Second primary cancers in breast cancer patients in Slovenia

Data from the Cancer Registry of Slovenia were used in a cohort studyto determine whether the incidence of second primary cancers in patients withfirst primary breast cancer differs from the incidence expected in thegeneral population. Special interest was given to long-term survivors. Theexpected numbers of second primary cancers were calculated by multiplying thenumber of appropriate person-years at risk by the corresponding age-andcalendar-period-specific cancer incidence rates for women in Slovenia. Therisk of a second primary cancer was expressed as the standardized incidenceratio (SIR). Of the 8,917 patients newly diagnosed in the period 1961-85 andfollowed-up to the end of 1994, 547 (6.2 percent) developed second primarycancers, whereas 410 (4.7 percent) were expected (SIR = 1.3, 95 percentconfidence interval [CI] = 1.2-1.4). The risk was higher among youngerpatients. In long-term survivors, the risk was increased significantly forsecond primary cancer of th e breast (SIR = 1.4, CI = 1.1-1.7), lung cancer(SIR = 1.6, CI = 1.1-2.3), melanoma (SIR = 2.7, CI = 1.5-4.4) andnon-melanoma skin cancers (SIR = 2.0, CI = 1.6-2.4), corpus uteri cancer (SIR= 1.6, CI = 1.2-2.1), ovarian cancer (SIR = 2.3, CI = 1.7-3.0), and thyroidcancer (SIR = 2.5, CI = 1.2-4.6). Our results confirm the findings of severalcohort studies carried out in Europe, the United States, and Japan,indicating that breast cancer patients should be monitored carefully for theoccurrence of second primary cancers.