A blood test that can detect cancer or determine whether a cancer has begun spreading to other parts of the body has moved a little closer to your doctor's office.

Health care giant Johnson & Johnson announced Monday that two of its units will begin working with Boston researchers to bring the test to market. As well, four big U.S. cancer centres will start studies on the blood test this year.

The experimental test looks for stray cancer cells in the blood, which are cancer cells that have detached from a tumour and mean that a cancer has either spread, or is likely to. Left unchecked, these circulating cancer cells can grow into new tumours.

Circulating tumour cells are found at very low levels in the bloodstream and are hard to detect. While there is one test on the market that can spot cancer cells in the blood -- a test called CellSearch, also made by a J&J unit –- that current test can only give a cell count. It doesn't capture whole cells that doctors can then analyze to monitor disease progression and to choose treatments.

"This new technology has the potential to facilitate an easy-to-administer, non-invasive blood test that would allow us to count tumor cells, and to characterize the biology of the cells," said Robert McCormack, head of Technology Innovation and Strategy at Veridex, one of two J&J units -- Veridex and Ortho Biotech Oncology – collaborating on research on the blood test.

"Harnessing the information contained in these cells in an in vitro clinical setting could enable tools to help select treatment and monitor how patients are responding."

This newest test requires just a couple of teaspoons of blood, meaning patients might even be able to skip painful biopsies of cancer tumours.

Not only can the test detect cancer, it can be used to monitor treatment in already diagnosed patients.

The test is so sensitive that doctors can administer a cancer therapy one day and sample the patient's blood the next day to see if the circulating tumour cells are gone.

Ultimately, the test might also be able to go beyond screening for metastatic cancer to actually spotting primary cancer.  That could one day mean that the test could replace uncomfortable cancer screening methods used now, such as mammograms, colonoscopies and PSA tests.

Lung cancer patient Greg Vrettos, 63, has been part of the Massachusetts research. The Durham, N.H. resident says before his cancer diagnosis in 2004, he had to undergo tissue biopsies, which left him with a collapsed lung.

He believes a blood test would be simpler, less invasive method that will help.find cancers earlier.

"If they could detect this sooner, that is huge. In any kind of cancer, the earlier the detection, the survivability is much higher," he told CTV.

Vrettos is now undergoing treatment for his cancer and still goes to Boston every three months for CT scans and the blood test. He says the test helps track cancer cells in his blood and helped his doctor spot a setback that required his treatment to be adjusted.

The test works with a microchip that is covered in tens of thousands of tiny bristle-like posts. The posts are coated with antibodies that bind to tumour cells.

When blood is forced across the chip, the cancer cells will stick to the posts. Stains then make the cells glow so researchers can count and capture them for study.

The test is said to be so sensitive that it can find even just one cancer cell in a billion or more healthy cells, said Mehmet Toner, a Harvard University bioengineer who helped design the test.

Studies of the chip have already been published in the journals Nature, the New England Journal of Medicine and Science Translational Medicine.

The agreement announced Monday will have Veridex and another J&J unit -- Ortho Biotech Oncology –- working together to improve the microchip, including trying a cheaper plastic to make it practical for mass production.

The companies will start a research centre at Massachusetts General Hospital and will have rights to license the test from the hospital, which holds the patents.

Dr. Shana Kelley, a professor in the Departement of Phramaceutical Science at the University of Toronto and an expert on molecular diagnostics, is part of a U of T team that's developing similar microchip technology that could one day help detect the proteins that are unique to specific cancers.

She says the field is seeing lots of promising developments.

"There is a lot of excitement around circulating tumour cells," she told CTV News. "But we don't have enough clinical data to be able to say whether or not we can use these as substitute of biopsies. But by taking them to a variety of [research] sites, they can get that data and there will be more certainty around it."

She added: "The possibility we could take a liquid biopsy, a blood sample, and see the cancer cells there, it might lead to early cancer detection, and that could transform treatment options."

With a report from the Associated Press