18.  Screening for Thyroid Cancer

RECOMMENDATION

Routine screening for thyroid cancer using neck palpation or

ultrasonography is not recommended for asymptomatic children or adults.

There is insufficient evidence to recommend for or against screening

persons with a history of external head and neck irradiation in infancy or

childhood, but recommendations for such screening may be made on other

grounds (see Clinical Intervention).

Burden of Suffering

Thyroid cancer accounts for an estimated 14,000 new cancer cases and

more than 1,000 deaths in the U.S. each year.1 The annual incidence is

about 4/100,000 population.2 Women account for 77% of new cases and

61% of deaths.1 Current overall 5-year survival with treatment is 95% in

whites and 90% in blacks,1 but is much lower with some histologic types

(e.g., medullary, anaplastic).3-5 Among those at substantially increased

risk for thyroid cancer are persons exposed to external upper body

(especially head and neck) irradiation during infancy or childhood, and

individuals with a family history of thyroid cancer or multiple endocrine

neoplasia type 2 (MEN 2) syndrome.6-10 The risk of radiation-induced

thyroid nodularity and cancer increases with radiation dose and decreases

with increasing age at which irradiation occurred.7-12 In several large

cohort studies, the absolute excess risk of thyroid cancer associated with

low-dose irradiation given before 18 years of age ranged from 0.3 to

12.5/10,000 person-years per Gy (Gy = radiation dose).8-10 Medullary

thyroid cancer, which comprises about 10% of all thyroid malignancies, is

inherited in one fourth of cases as part of the autosomal dominant MEN 2

syndrome.6,13

Accuracy of Screening Tests

Common screening tests for thyroid cancer include neck palpation and

ultrasonography to detect nodules. Screening for medullary thyroid cancer

as part of the autosomal dominant syndrome MEN 2 is performed at

specialized centers13a rather than by primary care providers and will not

be considered further in this chapter. Diagnostic procedures such as

scintigraphy and fine-needle aspiration with cytology are generally

reserved for persons with evidence of nodular disease or goiter. 

The accuracy of neck palpation as a screening test varies with the

examiner's technical skill and the size of the mass.14 Among

asymptomatic persons, palpation had a reported sensitivity of 38% for any

thyroid disease (compared to examination at surgery for

hyperparathyroidism), and 4 of 6 thyroid tumors were missed by

palpation.15 Compared to ultrasonographic examination, the sensitivity of

neck palpation for detection of solitary thyroid nodules was only 15%,

although no nodules were malignant.16 Of 821 patients with no history of

thyroid abnormalities and without clinically palpable nodules at autopsy,

100 had solitary nodules on macroscopic inspection of serially sectioned

glands, and 17 had primary thyroid cancer.17 Direct palpation of the

excised thyroid gland at autopsy had a sensitivity for solitary nodules of

only 24% compared to macroscopic inspection. These studies suggest a

negative examination does not appreciably decrease the probability of

thyroid nodules or cancer.

Neck palpation for thyroid nodularity has a high specificity in

asymptomatic persons (93-100%), but routine palpation for thyroid

nodules as a screening test to detect thyroid cancer generates many

false-positive results because only a small proportion of nodular thyroid

glands are neoplastic.14,17,18 Periodic screening by palpation of almost

77,000 Japanese women detected thyroid cancer in 0.14%; the likelihood

of thyroid cancer in the presence of a palpable thyroid abnormality was

6%.18 A similarly high false-positive rate has been reported when

ultrasonography is used as a screening test for thyroid abnormalities. In

Finnish studies, ultrasound screening of 354 asymptomatic persons

detected 56 solitary nodules, but none was malignant on biopsy.16,19

Those falsely identified as positive by screening tests must undergo the

inconvenience, expense, and anxiety of needless additional testing,

including invasive tests such as biopsy, to rule out cancer.

Persons exposed to upper body irradiation in childhood have a higher

prevalence of thyroid cancer, but also have a higher prevalence of thyroid

nodularity.8-11 It is unclear what effect a history of irradiation has on

the likelihood of thyroid cancer in the presence of palpable thyroid

nodularity. Periodic screening by neck palpation of 1,500 patients with a

history of thyroid irradiation detected carcinoma in 1%.20 The likelihood

of thyroid cancer given detection of any nodular disease was only 3%, but

the likelihood of malignancy among patients with nodular disease that

was suspicious for cancer (e.g., solitary nodules) was not reported. Only

17% of the patients with nodularity actually underwent surgery, of whom

20% had thyroid cancer.

Effectiveness of Early Detection

The benefits of early detection of thyroid cancer in the general population

are not well defined. For all histologic types, 5-year survival is

significantly better with earlier stage at diagnosis.3 A cohort study of

mass screening found a significantly higher 7-year cumulative survival

rate in patients whose cancer was detected by screening (98%) when

compared with those presenting with symptoms (90%).18 Cancers

detected by screening were significantly more likely to have a favorable

histology, however, and both lead-time and length biases are likely in this

study. There have been no controlled trials demonstrating that

asymptomatic persons detected by screening have a better outcome than

those who present with clinical symptoms or signs. In addition, not all

cancers detected through screening are likely to present clinically during

the patient's lifetime. In autopsy studies in the U.S., the prevalence of

occult thyroid carcinoma in adults ranges from 2-13%;17,21,22 in

contrast, the annual incidence of thyroid carcinoma is only about

4/100,000 population.2

Recommendations of Other Groups

The American Cancer Society recommends screening for thyroid cancer by

palpation every 3 years in persons aged 21-40 years and annually in those

more than 40 years old.23 The American Academy of Family Physicians

recommends palpation for thyroid nodules in adults with a history of

upper body irradiation;24 this recommendation is currently under review.

The Canadian Task Force on the Periodic Health Examination concluded

that there was poor evidence for either inclusion or exclusion of screening

for thyroid cancer in the periodic health examination.25

Discussion

Given the lack of evidence that early detection of thyroid cancer by

screening improves outcome, the high prevalence and uncertain clinical

significance of occult throid carcinoma, the poor sensitivity of neck

palpation in the detection of thyroid nodules, the fact that most positive

screening tests would be false-positives, and the invasive nature of

diagnostic tests (e.g., biopsy) likely to follow a positive screening test,

routine screening for thyroid cancer cannot be recommended at this time.

For persons irradiated in childhood, the greater likelihood of having both

thyroid nodules and malignancy means that the yield from screening is

likely to be higher. The clinical benefits of such screening have not been

established, however.

CLINICAL INTERVENTION

Screening asymptomatic adults or children for thyroid cancer using either

neck palpation or ultrasonography is not recommended ("D"

recommendation). Although there is insufficient evidence to recommend

for or against such screening in asymptomatic persons with a history of

external upper body (primarily head and neck) irradiation in infancy or

childhood, recommendations for periodic palpation of the thyroid gland in

such persons may be made on other grounds, including patient preference

or anxiety regarding their increased risk of cancer ("C" recommendation).

The draft update of this chapter was prepared for the U.S. Preventive

Services Task Force by Carolyn DiGuiseppi, MD, MPH.

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