second cancers between the eighth and ninth year after diagnosis of breast cancer; the authors considered this was probably attributable to a late effect of local radiotherapy for the first breast cancer.(29) In the present study, the SIRs for first breast cancers were relatively high after approximately 10 years; however, this increase was not statistically significant (P < 0.05). We observed similar increases for larynx, uterus, and blood cancers. The proportions of subjects in the present study with these cancers who had received radiotherapy were relatively high except for blood cancers; namely, 6.2% for all sites, 54.3% for larynx, 17.8% for uterus, 11.8% for breast, and 6.1% for blood. To confirm a late effect of radiotherapy, we carried out a stratified analysis by treatment history of radiotherapy. The Nagasaki Prefecture Cancer Registry collects information on the first course of treatment. Subjects were classified according to whether or not they had received radiotherapy as part of their initial cancer treatment. Figure 3 shows the trends in SIRs after diagnosis of first primary cancers of all sites and these sites. The SIRs of patients treated without radiotherapy were consistently around 1.00 except for the first year, whereas those of patients treated with radiotherapy increased after the second year and were relatively high in approximately 7 and 12 years. Therefore, a late effect of radiotherapy could partly explain the increased risk. The SIRs according to cancer sites were not stable due to the small number of patients, and the clear differences between the SIRs of patients treated with radiotherapy and those of patients treated without radiotherapy were not observed. Our results, however, implied that follow-up for at least 10 years after diagnosis of the first primary cancer is needed for patients with these cancers, especially those who have received radiotherapy. We have to consider radiation dose, age at exposure to radiation, and subsequent treatment to clarify the effect of radiotherapy.
Affiliation: Department of Mathematical Health Science, Graduate School of Medicine, Osaka University, Osaka, Japan.