Abstract
Primary lung cancer is the leading cause of cancer-related deaths in most industrialized countries, and it is important to detect and control metastases distant from the lungs for improvement of a patient's prognosis. Circulating tumor cells (CTCs) are tumor cells that are shed from the primary site and circulate in the peripheral blood, and recent studies have shown that CTCs can be useful clinical markers in some solid tumors such as those of breast cancer. In primary lung cancer, the clinical significance of CTCs remains unclear, but some promising results have been recently reported. Here, we reviewed the current status and future perspectives of CTCs in primary lung cancer.