Papillary thyroid microcarcinoma: a study of 535 cases observed in a 50-year period

The study aims were to characterize patients with papillary thyroid microcarcinoma and to provide data on outcome after surgical therapy.

Five hundred thirty-five patients with papillary microcarcinoma had initial treatment at Mayo Clinic from 1940 to 1989. Follow-up extended to 48 years. Median follow-up time for 400 survivors was 16 years. Recurrence and mortality details were derived from a computerized cancer database.

Median tumor size was 8 mm. Ninety-nine percent of tumors were histologic grade 1; 98% were not locally invasive. Thirty-two percent of patients had nodal metastases at examination. TNM stages were I in 485 patients (91%), III in 49 patients (9%), and IV in one patient (0.2%). Ninety-one percent of patients underwent bilateral lobar resection. Tumor resection was incomplete in three cases (0.6%). Radioiodine remnant ablation was performed in 55 patients (10%). All-causes survival did not differ from expected; two patients (0.4%) died of papillary microcarcinoma. Twenty-year tumor recurrence rate was 6%. Higher recurrence rates were seen either with node-positive patients (p < 0.0001) or after unilateral lobectomy (p < 0.0001). Recurrence rates did not appear to be significantly altered by total thyroidectomy (p = 0.44) or radioiodine remnant ablation in node-positive patients (p = 0.99).

These results reaffirm that papillary microcarcinoma has an excellent prognosis if managed initially by bilateral lobar resection. Routine radioiodine remnant ablation is not indicated.