Work in chemical laboratories may potentially be associated with exposure to carcinogenic chemicals. A previous cohort study of laboratory technicians in Stockholm followed until 1992 showed an excess of hematolymphatic malignancies among workers in chemical laboratories and an excess of breast cancer among women working for more than 10 years in such laboratories.
The cohort comprised laboratory technicians employed 1950–1989 at “chemical” (e.g. chemistry, cytology, pathology) or “non-chemical” (e.g. physiology, haematology, fertility) laboratories at Karolinska Hospital and Karolinska Institutet in Stockholm. Follow-up of the 2 247 women in the cohort was extended by 20 years to include the period 1958–2012. Information on employment times and types of laboratory work was obtained from employee registers. Cancer incidence data was obtained from the the Swedish Cancer Registry.
There were 389 cases of cancer in the cohort, SIR = 0.94 (95% CI: 0.85–1.04). The risk of breast cancer was increased among those who had worked for at least 10 years in chemical laboratories, SIR = 1.49 (1.05–2.05), 38 cases. There was no excess of breast cancer among those who had worked in non-chemical labs (SIR = 0.77 (0.54–1.07), 35 cases. The number of hematolymphatic cancers was not significantly increased.
The increased risk of breast cancer among women who had worked for at least 10 years in chemical labs may be related to exposure to cancerogenic chemicals used in these laboratories. The absence of risk among those working in non-chemical labs makes it less likely that the excess would be caused by diagnostic bias resulting from a higher participation in mammography screening among health care workers, or late or no child-births due to longer education, since these factors would be expected to be similar between chemical and non-chemical labs. Night work, a well-recognised risk factor for breast cancer, is uncommon for lab workers.