MULTIFOCALITY
IN PAPILLARY THYROID MICROCARCINOMA – CLINICAL CONSIDERATIONS
Papillary
thyroid microcarcinoma (PTMC) is defined as papillary thyroid cancer being 10
mm or less in the larger dimension. PTMC is commonly diagnosed today, due to
the widespread use of high-resolution ultrasonography for the investigation of
neck diseases, including carotid stenosis. Multifocality and bilaterality are
common features in PTMC; indeed, PTMC is multifocal in a very significant
percentage of cases, ranging from 20 % to 87 %. Multifocality is a feature which is strongly associated
with bilaterality. Multifocality may represent intrathyroidal metastases from a
single cancer cell clone or may develop from multiple independent origins. The
latter hypothesis has been investigated using modern molecular techniques,
which confirmed that multifocal PTMC are most commonly multiple synchronous primary
tumors arising from autonomous clones. Multifocality is a histopathological feature
that is typically evaluation after surgical resection.
Preoperative
diagnosis of multifocality may be difficult by presurgical evaluation using currently
available diagnostic methodology (ultrasonography and fine-needle aspiration
cytology) and thus partial thyroidectomy in patients with bilateral PTMC may
lead to the necessity for reoperation.
Despite
some controversy, multifocality / bilaterality is generally regarded as a risk
factor for lymph node metastases in the central compartment of the neck (level
VI), especially in the presence of more than 3 tumor foci, and this may
indicate higher tumor aggressiveness and a higher risk of regional recurrence.
In the absence
of other adverse features and according to the American Thyroid Association,
radioiodine ablation therapy (RIA) is not routinely recommended after
thyroidectomy for patients with multifocal PTMC; however, consideration of
specific features of the individual patient that could modulate recurrence risk
(such as lymph node metastases, invasion of thyroid capsule, extrathyroidal extension
etc.), disease follow-up implications, and patient preferences are important to
RIA decision-making.
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