Sarcoma Stem Cells: Do We Know What We Are Looking for?

Table 2

Studies showing isolation of sarcoma-initiating cells.

Tumor Type	Technique	Summary of findings	Reference
Osteosarcoma		CD133+ cells demonstrated increased sphere formation, growth in soft agar, expression of OCT3/4, and presence of side population
	CD133		[21, 22]
			Double positive (CD117+ and Stro-1+) cells were seen with a higher incidence in spheres, and they showed higher tumorigenicity as well as chemoresistance
	CD117, Stro-1	[23]
		ALDH-high cells isolated from xenografts established from cell line OS99-1 had increased tumorigenicity, self-renewal, and ability to produce differentiated progeny, and expressed increased levels of OCT3/4A, NANOG, and SOX-2
	ALDH		[24]
			SP was seen in 1 of 7 osteosarcoma cell lines tested. SP population had increased sphere- and colony-forming activity and increased tumorigenicity
	SP			[25]
	Ewing’s sarcoma				CD133+ cells showed increased tumorigenicity, ability to establish a heterogeneous population and differentiation, and increased expression of OCT4, SOX2, and NANOG. There was a correlation in primary tumors between higher expression of CD133 and chemoresistance
		CD133	[26–28]
			ALDH-high cells showed increased sphere- and colony-forming ability, chemoresistance, SP, and tumorigenicity
		ALDH		[35]
		Rhabdomyosarcoma				Serial passages of rhabdomyosarcoma spheres enriched for cells with increased expression of OCT4, NANOG, c-Myc, SOX2, and PAX3 and increased expression of CD133 and CD133+cells showed increased tumorigenicity, ability to Differentiate, and chemoresistance. CD133 expression also correlated with poorer survival in patient samples
			CD133	[30]
Synovial sarcoma				5 of 5 primary tumor samples and 3 of 3 cell lines demonstrate a CD133+ subpopulation, but not TIC properties were tested
			CD133		[31]
	Multiple sarcomas				Size of SP in primary tumor samples correlated with tumor grade. SP cells from 1 osteosarcoma, 1 synovial sarcoma, and 2 malignant fibrous histiocytosis samples showed increased tumorigenicity and ability to produce a heterogeneous cell population (SP and nonSP)
SP			[32]