Occupational Heat Exposure and Breast Cancer Risk in the MCC-Spain Study

Cancer Epidemiol Biomarkers Prev. 2021 Feb;30(2):364-372. doi: 10.1158/1055-9965.EPI-20-0732. Epub 2020 Dec 2.


Background: Mechanisms linking occupational heat exposure with chronic diseases have been proposed. However, evidence on occupational heat exposure and cancer risk is limited.

Methods: We evaluated occupational heat exposure and female breast cancer risk in a large Spanish case-control study. We enrolled 1,738 breast cancer cases and 1,910 frequency-matched population controls. A Spanish job-exposure matrix, MatEmEsp, was used to assign estimates of the proportion of workers exposed (P ≥ 25% for at least 1 year) and work time with heat stress (wet bulb globe temperature ISO 7243) for each occupation. We used three exposure indices: ever versus never exposed, lifetime cumulative exposure, and duration of exposure (years). We estimated ORs and 95% confidence intervals (CI), applying a lag period of 5 years and adjusting for potential confounders.

Results: Ever occupational heat exposure was associated with a moderate but statistically significant higher risk of breast cancer (OR 1.22; 95% CI, 1.01-1.46), with significant trends across categories of lifetime cumulative exposure and duration (P trend = 0.01 and 0.03, respectively). Stronger associations were found for hormone receptor-positive disease (OR ever exposure = 1.38; 95% CI, 1.12-1.67). We found no confounding effects from multiple other common occupational exposures; however, results attenuated with adjustment for occupational detergent exposure.

Conclusions: This study provides some evidence of an association between occupational heat exposure and female breast cancer risk.

Impact: Our results contribute substantially to the scientific literature. Further investigations are needed considering multiple occupational exposures.

Publication types

  • Multicenter Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Breast Neoplasms / epidemiology
  • Breast Neoplasms / etiology*
  • Case-Control Studies
  • Female
  • Hot Temperature*
  • Humans
  • Middle Aged
  • Occupational Diseases / epidemiology
  • Occupational Diseases / etiology*
  • Occupational Exposure / adverse effects*
  • Risk Factors
  • Spain / epidemiology