2Studies of Cancer in Humans

2.1. Screening studies

Ward et al. (1988; 1990) reported three cases with noninvasive papillary tumours of the bladder identified in a screening study of 385 workers who had been exposed to MOCA in a chemical plant in Michigan, USA, from 1968 to 1979. Later on, Hogan (1993) assessed detailed occupational exposures for the three cases by reviewing the chemical plant’s product catalogues, material safety-data sheets, and written documentation about chemicals used to produce specific products, and by examining job histories, the time frames of exposure, and job classifications. The study found that the three cases had been exposed to many other chemicals in addition to MOCA during their time at the chemical plant and throughout their work history. Some of these chemicals are known or suspected bladder carcinogens (ortho-toluidine, 4-chloro-ortho-toluidine).

In 1989, Fox Chase Cancer Center worked with DuPont Chamber Works in New Jersey, USA to develop a bladder-cancer screening programme for the high-risk population of workers who had been exposed to MOCA, β-naphthylamine, benzidine, or ortho-toluidine at this plant (Mason and Vogler 1990; Mason et al. 1992). During the first seven quarterly periods of screening, two new cases and one recurrent case of transitional cell carcinoma of the bladder were detected, but they had been exposed to occupational bladder carcinogens other than MOCA.

Chen et al. (2005) screened for bladder cancer at four MOCA-manufacturing factories in Taiwan, China that employed 70 workers who were directly involved in MOCA-manufacturing processes, including the reaction, neutralization, washing, purification, and packing, or who were indirectly involved in the research and development laboratory. Ninety-two workers were not involved in the MOCA manufacturing or packing, nor were they working in the same building as the employees involved in these activities. The prevalence of atypical urinary cells and the nuclear matrix protein 22 tumour marker was not significantly different between the two groups of workers. However, the prevalence of positive occult blood was borderline-significantly (P = 0.055) greater in male exposed workers (18%) than in male non-exposed workers (7%). Among the 70 workers who had exposure to MOCA, there was one person with suspected malignant cells on urine cytology, one person with atypical cytology combined with gross haematuria, and one simply with atypical cytology. One worker was absent from the screening programme because he was admitted to the hospital, where he was diagnosed with bladder cancer. Liu et al. (2005) presented detailed information for the confirmed bladder-cancer case in his occupational history and environmental monitoring data. The confirmed bladder-cancer case had worked in the purification process area for 14 years (1987–2001), where the concentration of MOCA in the air was the highest (0.23–0.41 mg/m³) and exceeded permissible OSHA exposure levels (0.22mg/m³), without wearing any personal protective equipment at work. Furthermore, the worker was a non-smoker without a history of exposure to any other bladder carcinogen, except for occasional pesticides application during agricultural work before he began working at this factory.