Role of radiotherapy in oligometastatic breast cancer: Review of the literature

Table 3 Retrospective studies investigating the role of radiotherapy as a local treatment of metastases in oligometastatic disease

Ref.	n	Treatment	Patients	Median follow-up (mo)	Outcomes
Weykamp et al[28]	46	SBRT: Bone, lung, liver, adrenal gland	Inclusion criteria: breast cancer, oligometastatic (≤ 3) or oligoprogressive (1) disease	21	2-yr LC, DC, PFS and OS: 89%, 44%, 17%, and 62%, respectively
		Median 3 frx (1-10)/28 Gy (24-60 Gy)
					Solitary metastasis: Poor prognostic factor for DC and PFS
			58 lesions
					Higher age: Poor prognostic factor for OS
Kobayashi et al[29]	75	Primary systemic chemotherapy: CR/PR	Inclusion criteria: breast cancer, ≤ 2 metastatic organs, < 5 metastases, < 5 cm lesions	103	10-yr and 20-yr OS: 59.2% and 34.1%, respectively
		Surgery or RT			10-yr and 20-yr RFS: 27.4%
					Single organ metastasis, local treatment and shorter DFI: Better RFS
Hong et al[4]	361	SBRT	Extracranial oligometastases (≤ 5)	26.2	3-yr OS, PFS and TMC were 56%, 24%, and 72%, respectively
		10 frx/50-60 Gy or 3 frx/24-48 Gy
			Breast cancer (16%)
					Primary tumor type, interval to metastasis, number of treated metastasis, and mediastinal/hilar LN, liver, or adrenal metastases: Associated with OS
					All breast cancer patients: RPA class 1 (3-yr OS 75%)
Cha et al[40]	49	Endocrine therapy plus LRT (n = 33)	Inclusion criteria: HR-positive, HER2-negative	101.6 vs 105.6	Median OS (mo): 72.3 vs 91, P = 0.272
		82% RT: Bone, LN
		Endocrine therapy alone (n = 16)
					Median PFS (mo): 30 vs 18, P = 0.049
			Similar patient and tumor characteristics

SBRT: Stereotactic body radiation therapy; frx: Fraction, Gy: Gray, CR: Complete response; PR: Partial response; RT: Radiotherapy; LN: Lymph node; LRT: Locoregional treatment; HR: Hormone receptor; HER2: Human epidermal growth factor receptor 2; LC: Local control; DC: Distant control; OS: Overall survival; PFS: Progression-free survival; DFI: Disease-free interval; TMC: Treated metastasis control; RPA: Recursive partitioning analysis.