Papillary thyroid carcinoma and microcarcinoma: is there a need to distinguish the two?

The clinical significance of papillary thyroid microcarcinoma (PTMC) tumors < or =1 cm is widely debated. The objective of this study was to compare conventional papillary thyroid carcinoma (PTC) (tumors >1 cm) to PTMC and assess for differences in tumor characteristics and patient outcome.

A retrospective chart review of patients with PTC or PTMC who were followed for a minimum of 3 years postoperatively and managed at a single academic institute was performed.

Of 202 patients in the study, 66 (32.7%) had PTMC and 136 (67.3%) had conventional PTC. Patient and tumor characteristics including tumor multifocality, extrathyroidal extension, angiolymphatic invasion, and lymph node metastasis were similar between both groups. Twenty-one percent of the PTMC tumors were discovered incidentally. Patients with conventional PTC were significantly more likely to undergo treatment with radioactive iodine therapy compared to PTMC patients (86.4% vs. 66.7%, respectively, p < 0.003). Disease recurrence was observed in 40 patients and was not statistically different between the two groups; 11 (16.7%) in PTMC and 29 (21.3%) in conventional PTC, p = 0.57. Within the PTMC group, tumors of patients that recurred were significantly larger than those who remained disease free (8.1 mm vs. 6.4 mm, p < 0.05). None of the patients with incidental PTMC had disease recurrence. Angiolymphatic invasion was the only significant prognostic indicator of recurrence on multivariate analysis (p < 0.02).

Nonincidental PTMC can have aggressive tumor features and disease recurrence similar to conventional PTC. These tumors should be managed like any other papillary thyroid malignancy.