Table 2.

Main survival analysis, showing adjusted hazard ratios and survival rates relative to percent mammographic density (PMD), with the corresponding 95% confidence intervals (in brackets) resulting from the reduced model.

Outcome	PMDa	Hazard ratiob (95% CI)	5-year survival ratec (95% CI)	10-year survival ratec (95% CI)
DFS	Low (13%)	1 (reference)	0.87 (0.85,0.90)	0.76 (0.71,0.81)
	Intermediate (35%)	0.90 (0.59,1.21)	0.89 (0.86,0.91)	0.78 (0.75,0.82)
	High (65%)	0.84 (0.51,1.17)	0.89 (0.87,0.92)	0.79 (0.75,0.83)
OS	Low (13%)	1 (reference)	0.91 (0.89,0.93)	0.81 (0.77,0.85)
	Intermediate (35%)	0.89 (0.54,1.23)	0.92 (0.90,0.94)	0.83 (0.80,0.86)
	High (65%)	0.80 (0.43,1.17)	0.93 (0.91,0.95)	0.84 (0.81,0.88)

CI, confidence interval; DFS, disease-free survival; OS, overall survival.

^aPMD was regarded as a continuous predictor and used as a natural spline with two degrees of freedom. It was evaluated at the 10th percentile (“low”), median (“intermediate”), and 90th percentile (“high”). The percentiles were chosen arbitrarily for the purpose of describing results. The underlying statistical model is not affected of that choice.

^bHazard ratios and survival rates were estimated using the reduced Cox regression model, with the following predictors: age at diagnosis (<55 and ≥ 55 years), year of diagnosis (before and after 2006), body mass index (<25, 25–30, and ≥30 kg/m²), tumor stage (pT1 to pT4), grading (grade 1 and 2 versus grade 3), lymph node status (pN0 and pN+), estrogen receptor status (ER, positive and negative), progesterone receptor status (PR, positive and negative) and HER2 status (positive and negative).

^cSurvival rates were estimated for an “average” patient — i.e., a patient belonging to the most frequent categories (age ≥ 55 years, year of diagnosis before 2006, BMI < 25 kg/m², pT1, grading 1 or 2, pN0, ER-positive, PR-positive, HER2-negative).