Prognostic Factors in Papillary Microcarcinoma with Emphasis on Histologic Subtyping: A Clinicopathologic Study of 148 Cases

Background: There continues to be controversy regarding which clinicopathological features confer a higher risk of adverse outcome in papillary microcarcinomas (PMC). The aim of this study was to assess the prognostic value of a meticulous histologic examination in PMC. Method: All papillary thyroid carcinoma <1cm in size without associated larger thyroid carcinomas, identified between 1977 and 2002, were categorized as PMC and subjected to a meticulous histopathologic examination by 2 thyroid pathologists. Results: 148 PMC patients fulfilled the inclusion criteria. Within PMC, young age, male sex, tumor multicentricity, extrathyroidal extension, and infiltrative and larger tumor (0.5cm) correlated with the presence of >1cm metastatic node (MN) or >3 MN at presentation (p<0.05). With a median follow-up of 9.9 years, only 1 (0.7%) of 134 PMC patients died of thyroid carcinomas and 3 (2.2%) had recurrences in the neck. The patient who died had harbored a poorly differentiated carcinoma in his MN. The presence of MN and especially a large MN (>1cm) correlated with worse recurrence-free survival (p=0.005 and p<0.0001, respectively). Except for one, all individuals with clinically adverse outcomes had >1cm MN. Patients whose MNs were predominantly composed of poorly differentiated carcinoma or tall cell variant papillary thyroid carcinoma had a significant shorter recurrence-free survival (p<0.0001). Only 1 of 80 radioactive iodine-naive PMC patients with absent or small MN (1cm) had recurrence with a median follow-up of 9.2 years. Conclusions: (i) The size and histotype of the MN are predictors of outcome in PMC and should be recorded. (ii) The very rare PMC patients who suffer recurrence or even die of disease have usually aggressive histopathologic features at presentation. (iii) PMC patients with nodal disease that is small or absent at presentation are at a very low risk of recurrence and may be spared radioactive iodine therapy.