By Merritt McKinney
NEW YORK, Feb 25 (Reuters Health) -- False-positive results on a blood
test caused at least 12 women in the US to be incorrectly diagnosed with a rare
form of cancer, according to researchers at Yale and the University of New
Mexico in Albuquerque.
However, the manufacturer of the test notes that it is approved for
detecting pregnancy, not for diagnosing cancer.
To prevent other women from undergoing such unnecessary treatments, all
suspected cases of the cancer, known as choriocarcinoma, should be confirmed
with both a blood test and urine test, researchers report.
Following a positive result on the blood test, the team note that 12 women
aged 22 to 42 underwent a variety of unnecessary treatments, including
chemotherapy, hysterectomies and removal of the ovaries. One 36-year old ended
up in a coma due to complications from chemotherapy (she recovered), and a
23-year old had her uterus and both ovaries removed surgically. None of the
women appear to have had cancer in the first place, according to a report in the
February 26th issue of the international medical journal The Lancet.
"We were astonished that this was happening," one of the study's authors,
Dr. Laurence A. Cole of the University of New Mexico told Reuters Health. While
Cole did not give an estimate of how often false-positive results occur, he said
that he is contacted by physicians with case reports every week.
"No physician should be doing a radical treatment solely on (the basis of)
a laboratory test without first confirming that the test is not being interfered
with," Cole said.
The confusion centers on a hormone called human chorionic gonadotropin
(hCG), which is present in the body in only two situations -- when a woman is
pregnant, or in the presence of a choriocarcinoma, a pregnancy-related cancer.
This cancer may be diagnosed when a woman is not pregnant and tests positive for
hCG on a blood test. The cancer, a malignancy of fetal origin, often can be
successfully treated with chemotherapy After treatment, the woman should test
negative for the hormone.
But that's not what happened to 12 women who tested positive for hCG,
according to the report. Even after the women underwent various treatments for
cancer, including hysterectomy, chemotherapy and several minor and major
procedures, they still tested positive for the hormone. Apparently, the problem
was also compounded when the women underwent numerous computed tomography (CT),
magnetic resonance imaging (MRI) and positron emission tomography (PET) scans,
and doctors thought they detected cancerous lesions.
According to negative urine tests and other screens, the women never had
cancer, according to Cole and his associate, Dr. Sigi Rotmensch, of Yale
University School of Medicine in New Haven, Connecticut. They conclude that the
false-positive results were caused by a type of antibody present in blood, but
not in the urine, of the women, who were evaluated at the hCG Reference Center
at the University of Mexico, a group that helps doctors interpret confusing hCG
test results.
Cole said that about one out of every 30 people has such antibodies, which
do not cause disease. Based on the results, the investigators conclude that
blood and urine tests should be taken at the same time to determine whether a
woman has choriocarcinoma.
In the interview, Cole said that 11 of the 12 false-positive results were
performed using test kits manufactured by Abbott Laboratories Inc. As previously
reported by Reuters, a proposed class action lawsuit alleging that the company's
hCG test kits were flawed was filed against the company by a Seattle law firm in
November of last year.
But in an interview with Reuters Health, Joe Daab, an Abbott spokesman,
stood behind the accuracy and reliability of the company's product, calling the
allegations of the pending litigation "baseless." He pointed out that the hCG
test is approved only for the detection of pregnancy, not the diagnosis of
choriocarcinoma.
"The medical literature and FDA guidance documents make it very clear
there are limitations to that practice," Daab said. Physicians should perform
confirmatory tests before making treatment decisions based on a positive hCG
test, he said.
In an editorial that accompanies the study, Dr. Kenneth Bagshawe of the
Imperial College School of Medicine in London also points out that hCG tests
have only been approved in the United States to for pregnancy testing. He notes
that it is important for physicians to know the limitations of the tests,
especially in "a litigation-conscious world."
