Figure 2.

Adjusted hazard ratios for premenopausal breast cancer incidence as a smoothed function of 20-year lagged cumulative synthetic metalworking fluid (MWF) as estimated in a Cox regression model using penalized splines (2 degrees of freedom) based on a cohort of female workers in the United Autoworker-General Motor incidence cohort who were alive in 1985, Michigan, 1985–2013. Premenopausal breast cancer was defined as diagnosis by four select age cut points. The 95% confidence interval (95% CI) is shown for the model using age 55 years as the cut point. Models used age as the time scale and adjusted for cumulative exposure to straight and soluble MWF, year of hire, calendar year, race, and manufacturing plant. Graph truncated at the 99th percentile of synthetic fluid exposure among cases (0.60 mg/m³-years). The rug plot indicates exposure of the cases 55 years old or younger.