QS263. Incidence of Follicular Thyroid Carcinoma: A 17 Year Experience of Pre-Operative Fine Needle Aspiration Classification As Follicular Lesion Versus Follicular Neoplasm

Abstract

Background: Fine needle aspiration (FNA) classification of follicular thyroid nodules remains a challenging problem as the determination of benign from malignant disease is rarely possible. While research efforts search for Methods to pre-operatively classify follicular nodules that harbor malignancy, the decision for operative excision is largely based on clinical concerns, size of the nodule and age of the patient. We chose to re-examine our clinical outcomes based on the cytopathologic classification of follicular nodules at our institution. The purpose of this study was to assess the incidence of follicular carcinoma in thyroid nodules where the FNA diagnosis was follicular lesion versus follicular neoplasm and evaluate the utility of these diagnostic categories in triaging patients to sugery. We hypothesized that an interpretation of follicular neoplasm would carry a higher incidence of follicular carcinoma. Methods: We conducted a retrospective review of all patients with a diagnosis of follicular lesion or follicular neoplasm by FNA treated during the last 17 years at a single institution. Each record was independently reviewed. The diagnosis of follicular lesion was made on FNA when some colloid or variability in nuclei was suggestive of but not diagnostic for an adenomatous process. Follicular neoplasm was diagnosed on FNA when monotonous follicular cells with a paucity of colloid were present for which a follicular adenoma or carcinoma was favored. All cases with a suspicion for papillary thyroid carcinoma were excluded. All cases with a malignant diagnosis on the surgical resection specimen were evaluated for correlation with FNA site of biopsy and pathologic findings. Chi-squared analysis was used to determine significant differences in incidence of follicular carcinoma between follicular lesion and follicular neoplasm groups. A P- value less than 0.05 was considered significant. Results: Overall 614 patients with thyroid nodules underwent 672 FNAs: 518 were diagnosed as follicular lesion and 154 as follicular neoplasm. 356 (58.0%) patients underwent surgical resection composed of 239 (46.1%) of the patients with a preoperative diagnosis of follicular lesion and 117 (75.9%) of the patients with a cytopathologic diagnosis of follicular neoplasm. Follicular carcinoma was present in 16 (6.7%) of the follicular lesion group and 18 (15.4%) of the follicular neoplasm group. Overall, the incidence of malignancy including papillary thyroid carcinoma-follicular variant, papillary thyroid carcinoma and follicular carcinoma was 12.6% (30 of 239) for follicular lesions and 22.2% (26 of 117) for follicular neoplasms by FNA classification. The incidence of follicular carcinoma as well as overall malignancy was significantly higher for the follicular neoplasm group. Conclusions: At our institution, the cytopathologic evaluation by FNA of thyroid follicular nodules and their classification into follicular lesions versus follicular neoplasms serves to identify patients at greater risk for follicular carcinoma. Additionally, other malignancies are identified in a greater proportion of follicular neoplasms. Although malignancy may be present in either follicular neoplasms or follicular lesions, follicular neoplasms represent a higher risk nodule and thus this information is helpful when weighing the risk benefit ratio of surgical excision in a patient with a follicular nodule.