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Thyroglobulin level detection, even when there is no sign of a
tumor, was correlated with a recurrence of cancer within three to five years in
about 80 percent of patients.
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COLUMBUS , Ohio ? A blood test for thyroid cancer can
detect persistent or recurrent disease even before doctors
can find any trace of a tumor, according to a new study. The
findings suggest that people treated for the disease should
be examined regularly for early signs of recurrence.
The study, by researchers at The Ohio State University
Comprehensive Cancer Center ? Arthur G. James Cancer Hospital and
Richard J. Solove Research Institute (OSU CCC ? James), examined how
well a test for thyroid cancer can predict whether the disease will
recur.
The findings were published June 21 online in the Journal of
Clinical Endocrinology & Metabolism.
The test measures a protein known as thyroglobulin (Tg),
which is made by thyroid-cancer cells. The measurement is taken
after a person is injected with a relatively new drug known as
thyrotropin alfa, or Thyrogen. The drug allows Tg testing without
the sometimes debilitating side effects of hypothyroidism that
otherwise accompany the test when stimulation testing is done.
"We were surprised to find that even with relatively low
thyroglobulin levels, and even when there is no sign of a tumor,
about 80 percent of patients had a recurrence of their cancer within
three to five years," says first author Richard T. Kloos, associate
professor of internal medicine and of radiology.
"This indicates that we are detecting these tumors very early,
and that time and diligence may be needed to find them."
The study also found that even when Tg levels are very low or
undetectable, about 2 to 5 percent of patients still have a
recurrence after three to five years.
"Currently, some thyroid-cancer treatment guidelines say that
these patients may never need further testing, but our data
contradict that," says Kloos, co-director of the Thyroid Cancer Unit
at the OSU CCC ? James.
Thyroid cancer is usually treated surgically by removing the
thyroid gland, followed by drinking radioactive iodine to kill any
remaining cancer cells. Patients must then take synthetic thyroid
hormone for life.
With all thyroid cells eliminated, the Tg level should be zero,
and its presence later signals a possible return of the disease.
(Sometimes, however, low levels of Tg can be present following
treatment, and slowly decline over time.)
In the past, Tg testing required that patients stop taking their
synthetic thyroid hormone several weeks before the test.
"That worked fairly well, except that some people became
miserable after they stopped taking their synthetic thyroid hormone
and became hypothyroid," Kloos says. "Some patients claimed that
they'd rather die of their disease than go through that regularly."
Withdrawing from thyroid hormone can cause fatigue, weight gain,
constipation, mental dullness, lethargy, depression and other
symptoms. Thyrogen, approved for use in 1998, allowed people to have
a stimulated Tg test and continue taking the synthetic hormone.
The present study sought to help interpret the results of the
Thyrogen-assisted Tg test. It involved 107 patients (88 women and 19
men; average age 36 years) treated for papillary, follicular or
Hurthle cell thyroid cancer. Following surgery and radioactive
iodine treatment, the patients were injected with Thyrogen and
tested for Tg levels between January 1999 and March 2001.
The patients were divided into three groups based on their Tg
reading. Group 1 patients had Tg levels below 0.5, group 2 had Tg
levels of 0.6 to 2.0, and Group 3 had Tg levels greater than 2.0.
(The numbers represent nanograms of Tg per milliliter of blood
serum.)
After three to five years, the researchers found recurrent tumors
in about 80 percent of the patients with Tg levels above 2.0, and in
about 2 percent of those with Tg levels below 0.5.
An estimated 25,690 new cases of thyroid cancer are expected in
2005, with 19,190 of those expected to occur in women; 1,490 people
are expected to die of the disease. In addition, about 330,000
living Americans have been treated for thyroid cancer, about 20
percent of whom are likely to have a recurrence.
###
Ernest L. Mazzaferri, OSU emeritus professor and chairman of
medicine, was a co-author of the study.
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