Papillary microcarcinoma of the thyroid-Prognostic significance of lymph node metastasis and multifocality

Background: It is known that patients with papillary microcarcinoma (PMC) of the thyroid gland have a very favorable prognosis. The rising incidence of PMC among papillary thyroid carcinoma (PTC) necessitates the identification of prognostic factors and the formulation of treatment protocols.

Methods: The authors conducted a retrospective analysis of 203 patients with PMC who were diagnosed on or before 1999 and were treated at the Department of Clinical Oncology, Queen Elizabeth Hospital, Hong Kong.

Results: The cause specific survival, locoregional (LR) failure free survival, and distant metastases failure free survival rates at 10 years were 100%, 92.1%, and 97.1%, respectively. Five patients had lung metastases; 2 patients died of their metastases 12.9 years and 14.8 years after diagnosis, and 3 patients achieved clinical remission after radioiodine (RAI) treatment. Twelve patients had LR recurrences. Patients with LR recurrence were highly salvageable with a combination of surgery, RAI treatment, and external radiotherapy; all but one (who refused treatment) were alive without disease at last follow-up. Multivariate analyses did not reveal any independent prognostic factor for survival. The risk of cervical lymph node (LN) recurrence increased 6.2-fold (P = 0.01) and 5.6-fold (P = 0.02) when LN metastases and multifocal disease were present at diagnosis. RAI ablation reduced the LN recurrence rate to 0.27 (P = 0.04). The presence of LN metastasis increased the rate of distant metastasis 11.2-fold (P = 0.03). Age was not a significant factor in predicting disease recurrence or survival. Subdivision by tumor sizes </= 5 mm and > 5 mm did not affect the outcome, but no patient with tumors <or= 5 mm had mortality related to PMC.

Conclusions: Despite the overall excellent prognosis for patients with PMC, PMC was associated with a 1.0% disease-related mortality rate, a 5.0% LN recurrence rate, and a 2.5% distant metastasis rate. Therefore, the treatment of patients with PMC should be no different from the treatment of patients with conventional PTC: i.e., complete surgery with consideration for RAI and/or external radiation therapy if poor prognostic factors are present.