Tumor cell dormancy: an NCI workshop report.

The long latency period that occurs in some patients between initial treatment and evidence of metastases is attributed to tumor cell dormancy. Although the clinical occurrence of these late developing metastases has intrigued the medical community for years, there's a paucity of experimental data, especially among the solid tumors. Of clinical importance is that dormant tumor cells are highly refractory to chemotherapy. For these reasons, the NIH convened a small workshop in July 2006 of investigators with interests in this field to review the challenges and research opportunities. This report summarizes the key outcomes of this workshop. The mechanisms associated with tumor cell dormancy are poorly defined, in part because the dormant tumor cells have been extraordinarily difficult to isolate. New isolation and characterization techniques were presented. One of the critical limitations confronting the field is that molecular markers of dormancy are not now known. The workshop considered the role of the microenvironment in promoting and maintaining dormant tumor cells as well as events in the microenvironment that could activate the dormant cells. There was also discussion of new models of dormancy and new imaging modalities. Furthermore, the workshop reviewed studies of hematological tumor cell dormancy and how this insight could best be applied to the solid tumors. Finally, there was discussion related to the design of clinical trials for the study of tumor cell dormancy. The workshop concluded with an overall summary of the challenges and research opportunities associated with this field with recommendations for consideration by the NIH.