Table 3.

Effect of adjuvant beam radiation therapy for overall survival in different age groups.

	Crude model		Adjust model I		Adjust model II
	HR (95% CI)	p	HR (95% CI)	p	HR (95% CI)	p
Age ≤ 55 years old	0.51 (0.26, 1.02)	0.058	0.49 (0.25, 0.97)	0.042	0.49 (0.25, 0.99)	0.045
Age > 55 years old	1.20 (0.94, 1.53)	0.152	1.59 (1.23, 2.06)	<0.001	1.52 (1.17, 1.98)	0.002
P for interaction		0.015		0.001		0.001

The Hazard ratios (HR) of adjuvant beam radiation therapy (ABRT) intervention were calculated with Cox proportional hazards model in different age groups. Interaction analyses were conducted for ABRT and age group on overall survival in different models.

Crude model: adjust for none.

Adjust model I: adjust for demographic variables including: gender, race, age, and marital status.

Adjust model II: adjust for demographic, tumor, and treatment variables including: gender, race, age, marital status, tumor size, laterality, primary site, and surgery type.