Circulating tumor cells as lung cancer biomarkers

Circulating tumor cells (CTC) were first observed under light microscopy in 1869 by the Australian physician Thomas Ashworth, who found tumor cells with “similar appearances as the primary tumor” in the circulation of a man with metastatic cancer (1). This important discovery identified the haematogenous route as a medium of distant cancer spread. With recent technological advances, scientists are now able to detect, characterize and isolate CTC, providing a valuable handle for studying the biology of tumor metastasis and a potential tool for guiding clinical cancer management.