Table 1. Phenotypic Identity and Estimated Frequency of CSCs in Various Tumor Entities.
Generally, CSCs from hematological malignancies are better characterized which is likely the result of the decade-long research in the field of hematopoiesis as a paradigm for stem cell biology. Hence, the molecular signature of these cells is well-characterized and strategies to re-sensitize them to treatment are already being explored [186, 187]. Conversely, CSCs from solid tumors remain much more elusive, entailing ambiguous phenotypic identities and significant challenges for drug development in most tumor types. Nevertheless, CSCs from both hematological malignancies and solid tumors share many characteristic properties including clonogenicity, tumor-initiating potential, asymmetric cell division, activation of (embryonic) stem cell pathways, detoxification/drug resistance, niche dependence, and their implication in disease recurrence. Note that this table is intended to exemplify the differences and similarities between various CSC populations and also depict their elusive nature and the difficulties in defining them. Accordingly, this table does not claim completeness. ‘Very low’, ‘low’ and ‘int to high’ represent CSC frequencies of <1%, 1-10% and >10%, respectively. CSC frequencies are not directly comparable between studies owing to differences in methodology and/or sampled material. ALDH, aldehyde dehydrogenase; CSC, cancer stem cell; SP, side population.
| Tumor Entity | Marker Signature of CSCs | Frequency | Reference |
|---|---|---|---|
| Blood Cancers | |||
| Acute lymphoid leukemia | CD34+/CD38-/CD19+ | low | [188] |
| Acute myeloid leukemia | CD34+/CD38- | low | [107] |
| Chronic myeloid leukemia | CD34+ | ―― | [14] |
| CD34+/CD38-/CD90+ | ―― | [189] | |
| CD34+/CD38-/CD26+ | very low | [190] | |
| Hodgkin lymphoma | CD27+/ALDH+/(CD19+/CD20+) | very low | [191] |
| Multiple myeloma | CD138-/CD34-/(CD19+/CD20+) | low | [192] |
| Myelodysplastic syndrome | CD34+/CD38-/CD90+ | very low | [193] |
| Solid Tumors | |||
| Bone sarcoma | Stro-1+/CD105+/CD44+ | ―― | [194] |
| CD133+ | low | [195] | |
| SP+ | low | [196] | |
| Breast cancer | CD44+/CD24- | low | [6] |
| Colorectal cancer | CD133+ | low | [133] |
| Lgr5+ | low | [135] | |
| Wnt+ | ―― | [134] | |
| CD44+ | low | [132] | |
| Krt19+/Lgr5- | ―― | [131] | |
| ALDH+ | low | [44] | |
| Glioblastoma | CD133+ | int to high | [197] |
| Hepatocellular carcinoma | CD133+/CD44+ | low | [198] |
| CD90+/CD44+ | low | [199] | |
| EpCAM+ | low | [200] | |
| Lung cancer | CD133+ | int to high | [125] |
| ALDH+ | low | [127] | |
| CD44+ | ―― | [128] | |
| CD117+ | ―― | [129] | |
| CD90+ | very low | [130] | |
| SP+ | low | [126] | |
| Medulloblastoma | CD133+ | int to high | [197] |
| Melanoma | ABCB5+ | int to high | [139] |
| CD271+ | int to high | [201] | |
| CD20+ | low | [202] | |
| Ovarian cancer | CD44+/CD24+ | very low | [118] |
| CD44+/CD24- | ―― | [119] | |
| CD44+/CD117+ | very low | [120] | |
| CD24+ | ―― | [121] | |
| ALDH+/CD133+ | very low | [123] | |
| ALDH+ | int to high | [124] | |
| SP+ | low | [37] | |
| Pancreatic cancer | CD44+/CD24+ | very low | [203] |
| Prostate cancer | CD44+/CD24- | low | [204] |
| SP+ | very low | [205] | |
| Renal cell carcinoma | CD105+ | low | [206] |