What is the biology and optimal treatment for papillary microcarcinoma of the thyroid?

BACKGROUND: Papillary microcarcinomas of the thyroid, defined as tumors measuring < or =10 mm, are believed to be a less aggressive subset of papillary cancers that behave more like benign lesions and are often more conservatively treated. However, some groups have reported a high incidence of metastases from papillary microcarcinomas and favor aggressive surgical resection followed by radioiodine therapy. Therefore, to characterize the biology and optimal treatment for papillary microcarcinomas, we reviewed our experience.
METHODS: From May 1994 to October 2004, 184 patients underwent thyroid surgery at the University of Wisconsin and had papillary thyroid cancer present in the resected gland. Of these patients, 10 were excluded because there was no record of tumor size. Of the remaining 174 patients, 74 (42%) had papillary microcarcinomas. Data from these patients were retrospectively analyzed.
RESULTS: The mean age of these patients was 42 +/- 1.48 year and 57 (77%) were female. The mean tumor size was 5.7 +/- 0.38 mm. Of the 74 patients, 12 (16%) had lymph node metastases. The majority of patients (65%) underwent a total thyroidectomy and 61% had radioiodine ablation therapy after surgery. With follow-up up to 134 months, the recurrence rate was 8% and only two patients currently have active disease. No patients with papillary microcarcinoma have died during this period.
CONCLUSION: Papillary microcarcinomas of the thyroid are quite common, comprising almost half of all papillary cancers. Despite a significant rate of metastatic disease, the prognosis for patients with microcarcinomas has been excellent with 100% survival and a low recurrence rate. These outcomes may be the result of the aggressive surgical therapy used at our institution. Thus, papillary microcarcinomas appear to have a similar biology to other low risk papillary thyroid cancers and, in our opinion, may warrant similar treatment.