Table 3 Prognostic factors for local control

Age

(< 45 vs. ≥ 45 years)

0.58–1.96

0.832

Subtype

(HR positive vs. HER2 positive)

0.95–3.37

0.070

(HR positive vs. TN)

0.56–2.07

0.825

Treatment year

(continuous)

0.88–1.02

0.126

Treatment era

(2010–2015 vs. 2016–2021)

0.37–1.07

0.089

Previous systemic treatment

(≤ 2 vs. > 2 lines)

1.64–4.81

 < .001

1.50–5.36

Interval from diagnosis to PRT

(≤ 1 vs. > 1 year)

0.99–2.85

0.055

Number of metastatic lesions

(≤ 5 vs. > 5 lesions)

0.59–4.54

0.340

Disease status

(de novo stage IV vs. recurrent stage IV)

0.90–3.70

0.094

0.34–1.89

(de novo stage IV vs. progressive Stage IV)

1.11–6.31

0.028

0.60–4.03

Disease burden outside breast

(SD vs. PD/mixed response)

1.33–4.58

0.004

1.15–4.20

Reason for breast PRT

(Symptomatic vs. asymptomatic)

0.83–2.61

0.184

Concurrent treatment

(No vs. hormonal therapy)

0.35–1.46

0.354

(No vs. anti-HER2 therapy)

0.31–2.22

0.712

(No vs. cytotoxic chemotherapy)

0.71–2.54

0.357

Gross tumor volume

(Continuous, per 100 cc)

0.97–1.05

0.606

Gross tumor volume

(< 1260 vs. ≥ 1260 cm³)

0.89–2.98

0.114

0.86–3.05

PRT dose, EQD2

(< 63 vs. ≥ 63 Gy)

0.20–0.82

0.012

0.20–0.88

PRT modality

(3D-CRT vs. IMRT/proton therapy)

0.44–1.31

0.332