Development and validation of an extended Cox prognostic model for patients with ER/PR+ and HER2− breast cancer: a retrospective cohort study

Table 8 An interaction effect between age and PR for patients aged ≥ 41 years and PR ≥ 20% after 164-week postoperation

The different time periods	Prognostic factor				Coefficient	HR
< 164-week postoperation	PR status	Low			0.00	1.00
	PR status	High			−1.80	0.17
	Age^a	Young			0.00	1.00
		Middle aged			−1.56	0.21
		Elderly			−0.19	0.83
≥ 164-week postoperation	PR status	Low	Age^a	Young	0.00	1.00
				Middle aged	−1.56	0.21
				Elderly	−0.19	0.83
		High	Age^a	Young	−1.80	0.17
				Middle aged	−1.77	0.17
				Elderly	−0.39	0.68

HR hazard ratio. ^aRegarding age, the patients were divided into three groups: young (< 41 years old), middle aged (41–55 years old), and elderly (55 and older)

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