The Food and Drug Administration warned Burlington-based Laboratory Corporation of America Holdings that it is breaking the law by selling a blood test for ovarian cancer without the agency’s approval, the FDA wrote on its Web site.

Written by Steven I. Gutman, director in the office of In Vitro Diagnostic Device Evaluation and Safety, and addressed to LabCorp president and CEO David P. King, the letter says the U.S. independent clinical laboratory company violates the law by marketing OvaSure since “you do not have marketing clearance or approval from the FDA.”

OvaSure is a blood test that assesses the level of six proteins in a woman’s blood and estimates the probability that she has ovarian cancer. It is able to detect this type of cancer in early stages, when it is still confined to the ovaries.

The need for this blood screening method is unbelievably great. Ovarian cancer is the fifth main cause of death from cancer in women and the main cause of death from gynecological cancer. According to the American Cancer Society, over 90% of women suffering from this type of cancer will prolong their lives with at least five years if it is detected at its earliest stage, when it can be still treated.

More than 200 women participated in an OvaSure trial. Some of them were diagnosed with ovarian cancer but others were healthy. The results showed that both the accuracy of a positive prediction and the accuracy of a negative prediction were at the same level of 95 percent.

LabCorp didn’t say if OvaSure, which costs about US$220 to US$240, will be removed from the market. “While we are disappointed in the letter ... we share the FDA’s interest in avoiding unnecessary regulatory burdens in diagnostic testing and in ensuring safety for patients,” Eric Lindblom, a spokesman for the clinical laboratory company, wrote in an e-mail message.