Occupational heat exposure may promote breast cancer

Women exposed to heat at their workplaces risk developing breast cancer, according to a study.

The large case–control study involved 1,389 breast cancer patients and 1,434 frequency-matched population controls. Patients tended to be younger (54.9 vs 57.2 years), were less frequently postmenopausal (61.6 percent vs 67.0 percent), and had lower parity. On the other hand, more controls had never smoked (55.2 percent vs 51.1 percent) and fewer reported a family history of breast cancer (8.9 percent vs 15.5 percent).

A job-exposure matrix, MatEmEsp, was used to estimate the proportion of workers exposed at least 1 year to and work time with heat stress (wet bulb globe temperature ISO 7243) for each occupation. About 26.7 percent of the patients and 21.9 percent of controls had occupational heat exposure, with an average duration of 10.6 years. Jobs with the highest exposure included operators of furnaces, mining labourers, launderers and ironers, and cooks and other food preparers.

In logistic regression models, ever occupational heat exposure conferred a modest but meaningful increase in the risk of breast cancer (odds ratio [OR], 1.22, 95 percent confidence interval [CI], 1.01–1.46), with significant trends across categories of lifetime cumulative exposure and duration (p_trend=0.01 and p_trend=0.03, respectively).

Of note, a stronger association was seen for hormone receptor–positive disease (ever exposure: OR, 1.38, 95 percent CI, 1.12–1.67).

There were no confounding effects from multiple other common occupational exposures. However, results were attenuated after adjustment for occupational detergent exposure.