Micromedullary Thyroid Cancer: How Micro Is Truly Micro?

The aggressive nature of medullary thyroid cancer (MTC) is evidenced by its propensity to present early with lymph node (LN) metastases. The clinical significance of sporadic MTC ≤1 cm (micro-MTC) is not clearly defined.

We performed a retrospective review of the clinical, laboratory, and pathologic data for all patients treated or followed at our institution for sporadic micro-MTC from 1987 through 2008.

A total of 18 patients met the criteria for inclusion in our study. All tumors were unifocal and C-cell hyperplasia distant from the tumors was uniformly absent. Fourteen (78%) patients underwent total thyroidectomy, and the remaining four (22%) patients with tumors ≤0.5 cm had lobectomy with isthmusectomy alone. Four (22%) patients were found to have LN metastases. However, none of the nine patients with tumors <0.5 cm had clinical evidence of LN metastases. Patients were followed for a median of 3.3 (mean, 4.5) years, and there were no deaths. Postoperative calcitonin levels were available for all patients, of whom 14 had normal levels (range, 0–3.9 pg/ml). The four patients with elevated postoperative calcitonin levels (range, 6.3–644 pg/ml) had tumors ranging from 0.7–0.9 cm in size.

Tumors <0.5 cm were associated with a complete absence of clinically detectable nodal disease or elevated postoperative calcitonin levels. The complete absence of multifocal or bilateral disease argues against the need for completion thyroidectomy for sporadic micro-MTC.