Table 4. Oligometastatic breast cancer.

1st Author, year [Ref]	Strength of evidence (study design /endpoint)	Prospective (P) or Retrospective (R)	Sample size	Definition-Oligometastases	Therapy	Endpoint	Conclusion
Kobayashi, 2012 [71]	3ii /A	R	75	1–2organs with met lesions, ≤5 lesions/organ, ≤5cm lesion diameter	+/− CT, then +/− local therapy + CT	10yr OS-59.2%; 20yr OS 34.1%	Prognosis of OMBC superior to that of MBC
Bojko, 2004 [69]	3iii / A	P	48	1 organ with 1-few met lesions	Surgery or RT + CT, then peripheral-blood-stem-cell transplant	MOS-42.2 mths	Combined modality therapy safe in OMBC; promising relapse-free survival
Milano, 2009 [70]	3iii / A	P	40	≤5 met lesions	Curative-intent SBRT	4yr OS-59%; MOS- NR	SBRT may yield prolonged survival + perhaps cure in select OMBC
Mimoto, 2014 [72]	3iii /A	R	14	1–2 organs with met lesions, ≤5 lesions/organ, ≤5cm lesion diameter	Surgery	10yr OS-59.2%, 20yr OS-34.1%; CD44+/CD24–/low tumor cells in 9% OMBC versus 73% non-OMBC	In OMBC, low levels of cancer-initiating cells may be associated with better prognosis
Vander Walde, 2012 [73]	3iii /A	R	12	≤3 sites	CT, then peripheral stem cell rescue	3-yr OS- 73%	Therapy was safe
Nieto, 2002 [75]	3iii /A	R	60	Low tumor burden, w met lesion could be either excised en bloc before HDC, or encompassed w a single RT field w curative intent.	CT	MOS- 80 mths; 5-yr OS 62%	Possibly re-evaluate current tenet that early detection MBC is of no benefit
Bourgier, 2010 [74]	3iii /D	R	159	1 met site	RT versus RT + surgery	3yr OS- RT- 39% versus RT+ surg-57%; equivalent when adjusted for prognostic factors	In sub-analysis, OMBC had better metastatic PFS as compared to patients with >1 met site

Abbreviations: Met(s) = metastasis (es); CT = chemotherapy; yr = year; OS = overall survival; OMBC = oligometastatic breast cancer; MBC = metastatic breast cancer; RT = radiation therapy; MOS = median overall survival; NR = not reached; mths = months; SBRT = stereotactic body radiation therapy; HDC = high dose chemotherapy; PFS = progression free survival