A more sensitive screening test may one day help doctors determine how far colorectal cancer has spread, giving patients a better shot at survival, U.S. researchers said on Tuesday.

They said a genetic test that looks for a specific cancer biomarker known as guanylyl cyclase 2 C found hidden cancer in lymph nodes that had been missed by current screening methods.

Colorectal cancer is the fourth most common cancer in men and the third in women worldwide, striking 1.2 million people each year, according to the American Cancer Society.

"One of the unmet needs of colorectal cancer is an accurate staging method to determine how far the disease has spread," said Dr. Scott Waldman of Thomas Jefferson University in Philadelphia, whose study appears in the Journal of the American Medical Association.

Waldman is a scientific adviser to Targeted Diagnostics and Therapeutics Inc in Pennsylvania, which helped fund the study and has a license to make diagnostic tests based on the research.

The current testing method involves looking at a small sample of tissue from lymph nodes. In about 25 percent of patients whose lymph nodes test clean, the cancer comes back.

Waldman and colleagues wanted to see if a test that looks for the protein guanylyl cyclase C, a marker in lymph nodes associated with increased risk of recurrence of colorectal cancer, might do a better job at finding these hidden cancers.

In prior studies, Waldman and others found this protein is present only in the intestinal wall and in colon cancer cells. Therefore finding it in lymph nodes would suggest the cancer has spread.

In the latest study, the researchers evaluated 257 people with colorectal cancer whose biopsies detected no cancer in the lymph nodes closest to where their tumors had been surgically removed.

Using the genetic test, the researchers found the cancer biomarker in 87.5 percent of patients tested. Of these, 20.9 percent had their cancer come back. That compared with only 6.3 percent of those patients whose lymph nodes tested negative for the cancer biomarker.

Waldman said the findings suggest the more sensitive test might help spot cancers missed in biopsies, but larger studies would be needed to tell how effective the test might be.

Waldman was joined in the study by Dr. David Weinberg of Fox Chase Cancer Center in Philadelphia, who owns shares in Targeted Diagnostics.