A therapeutic strategy for incidentally detected papillary microcarcinoma of the thyroid.

Papillary microcarcinoma of the thyroid (PMCT) is defined as papillary carcinoma measuring 1.0 cm or less. PCMT are frequently detected by ultrasonographic screening and ultrasonography-guided fine-needle aspiration biopsy. Although PMCT can pathologically show a high incidence of multifocality and lymph node metastasis in surgical specimens, most tumors grow slowly or not at all when they are monitored without surgery. In our observations only 6.7% of PMCT enlarged by 3.0 mm or more in diameter during 5 years of follow-up, and nodal metastases became detectable in 1.7% of patients overall. Observation without surgery could, therefore, be an attractive alternative for patients with low-risk PMCT; however, occult PMCT, which are diagnosed as the origin of lymph node or distant metastasis, show a worse prognosis. Even among incidentally detected PMCT, tumors with ultrasonographically detectable nodal metastasis are more likely to recur. Because such PMCT are most likely to recur in the regional lymph nodes, careful therapeutic neck dissection and total thyroidectomy are required. For incidentally detected and low-risk PMCT, careful observation without surgery might be acceptable, but careful and systematic surgery should be performed for patients with PMCT demonstrating aggressive characteristics.