Papillary thyroid carcinoma: metastases and microcarcinoma
THE CONTEXT
Papillary thyroid carcinoma (PTC)* is the most common thyroid malignancy. Many small lesions remain undetected or have little clinical impact.
Frequency and metastatic behaviour
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Autopsy studies identify PTC deposits in up to 30% of patients dying of non-thyroid disease, suggesting that many people live with undetected disease.
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Most patients are offered treatment when PTC is diagnosed.
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PTC has a propensity for lymph node metastases. These are more common in younger patients but do not affect their otherwise excellent survival.
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Occult central neck micrometastases may be present in as many as 40% of N0 patients. Few progress to clinically meaningful disease, so the role of elective nodal surgery is questioned.
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Distant metastases are uncommon.
Papillary microcarcinoma
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Papillary microcarcinoma is PTC measuring less than 10 mm.
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These lesions are found in about 10% of benign thyroid resections and are not associated with adverse outcomes, including recurrence or non-survival.
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Management and follow-up are controversial because these lesions may have doubtful clinical significance.
Approaches to small lesions
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National screening in Korea has substantially increased detection of papillary microcarcinoma.
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Japanese groups using observation without surgery have reported that at least two-thirds of lesions never progress.
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Some groups in the USA are attempting nonsurgical ablation with ethanol or radiofrequency.
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In much of the world, groups limit biopsies to lesions larger than 10 mm to avoid diagnosing small lesions of little significance and manage diagnosed lesions conservatively.