Various Factors Contributing to Tumor Dormancy: Therapeutic Implications in Breast Cancer

Cancer dormancy describes a stage in tumor progression where tumor cells survive in a quiescent state. Breast cancer is especially known for prolonged asymptomatic periods (up to 15–20 years) followed by a recurrence. Two main mechanisms of tumor cell dormancy are under discussion: tumor cells cease dividing completely or persist proliferating at a slow rate counterbalanced by apoptosis. In the last decades, major efforts have been made to understand the process of interaction between circulating tumor cells (CTCs) in the bloodstream and their extravasation into distant sites, where CTCs may survive in a dormant state or acquire the ability to build metastases. Despite remarkable progress in this field, factors that determinate the fate of a single tumor cell remain to be clarified.