[ RadSafe ] Article: 'Rise' in thyroid cancers comes from better detection methods
crispy_bird at yahoo.com
Tue Jun 20 11:56:27 CDT 2006
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Diagnostic Imaging Online
June 14, 2006
'Rise' in thyroid cancers comes from better detection
More sophisticated detection methods account for a
dramatic increase in thyroid cancer over the last 30
years, rather than a true change in occurrence of the
disease, according to a study in the Journal of the
American Medical Association. Physician self-referral
may also be a contributing factor.
Radiation is a common cause of thyroid cancer, and
some have questioned whether the increase in thyroid
cancer incidence was linked to greater exposure to
radiation in the environment.
But stable mortality rates despite the apparent rise
in incidence led researchers to conclude that the
increase is actually due to better detection, not
greater occurrence of disease.
Dr. Louise Davies and Dr. H. Gilbert Welch of the VA
Outcomes Group and Dartmouth Medical Center
investigated causes behind the increase of thyroid
cancer incidence from 3.6 per 100,000 in 1973 to 8.7
per 100,000 in 2002 (JAMA 2006;295:2164-2167).
The 2.4-fold increase is mostly due to the detection
of subclinical papillary cancers 2 cm or smaller.
During the 30-year span, the incidence of papillary
cancers grew from 2.7 to 7.7 per 100 000, a 2.9-fold
The researchers found no significant change in
incidence of the less common histological types:
follicular, medullary, and anaplastic. In 2002, for
example, papillary cancers accounted for 88% of all
thyroid cancers, while 9% were follicular, and 3% were
either medullary or anaplastic.
"Given the known prevalence of small asymptomatic
papillary thyroid cancers at autopsy, we believe this
suggests that increased diagnostic scrutiny has caused
an apparent increase in incidence of cancer rather
than a real increase," the authors said.
The use of ultrasound for thyroid disease became
widespread in the 1980s, while fine-needle aspiration
flourished in the 1990s. Ultrasound can detect nodules
as small as 0.2 cm. FNA, which can be performed
quickly during an office visit, replaced lengthy
nuclear medicine scans.
"The ability to detect small nodules and then aspirate
their contents has clearly facilitated the diagnosis
of these smaller cancers," the authors said.
In fact, overdiagnosis of the disease has itself
become a concern. While many people may die with
papillary nodules, they do not die from them. Yet 75%
of those with papillary cancers less than 1 cm undergo
total thyroidectomy. This procedure carries small but
significant risks of complications and requires
lifetime maintenance and surveillance.
This concern is growing as thyroid ultrasound moves
from the radiology department to physicians' offices.
When ultrasound is used as an office-based adjunct to
physical examination, the likelihood of self-referral
increases, along with the number of nodules -- and,
ultimately, cancers -- found and treated.
The authors suggest that follow-up for symptomatic
thyroid nodules may be an appropriate course and that
papillary cancers smaller than 1 cm could be
classified as a normal finding.
They conclude that further research is needed to
determine appropriate management of small papillary
cancers detected with ultrasound and fine-needle
aspiration. Data for the study came from Surveillance
Epidemiology and End Results (SEER) and the National
Vital Statistics System.
For more information from the Diagnostic Imaging
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-- By Emily Hayes
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