Stem and progenitor-like cells contribute to the aggressive behavior of human epithelial ovarian cancer

The cellular mechanisms underlying the increasing aggressiveness associated with ovarian cancer progression are poorly understood. Coupled with a lack of identification of specific markers that could aid early diagnoses, the disease becomes a major cause of cancer-related mortality in women. Here we present direct evidence that the aggressiveness of human ovarian cancer may be a result of transformation and dysfunction of stem cells in the ovary. A single tumorigenic clone was isolated among a mixed population of cells derived from the ascites of a patient with advanced ovarian cancer. During the course of the study, yet another clone underwent spontaneous transformation in culture, providing a model of disease progression. Both the transformed clones possess stem cell-like characteristics and differentiate to grow in an anchorage-independent manner in vitro as spheroids, although further maturation and tissue-specific differentiation was arrested. Significantly, tumors established from these clones in animal models are similar to those in the human disease in their histopathology and cell architecture. Furthermore, the tumorigenic clones, even on serial transplantation continue to establish tumors, thereby confirming their identity as tumor stem cells. These findings suggest that: (a) stem cell transformation can be the underlying cause of ovarian cancer and (b) continuing stochastic events of stem and progenitor cell transformation define the increasing aggression that is characteristically associated with the disease.