[Papillary thyroid microcarcinoma. Long-term outcome in 587 cases compared with published data]

Papillary thyroid microcarcinoma (PTMC), a tumor measuring =or<1 cm according to the World Health Organization (WHO) histologic classification, is the most common histologic variant of thyroid cancer. The aim of this study was to evaluate the long-term outcome of surgical treatment for PTMC at a single institution with a view to differentiate therapy options based on risk of progression of disease by comparing our results with those reported in the literature.

The study sample was a total of 587 cases of PTMC treated surgically at our institution between 1990 and 2006. PTMC was an incidental finding (PTMC-I) in 325 (55.4%) cases, diagnosed preoperatively (PTMC-D) at echography and needle-aspiration biopsy in 229 (39%), and occult with metastasis (PTMC-O) in 33 (5.6%). Patients were grouped into two classes (PTMC diameter =or>5 mm or <5 mm) and compared against prognostic factors: sex, age, type of PTMC (PTMC-I, PTMC-D, PTMC-O), extent of surgery, lymph node dissection, lymph node metastasis, iodine-131 (131-I) therapy, state of disease, relapses. These parameters were then compared against tumor size (PTMC diameter =or>5 mm or <5 mm), excluding cases of PTMC-O with metastasis.

Comparison of the two groups divided by tumor size, across the entire sample and after PTMC-O cases were excluded, revealed significant differences in the type of PTMC, frequency of partial thyroidectomy, presence of lymph node metastasis, iodine-131 therapy, life status and recurrence rate.

Published PTMC studies were analyzed for definition of the disease, incidence, therapy, prognosis, and follow-up results and compared with our data. The results of our analysis argue against use of the term ''microcarcinoma'' in the wider sense since the three PTMC categories (PTMC-I, PTMC-D, PTMC-O) present different behaviour patterns. When cases of PTMC-O with clinically manifest metastasis were excluded, none of the patients with PTMC <5 mm in diameter were reoperated for tumor recurrence and all are currently free of disease. In conclusion In PTMC <5 mm in diameter, whether PTMC-I and PTMC-D, and without evidence of lymph node involvement, partial thyroidectomy may be a viable approach to treatment. By contrast, occult PTMC with metastasis is prognostically important and should therefore be treated like tumors =or>5 mm in diameter.