Laboratory Corporation of America, also known as LabCorp, was sent a warning letter in which federal officials accuse the company of illegally marketing a drug test to detect ovarian cancer.

The warning letter, dated Sept. 29, clearly states that marketing OvaSure “is in violation of the law,” as the company “does not have marketing clearance or approval from the FDA,” Steven I. Gutman, director in the office of In Vitro Diagnostic Device Evaluation and Safety with the FDA wrote.

The test, developed by researchers at Yale School of Medicine, was first introduced in June, raising hopes among women and their doctors because it promises to detect ovarian cancer at an early stage, when it is still treatable. OvaSure was tested on 224 blood samples and identified 95 percent of cancers correctly. There was a false positive rate of 6 percent.

However, some outside experts, including the Society of Gynecologic Oncologists, have said the test had not been proved accurate. Therefore, they fear it might cause women to have unnecessary surgeries to remove their ovaries. The Society of Gynecologic Oncologists, particularly, maintains that the test is ineffective and too imprecise to detect ovarian cancer and that additional research is needed before offering it to women.

The FDA expressed the same fear in its letter addressed to LabCorp. The agency determined that the OvaSure test was designed, developed and validated by researchers at Yale University and not that of LabCorp. Instructions for use and performance appear to have been developed by Yale researchers. That’s why OvaSure does not fall in a category that can be sold without prior clearance from the agency, the FDA said. Consequently, LabCorp “must take prompt action to correct these violations.”

Ovarian cancer has few warning signs and 80 percent of cases are not caught early when it is curable. That’s why it is known as “the silent killer.” In the US, more than 21,000 cases of ovarian cancer are diagnosed annually. In 2008, more than 15,000 women will die from the disease, according to American Cancer Society estimates. The five-year survival rate is 92 percent if the cancer is caught before spreading to other parts of the body. When the cancer is discovered in advanced stages, five-year survival drops to 30 percent. Women and their physicians have been looking for a screening test to find early ovarian cancer for decades, and OvaSure seemed to have been the answer.

LabCorp spokesman Eric Lindblom said the company was “disappointed” by the letter, but he also added that “we are currently in discussion with the FDA over the next steps and of course we share the FDA’s determination to assure patients are protected.”

LabCorp shares fell nearly 1.8 percent to close at $60.63 on the New York Stock Exchange.

The warning letter was posted on the FDA Web Site at http://www.fda.gov/foi/warning_letters/s6947c.pdf.