Aggressive papillary thyroid microcarcinoma: prognostic factors and therapeutic strategy

Papillary thyroid carcinomas smaller than 1 cm are classified as papillary microcarcinomas (PMCs). Papillary microcarcinomas are usually considered low-risk tumors; however in some cases, PMCs behave aggressively and metastasize early, giving rise to clinically metastatic disease. Debate exists in the literature about prognostic factors and therapeutic management to PMC. We report here the long-term experience of our referral center for malignant thyroid disease.

We retrospectively analyzed 149 consecutive patients with PMC who underwent surgery at our institution between 2000 and 2005; 49 of them (33% of cases) were treated also with radioiodine therapy. Clinical and histopathological parameters potentially predicting patient outcome and recurrent disease were statistically investigated, after a minimum follow-up of 5 years.

After a median follow-up of 5.4 years (range, 5-11 years), 28 (19%) of 149 patients experienced recurrent disease. All of them were reoperated on and newly treated with radioiodine administration. Of these 28 patients, 27 are living without disease, whereas 1 patient died due to metastatic thyroid cancer to lungs. The multivariate statistical analysis identified extrathyroid 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 independent risk factors for the appearance of PMC recurrences. Of note, in most patients who experienced recurrent disease, the PMC had been diagnosed preoperatively and often for the presence of cervical clinically evident lymphadenopathy. On the other hand, none of the PMC "incidentally" discovered at histopathological examination alone experienced recurrent disease during follow-up.

Although most PMCs have an indolent course, there is a fraction (19% in our series) of patients with PMC and aggressive behavior strongly correlated with some histopathological features (extrathyroid invasion, solid pattern, tumor multifocality, and absence of a capsule) who need to be individualized and for whom a radical therapeutic approach is recommended based on total thyroidectomy and lymphadenectomy followed by radioiodine administration.