chapter  11
Circulating Tumor Cells in Individualizing Breast Cancer Therapy
ByJames M. Reuben, Massimo Cristofanilli
Pages 16

Breast cancer is the most frequently diagnosed nonskin cancer among women

in the United States and is second only to lung cancer in causing cancer-related

deaths among them (1). The vast majority of deaths are due to recurrent

metastatic disease. Occult dissemination of tumor cells is the main cause of

recurrent metastatic breast cancer (MBC) in patients who have undergone

resection of their primary tumor (2). Approximately 5% of patients with breast

cancer have clinically detectable metastases at the time of initial diagnosis, and

a further 30% to 40% of patients who appear clinically free of metastases

harbor occult metastases (3,4). The formation of metastatic colonies is a

continuous process, commencing early during the growth of the primary tumor.

Metastasis occurs through a cascade of linked sequential steps involving

multiple host-tumor interactions. This complex process requires the cells to

enter the circulation, arrest at the distant vascular bed, extravasate into the

organ interstitium and parenchyma, and proliferate as a secondary colony.

Several experimental studies suggest that during each stage of the process, only

the fittest tumor cells survive (2).