Epidemiologic study for occupational bladder cancer in Japan.

1998 Fiscal Year Final Research Report Summary

• Project/Area Number: 09670364
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Hygiene
• Research Institution: KEIO UNIVERSITY
• Principal Investigator: KONDO Takefumi Keio University, School of Medicine, Professor, 医学部, 教授 (20234940)
• Co-Investigator(Kenkyū-buntansha): TACHIBANA Masaaki Keio University, Shool of Medicine, Assistant Professor, 医学部, 専任講師 (70129526) ; SHIMADA Naoki Keio University, School of Medicine, Assistant Professor, 医学部, 専任講師 (90255430)
• Project Period (FY): 1997 – 1998
• Keywords: occupational bladder cancer / benzidine / beta-naphthylamine / exposure period / latent period / Kaplan-Meier method / Cox's proportional hazard model / epidemiologic study

Research Abstract

The purpose of this study is to estimate the latent carcinogenic period of benzidine and beta-naphthylamine. Furthermore, this study reconsiders the importance of continuous close surveillance for the dyestuff workers who engaged in the manufacturing process of these chemicals.
In the first year of this study, we surveyed the incidence of bladder cancers in a group of 236 dyestuff plant workers who had been exposed to these dyestuffs from 1962 to 1996. Nineteen workers (8.1%) were found to have bladder cancers. The exposure period for these 19 tumor developments was 82.0(S.D : 50.2) months. The latent period from the subjects' initial and final exposure until tumor development was 29.5(S.D : 8.2) years and 20.1(S.D. : 1O.6) years respectively. Significantly, a negative correlation (Pearson) was observed between the exposure period and the latent period from the end of exposure to cancers' onset (R=-0.544, p<O.O5). Latent periods of these chemicals were longer than expected, and therefore, exposed workers must continue to be closely examined. Also, urine cytology is thought to be valuable for detecting and monitoring bladder tumors.
In the second year, we estimated the latent period using the data of 3109 men exposed to the dyestuffs. Firstly, we computed the cumulative incidence of the bladder cancer using Kaplan-Meier method, and plotted it against latency period. Secondly, we fitted the logistic curves to the scatter plot (i.e., to the relationship between cumulative incidence and latency period) repeatedly by varying the upper bounds. We decided that the upper bound of logistic curve where the correlation coefficient showed the highest value indicated the longest latency period. The longest latent period of bladder cancer caused by exposure to BZ was estimated at 51.3 years.
According to proportional hazards model analysis, exposure period and age at the initial exposure were confirmed to raise the risk of bladder cancer.