Advances in precision medicine have emerged from a new and growing understanding of the genetic changes that occur within cancer cells. New therapies that can specifically target cancer-driving mutations have improved treatment outcomes in breast, lung, and prostate cancer. The result has been a much more targeted attack of the tumor containing the mutated protein or pathway, and a reduction of side effects on a patient’s normal cells and tissues.
Personalized cancer treatment requires access to tumor samples throughout the treatment cycle so that as cancer changes, so does the approach to therapy. Patients can now benefit from the longitudinal monitoring of mutations that are changing in response to treatment. Until recently, detecting mutations that could benefit from targeted drugs has required sampling cells recovered from diseased tissue.
In practice, this means that treatment decisions are made on a tissue biopsy that is representative of the cancer at one point in time and at one location in the body. Clearly, the advent of targeted therapies is driving a need for access to the genetic material of the tumor. To effectively monitor patients on a longitudinal scale, these samples are needed more often and with greater ease of collection than a traditional solid tumor biopsy can provide.
There is a population of tumor cells circulating in the bloodstream that can address this need for closer monitoring—the circulating tumor cell (CTC). Metastasis, the development of secondary malignant growths at distant sites, arises when an accumulation of genetic errors sufficiently deregulate growth control causing the cancer cells to become mobile. These cells, carrying genetic material that reflects the tumor, migrate from their primary site through the bloodstream or the lymphatic system to other, distant sites in the body.