INCIDENCE OF 2ND PRIMARY CANCERS IN OSAKA RESIDENTS, JAPAN, WITH SPECIAL REFERENCE TO CUMULATIVE AND RELATIVE RISKS

This study was conducted to examine the incidence rates and cumulative risks of second primary cancers in Osaka and to compare the observed number of second primary cancers with the expected number calculated u sing cancer incidence rates among Osaka residents. Study subjects were all reported cases aged 0-79 who were first diagnosed as having a fir st primary cancer between 1966-86. Incidence of second primary cancer among the study subjects was examined through to the end of 1989. The total number of study subjects was 217,307. During the follow-up perio d (mean duration: 3.7 years), second primary cancers developed in 5,07 1 patients (2.3%). Incidence of synchronous (interval <3 months) and m etachronous (interval greater than or equal to 3 months) second primar y cancers increased in the later years. Incidence rates of second prim ary cancers were significantly associated with gender (male), age and calendar year at diagnosis of the first cancer. Based on the incidence rates, cumulative risk of developing metachronous second primary canc er was calculated. The ten-year cumulative risk was estimated as 10% f or those who developed their first cancer during their sixties in 1978 -83. The observed number of second primary cancers (including synchron ous) was compared with the expected number. The ratios of observed-to- expected numbers were generally lower than 1.0 among those who develop ed their first cancer in 1966-77, while these ratios were higher than 1.0 among those who developed their first cancer in 1978-86. The ratio s were much higher than 1.0 among those who developed their first canc er in their childhood and youth. Patients who had developed cancer of the colon, larynx, lung, bladder, or breast (female) showed significan tly higher risk of developing second primary cancer during the period 1-4 years after diagnosis of the first cancer.