A new test developed by scientists could help could help save thousands of cancer victims per year.
It is hoped the "fluid biopsy", which tracks malignant cells moving around the body, will help scientists to stop metastasis, the process by which cancers spread.
This is the primary cause of death in nine out of 10 people struck down by the disease.
The Californian researchers say their test more accurately mapped the journey of cells in patients with prostate, breast and pancreatic cancer. It works by attaching fluorescent "tags" to cancer cell proteins, making them glow.
"This is the technology we have been waiting for to solve the problem of resistance to chemotherapy drugs," the Daily Express quoted leading US oncologist Dr Jorge Nieva as saying.
By tracking cancer cells, doctors will be able to better predict which treatments are working.
The study was published in a report in the Institute of Physics journal, Physical Biology.