CANCER INCIDENCE IN ATOMIC-BOMB SURVIVORS .2. SOLID TUMORS, 1958-1987

This report presents, for the first time, comprehensive data on the in cidence of solid cancer and risk estimates for A-bomb survivors in the extended Life Span Study (LSS-E85) cohort. Among 79,972 individuals, 8613 first primary solid cancers were diagnosed between 1958 and 1987. As part of the standard registration process of the Hiroshima and Nag asaki tumor registries, cancer cases occurring among members of the LS S-E85 cohort were identified using a computer linkage system supplemen ted by manual searches. Special efforts were made to ensure complete c ase ascertainment, data quality and data consistency in the two cities . For all sites combined, 75% of the cancers were verified histologica lly, 6% were diagnosed by direct observation, 8% were based on a clini cal diagnosis, and 12.6% were ascertained by death certificate only. A standard set of analyses was carried out for each of the organs and o rgan systems considered. Depending on the cancer site, Dosimetry Syste m 1986 (DS86) organ or kerma doses were used for computing risk estima tes. Analyses were based on a general excess relative risk model (the background rate times one plus the excess relative risk). Analyses car ried out for each site involved fitting the background model with no d ose effect, a linear dose-response model with no effect modifiers, a l inear-quadratic dose-response model with no effect modifiers, and a se ries of linear dose-response models that included each of the covariat es (sex, age at exposure, time since exposure, attained age and city) individually as effect modifiers. Because the tumor registries ascerta in cancers in the registry catchment areas only, an adjustment was mad e for the effects of migration. In agreement with prior LSS findings, a statistically significant excess risk for all solid cancers was demo nstrated [excess relative risk at 1 Sv (ERR(1 Sv)) = 0.63; excess abso lute risk (EAR) per 10(4) person-year sievert (PY Sv) = 29.7]. For can cers of the stomach (ERR(1 Sv) = 0.32), colon (ERR(1 Sv) = 0.72), lung (ERR(1 Sv) = 0.95), breast (ERR(1 Sv) = 1.59), ovary (ERR(1 Sv) = 0.9 9), urinary bladder (ERR(1 Sv) = 1.02) and thyroid (ERR(1 Sv) = 1.15), significant radiation associations were observed. There was some indi cation of an increase in tumors of the neural tissue (excluding the br ain) among persons exposed to the bombs before age 20. For the first t ime, radiation has been associated with liver (ERR(1 Sv) = 0.49) and n onmelanoma skin (ERR(1 Sv) = 1.0) cancer incidence in the LSS cohort. The present analysis also strengthened earlier findings, based on a sm aller number of cases, of an effect of A-bomb radiation on salivary gl and cancer. There was no significant radiation effect for cancers of t he oral cavity and pharynx as a group, esophagus, rectum, gallbladder, pancreas, larynx, uterine cervix, uterine corpus, prostate, kidney an d renal pelvis. Analyses of solid tumors individually and in combinati on revealed no appreciable differences between Hiroshima and Nagasaki (P > 0.5). The combined solid tumor analysis demonstrated a twofold gr eater relative risk for females than males and a trend for a decreasin g relative risk with increasing age at exposure (P < 0.001). Females h ad a higher relative risk of cancers of the lung, total respiratory sy stem and urinary system than males. The excess relative risk decreased with increasing age at exposure for combined digestive, stomach, nonm elanoma skin, breast and thyroid cancers. For solid cancers combined, the excess cancer risk increased with increasing attained age and was proportional to the background incidence rate. Unadjusted for age at e xposure, the excess relative risk for most sites tended to decrease wi th increasing attained age. For some cancers (colon, breast, central n ervous system and kidney) models that allowed the excess relative risk to vary with attained age fit at least as well as models that include d age-at-exposure effects. For all solid tumors, excess cancers increa sed with time since exposure, based on an absolute excess risk model. Averaged over all ages at exposure, the relative risk decreased with t ime since exposure. Examination of temporal patterns by age-at-exposur e groups suggested that the excess relative risk decreased with time f or the younger age-at-exposure groups and remained virtually constant for the older cohorts. The LSS has served as one of the major sources of data used for cancer risk estimation. Previous studies focused prim arily on the association between cancer mortality and radiation exposu re. Although these mortality studies are extremely valuable, the accur acy of cancer diagnoses is limited, and death certificates do not prov ide adequate information on cancers with relatively high survival rate s. Although incidence data also have their limitations (e.g., incomple te case ascertainment and partial reliance on death certificate diagno ses), they can provide more complete data on cancers with good surviva l, on histological type and on time from exposure to cancer onset. Thu s future analyses of atomic bomb survivors should focus on both cancer mortality and incidence.