Cancer stem cells (CSCs) are defined as cells with self‑renewal ability, tumor‑initiating capacity, and the ability to give rise to more differentiated progeny. Though the frequency of these cells may vary among various kinds of tumors, they often represent a minor subset of tumor cells endowed exclusively with tumor‑initiating ability. CSCs in various cancers are mainly identified using cell‑surface markers expressed on corresponding normal stem cells. CSCs are frequently enriched in advanced and aggressive tumors, and cells isolated from distant metastases often show a CSC phenotype. In pancreatic cancer, a metastasis specific subset of CSCs (mCSCs) was identified and characterized with a CD133+CXCR4+ cell phenotype. Depleting these cells from the tumor inhibited tumor metastasis, providing evidence for a CSC role in mediating cancer metastasis. In several cases, residual tumors left after conventional cancer therapy showed enriched CSCs, which were often found to arbitrate resistance response to radiation and chemotherapy. Hence, it is essential to identify and characterize CSCs to develop new cancer therapeutics, which target this population.