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

Table 4 Prospective studies exploring the role of radiotherapy to metastatic sites in oligometastatic disease including primary breast cancer

Ref.	n	Treatment	Patients	Median follow-up (mo)	Outcomes
Palma et al[5] (SABR-COMET)	99	Palliative RT ± systemic therapy (n = 33)	Inclusion criteria: 1-5 metastases, life expectancy ≥ 6 mo, controlled primary tumor	51	5-yr OS: 17.7% vs 42.3%, P = 0.006
					4-yr PFS 3.2% vs 21.6%, P = 0.001
		1 frx/8 Gy or 10 frx/30 Gy
					LC 46% vs 63%, P = 0.039
		SABR ± systemic therapy (n = 66)
					≥ Gr 2 toxicity: 9% vs 29%, P = 0.026
			Primary breast cancer (n): 5 vs 13
		Different regimens according to tumor size and location			SABR: Gr 5 toxicity (n = 3)
Milano et al[9]	48	HSRT: ≥ 50 Gy in 10 frx	Inclusion criteria: breast cancer, 1-5 extracranial metastases, primary controlled	52	5- and 10-yr OS:
					Bone-only oligometastases: 83% and 75%
					Non-bone-only oligometastases: 31% and 17% (P = 0.002)
					GTV > 25 cc: Poor prognostic factor for LC
Trovo et al[6]	54	SBRT: 3 frx/30-45 Gy (n = 44)	Inclusion criteria: breast cancer, ≤ 5 extracranial metastases, primary controlled	30	2-y LC: 97%
					2-y OS: 95%
		IMRT: 25 frx/60 Gy (n = 10)			1- and 2-yr PFS: 75% and 53%, respectively
					No ≥ Gr 3 toxicity
			92 lesions
Salama et al[26]	61	SBRT: Lung, LN, liver, bone, adrenal, soft tissue, pancreas	Inclusion criteria: 1-5 metastatic sites, life expectancy > 3 mo	20.9	1-yr and 2-yr OS: 81.5% and 56.7%, respectively
					1-yr and 2-yr PFS: 33.3% and 22.0%, respectively
		3 frx/24-48 Gy	Breast cancer (11.3%)
Scorsetti et al[31]	33	SBRT: 3-4 frx/48-75 Gy	Inclusion criteria: breast cancer, < 5 lung or liver metastases, other metastatic sites stable or responding after chemotherapy	24	1- and 2-yr LC: 98% and 90%, respectively
					1- and 2-yr OS: 93% and 66%, respectively
					1- and 2-yr PFS: 48% and 27%, respectively
					No grade 3-4 toxicities
			43 lesions
Milano et al[30]	40	SBRT doses and fractionation was not mentioned	Inclusion criteria: breast cancer, ≤ 5 metastases	NR	4-yr OS: 59%
					4-yr PFS: 38%
					4-yr LC: 89%
					Favorable prognosis: Solitary metastasis, smaller tumor volume, bone-only disease, and stable or regressing lesions

RT: Radiotherapy; frx: Fraction; Gy: Gray; SBRT: Stereotactic body radiation therapy; HSRT: Hypofractionated stereotactic radiotherapy; IMRT: Intensity-modulated radiation therapy; NR: Not reported; OS: Overall survival; PFS: Progression-free survival; LC: Local control; LN: Lymph node; Gr: Grade; GTV: Gross tumor volume.