Pancreatic cancer stem cells.

Cellular heterogeneity in cancer was observed decades ago by studies in mice which showed that distinct subpopulations of cells within a tumor mass are capable of driving tumorigenesis. Conceptualized from this finding was the stem-cell hypothesis for cancer, which suggests that only a specific subset of cancer cells within each tumor is responsible for tumor initiation and propagation, termed tumor initiating cells or cancer stem cells (CSCs). Recent data has been provided to support the existence of CSCs in human blood cell-derived cancers and solid organ tumors of the breast, brain, prostate, colon, and skin. Study of human pancreatic cancers has also revealed a specific subpopulation of cancer cells that possess the characteristics of CSCs. These pancreatic cancer stem cells express the cell surface markers CD44, CD24, and epithelial-specific antigen, and represent 0.5% to 1.0% of all pancreatic cancer cells. Along with the properties of self-renewal and multilineage differentiation, pancreatic CSCs display upregulation of important developmental genes that maintain self-renewal in normal stem cells, including Sonic hedgehog (SHH) and BMI-1. Signaling cascades that are integral in tumor metastasis are also upregulated in the pancreatic CSC. Understanding the biologic behavior and the molecular pathways that regulate growth, survival, and metastasis of pancreatic CSCs will help to identify novel therapeutic approaches to treat this dismal disease.