Papillary thyroid microcarcinoma: proposal of treatment based on histological prognostic factors evaluation

Abstract

Background: Papillary thyroid cancer accounts for approximately 80% of thyroid tumors and its incidence has increased over the past decades. Papillary thyroid microcarcinomas (PMCs), defined by the World Health Organization as less than 1.0 cm in size, are identified with greater frequency. The majority of patients with PMCs follows a benign clinical course, however a subgroup of these carcinomas is as aggressive as bigger tumors. Risk factors related with poor outcome have not been defined and the optimal treatment has not been proved. The authors investigated histologic prognostic factors predicting high risk patients considered for more aggressive treatment and propose reviewed therapeutic guidelines based on analysis of histopathologic features which determined the recurrence rate.

Study design: One hundred forty nine patients with PMC who underwent surgery were retrospectively analyzed. Clinical and histopathologic parameters potentially predicting patient outcome and recurrent disease were statistically investigated, after a minimum follow-up of 5 years.

Results: After a median follow-up of 5.4 years 28 of 149 patients experienced recurrent disease. All of them were reoperated on and newly treated with radioiodine administration. The multivariate statistical analysis identified extrathyroidal invasion (Odds Ratio, OR, 58.54; P=0.013), the solid pattern (OR,25.77; P>0.001), the tumor multifocality (OR, 15.80; P= 0.005), and the absence of tumor capsule (OR, 9.74; P=0.015) as significant and indipendent risk factors for the appearance of PMCs recurrences. Of note, none of the PMC "incidentally" discovered at histopathological examination alone experienced recurrent disease during follow-up.

Conclusions: Although most PMC have favourable long-term prognosis, some patients (19% in our series) presented aggressive clinical course strongly correlated with some histopathologic features (extrathyroidal invasion, tumor multifocality, solid pattern and absence of capsule) who need to be investigated and for whom a radical therapeutic approach is recommended based on total thyroidectomy and regional lymphadenectomy followed by radioiodine administration.