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

Table 2 Retrospective studies published within the last decade investigating the impact of locoregional treatment to the primary tumor site in de novo metastatic breast cancer

Ref.	n	Treatment	Patient	Median follow-up (mo)	Outcomes
Ma et al[35]	987	Surgery (n = 463)	Surgery arm: More T1-2, HR-positive, solitary metastasis, bone only metastasis	NR	Median survival (mo): 45 vs 28, P < 0.001
		No surgery (n = 524)
					Better survival in surgery after systemic therapy than primary surgery
					Triple negative, brain metastases: No benefit of surgery
Lane et al[16] (NCDB)	24015	Systemic therapy alone (n = 13505)	Surgery after systemic therapy arm: Younger, more T3-4 and HR-negative	NR	Median OS (mo): 37.5 vs 49.4 vs 52.8, P < 0.001
		Surgery before systemic therapy (n = 4552)			RT: No impact on OS
		Systemic therapy before surgery (n = 5958)
Li et al[36] (SEER database)	20870	Surgery (n = 5779)	Surgery arm: Younger, more T1-3, N+, Gr III, and less HR+	NR	Surgery arm (± RT): Improved BCSS and OS (P < 0.001)
		No surgery (n = 15091)
			More chemo and RT received
Pons-Tostivint et al[37]	4276	LRT (n = 1706): Surgery, RT or both	LRT arm: Younger, more solitary or bone-only metastases	45.3	Median OS (mo): HR-positive, HER2- negative: 61.6 vs 45.9, P < 0.001
		No LRT (n = 2570)			HR-positive, HER2-positive: 77.2 vs 52.6, P = 0.008
					Triple negative: 19 vs 18.6, P = 0.54
					Bone only metastases: 70.4 vs 62, P < 0.001
					Visceral metastases: 83 vs 52.7, P < 0.001
Choi et al[38]	245	LRT (n = 82): Surgery, RT or both	LRT arm: < T4, no liver or brain metastasis, and < 5 metastatic sites	40	5-yr LRFS: 62% vs 20%, P < 0.001
					5-yr OS:73% vs 45%, P = 0.02
		No LRT (n = 163)
Gultekin et al[7]	227	LRT (n = 188): Surgery, RT or both	LRT arm: Less T3-4 and more solitary metastases	35	5-yr OS: 56% vs 24%, P < 0.001
					5-yr PFS: 27% vs 7%, P < 0.0001
		No LRT (n = 39)
Nguyen et al[39]	733	LRT (n = 378): Surgery, RT or both	LRT arm: Younger, more T1-2, N0-1, limited M1 disease	21	5-yr OS: 21% vs 14%, P < 0.001
					5-yr PFS 72% vs 46%, P < 0.001
		No LRT (n = 355)
Neuman et al[25]	186	Surgery (n = 69): 13% RT	Surgery arm: More HER2-negative, smaller tumors, more solitary metastasis	52	No difference in OS (P = 0.10)
		No surgery (n = 117)

NCDB: National Cancer Database; SEER: Surveillance, Epidemiology, and End Results, RT: Radiotherapy; LRT: Locoregional treatment; T: Tumor; HR: Hormone receptor; HER2: Human epidermal growth factor receptor 2; N: Node, Gr: Grade; M: Metastasis; NR: Not reported; OS: Overall survival; PFS: Progression-free survival; BCSS: Breast cancer-specific survival; LRFS: Local recurrence-free survival.