Solitary cancer cells as a possible source of tumour dormancy?

Metastasis can occur many years after primary tumour treatment. However, the status of the tumour during this period of dormancy is poorly understood. As part of our ongoing experimental studies on mechanisms of metastasis, we have discovered that large numbers of disseminated single cells may persist in secondary sites for extended time periods. Identification of these cells was facilitated by in vivo techniques developed to quantify the fate of individual cells during the metastatic process. Here we review these in vivo techniques and findings. We also discuss the potential clinical implications if dormant solitary cells exist in appreciable numbers in cancer patients.