[454] Subclassification of “Follicular Lesion of Undetermined Significance” in Thyroid Fine-Needle Aspirates

Howard H Wu, Ashley Inman, Harvey M Cramer. Indiana University School of Medicine, Indianapolis, IN

Background: Follicular lesion of undetermined significance (FLUS) is a category in the Bethesda system for reporting thyroid cytopathology that encompasses a heterogeneous group of lesions that contain cells exhibiting a degree of architectural and/or nuclear atypia that exceeds expected benign changes but is not of sufficient magnitude to justify classification into other categories. It has been suggested that FLUS could be further subclassified into more distinct subtypes each conferring a different magnitude for the risk of malignancy.
Design: We performed a computerized search of our information system and identified all thyroid fine-needle aspiration (FNA) cases carrying a diagnosis of “atypical follicular cells” that had a follow-up lobectomy or thyroidectomy. The FNA cases were re-reviewed and subclassified into four subgroups: FLUS cannot exclude follicular neoplasm (FLUS-FN), FLUS cannot exclude Hürthle cell neoplasm (FLUS-HCN), FLUS cannot exclude papillary carcinoma (FLUS-PTC) and FLUS, not otherwise specified (FLUS-NOS). Based on the follow-up surgical pathology results, the risks of papillary microcarcinoma (PMC), malignancy (not including papillary microcarcinoma) and neoplasm-NOS (including all malignant tumors, PMC and follicular adenoma) were calculated for each of the 4 FLUS subgroups. The data were analyzed using the t-test.
Results: A total of 138 FLUS cases with surgical pathology follow-up were subclassified into 48 cases of FLUS-NOS, 41 cases of FLUS-PTC, 32 cases of FLUS-FN and 17 cases of FLUS-HCN. The risk of PMC was 22% for FLUS-PTC, 18% for FLUS-HCN, 10% for FLUS-NOS, 9% for FLUS-FN and 15% for all FLUS cases. The risk of malignancy was 32% for FLUS-PTC (p < 0.05), 25% for FLUS-FN, 9% for FLUS-NOS, 0% for FLUS-HCN (p < 0.05) and 18% for all FLUS cases. The risk of neoplasm-NOS was 81% for FLUS-FN, 68% for FLUS-PTC, 53% for FLUS-HCN, 44% for FLUS-NOS and 60% for all FLUS cases.
Conclusions: In our study, subclassification enabled us to further divide FLUS cases into high-risk and low-risk groups. The high-risk group includes FLUS-PTC and FLUS-FN with malignancy risks of malignancy of 32% and 25% respectively. FLUS-HCN has a low risk profile with a risk of malignancy that was similar to that of the benign thyroid nodule but with an 18% risk of PMC and 53% risk of neoplasm. After excluding all specific FLUS subtypes, the remaining FLUS-NOS group demonstrates only a 9% risk of malignancy which is well within the 5-15% malignancy risk suggested for FLUS as described in the original Bethesda system.
Category: Cytopathology

Tuesday, March 20, 2012 8:45 AM

Platform Session: Section F, Tuesday Morning


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