Cancer incidence in female laboratory employees: extended follow-up of a Swedish cohort study.

OBJECTIVES: Work in chemical laboratories is associated with exposure to chemicals, of which some are known or suspected carcinogens. A cohort study of laboratory workers in Stockholm followed until 1992 showed an excess of hematolymphatic malignancies in chemical laboratories and an excess of breast cancer among women working for more than 10 years in such laboratories. The follow-up of this cohort has now been extended by 20 years.

METHODS: The cohort comprised 2245 female laboratory workers who are employed for >1 year from 1950 to 1989. Information on employment periods and type of laboratory ('chemical' or 'non-chemical') was obtained from employee registers. Cancer diagnoses from 1958 to 2012 were obtained from the Swedish Cancer Registry.

RESULTS: There were 383 cases of cancer (SIR=0.93 (95% CI 0.84 to 1.02)). The risk of breast cancer was elevated, of borderline statistical significance, among those who had worked for at least 10 years in chemical laboratories (SIR=1.41 (95% CI 0.99 to 1.95) 36 cases). The breast cancer risk was especially high in women who had worked for more than 10 years in chemical labs before 1970 (SIR=3.76 (95% CI 1.72 to 7.14), nine cases). There was no excess of breast cancer in non-chemical labs (SIR=0.77 (95% CI 0.54 to 1.07), 35 cases). The number of hematolymphatic cancer was no longer significantly elevated.

CONCLUSIONS: The increased risk of breast cancer, as well as the earlier noted excess of hematolymphatic malignancies, may be related to exposure to carcinogenic chemicals/organic solvents (eg, benzene) used in chemical laboratories, especially during earlier periods.