Table 3.

Prognostic factors for local control

Local control		Univariable analysis			Multivariable analysis
		HR	95% CI	P-value	HR	95% CI	P-value
Age	(< 45 vs. ≥ 45 years)	1.07	0.58–1.96	0.832
Subtype	(HR positive vs. HER2 positive)	1.79	0.95–3.37	0.070
	(HR positive vs. TN)	1.08	0.56–2.07	0.825
Treatment year	(continuous)	0.94	0.88–1.02	0.126
Treatment era	(2010–2015 vs. 2016–2021)	0.63	0.37–1.07	0.089
Previous systemic treatment	(≤ 2 vs. > 2 lines)	2.81	1.64–4.81	< .001	2.84	1.50–5.36	0.001
Interval from diagnosis to PRT	(≤ 1 vs. > 1 year)	1.68	0.99–2.85	0.055
Number of metastatic lesions	(≤ 5 vs. > 5 lesions)	1.64	0.59–4.54	0.340
Disease status	(de novo stage IV vs. recurrent stage IV)	1.83	0.90–3.70	0.094	0.80	0.34–1.89	0.612
	(de novo stage IV vs. progressive Stage IV)	2.64	1.11–6.31	0.028	1.55	0.60–4.03	0.366
Disease burden outside breast	(SD vs. PD/mixed response)	2.47	1.33–4.58	0.004	2.20	1.15–4.20	0.009
Reason for breast PRT	(Symptomatic vs. asymptomatic)	1.47	0.83–2.61	0.184
Concurrent treatment	(No vs. hormonal therapy)	0.71	0.35–1.46	0.354
	(No vs. anti-HER2 therapy)	0.83	0.31–2.22	0.712
	(No vs. cytotoxic chemotherapy)	1.35	0.71–2.54	0.357
Gross tumor volume	(Continuous, per 100 cc)	1.01	0.97–1.05	0.606
Gross tumor volume	(< 1260 vs. ≥ 1260 cm3)	1.63	0.89–2.98	0.114	1.62	0.86–3.05	0.136
PRT dose, EQD2	(< 63 vs. ≥ 63 Gy)	0.40	0.20–0.82	0.012	0.42	0.20–0.88	0.017
PRT modality	(3D-CRT vs. IMRT/proton therapy)	0.76	0.44–1.31	0.332

HR Hormone receptor, HER2 Human epidermal growth factor receptor 2, TN Triple-negative, SD Stable disease, PD Progressive disease, PRT Palliative radiation therapy, EQD2 Equivalent dose in 2 Gy fractions (α/β = 3.5); 3D-CRT, 3 dimensional-conformal radiation therapy, IMRT Intensity-modulated radiation therapy