Cancer morbidity among employees in a Danish pharmaceutical plant

Workers in the pharmaceutical industry may be exposed to many potential carcinogens. We investigated cancer morbidity in a Danish plant where enzymes, insulin, antibiotics and sex hormones were produced in substantial quantities.

Altogether 10,889 people ever employed (1964-1988) at the pharmaceutical plant were retrieved from the files of a compulsory pension fund, and followed-up in the nationwide Danish Cancer Registry (1964-1989). Site-specific standardized incidence ratios (SIR) were estimated, based on cancer rates for the national population. Information on risk factors for breast cancer, e.g. number of children, age at menarche and first delivery, obesity, and non-occupational use of sex hormones was obtained from samples of the female employees, and compared to equivalent variables from the general population.

The overall SIR for women was significantly elevated (n = 5554; SIR = 1.2). Excess risk was particularly seen for breast cancer (n = 97; SIR = 1.5), especially in a subgroup who had started work at the factory aged 30-39 and had continued to work for 1-9 years (SIR = 2.8). The SIR was near unity for men (n = 5335); however, three men with breast cancer versus 0.4 expected were found. Lifestyle components explained only about one-quarter of the excess female breast cancers. Proxy measures of intensity of occupational exposure to sex hormones or insulin showed no association with the risk for breast cancer.

It seems unlikely that either a single occupational factor or an unusual reproductive pattern can explain the elevated breast cancer risk. Therefore, the finding requires further study.