Incidental and nonincidental papillary thyroid microcarcinoma

Subtotal thyroidectomy or lobectomy without radioactive iodide ((131)I) treatment is sufficient for postoperative treatment of incidental papillary thyroid microcarcinoma (PTMC). Aggressive surgical treatment with (131)I therapy is indicated for nonincidental PTMC.

This is a retrospective analysis of 335 PTMC patients who received primary thyroid surgical treatment and long-term follow-up in a single medical center. All PTMC patients were categorized as incidental (group I) or nonincidental (group II). Group II patients (209 cases) were categorized as intrathyroid (group II A), neck lymph node or local regional soft-tissue invasion (group II B) and distant metastasis (group II C) groups.

In group I, 105 of 126 cases received only subtotal thyroidectomy or lobectomy. None died of thyroid cancer. Histological evaluation revealed multicentric PTMC in 12 (9.5%) and 52 (24.9%) cases (P < 0.05) in groups I and II, respectively. In group II, 55 of the 209 patients (26.3%) presented with extrathyroidal involvement. Two cases of relapse occurred in group I and 20 in group II by the end of follow-up. One patient in group II B and two patients in group II C died of thyroid cancer. Nine out of ten patients in group II C were diagnosed with distant metastases before primary thyroid surgical treatment.

Subtotal thyroidectomy is effective surgical treatment for incidental PTMC. For nonincidental cases, aggressive treatment is essential for reducing the risk of cancer relapse or mortality following surgery.