Improving the prediction of malignancy in cytologically suspicious thyroid nodules.

Background: Fine needle cytology aspirates (FNA) classified as THY4 are a heterogeneous group suspicious for malignancy [papillary thyroid cancer (PTC)], which is confirmed in 50-80% of cases after surgery.

Aim: To better stratify THY4 FNA specimens for the relative risk of malignancy.

Methods: We retrospectively analyzed 78 thyroid nodules classified as THY4 because of the presence of atypical cells, hypercellular trabeculae and/or intranuclear inclusions (ICI), in the absence of papillae. Two subgroups were identified: group 1 (38 nodules), showing ICI with (no.=17) or without (no.=21) trabeculae and cellular atypia, and group 2 (40 nodules), showing trabeculae and atypia but without ICI.

Results: PTC was detected at histology in 56/78 of the patients (71.8%). Malignancy occurred in 36/38 (94.7%) of the patients in group 1 and in 20/40 (50.0%) of the patients in group 2. Therefore, the positive predictive value (PPV) for PTC was 97.3% in the ICI+ specimens (group 1), with a sensitivity of 64.3% and specificity of 95.2%. When only ICI was present, without atypia and trabeculae, the PPV and specificity were similar (95.0 and 95.2%, respectively), but the sensitivity was decreased (48.7%). In specimens without ICI (group 2), the PPV was only 50.0%; however, combined with young age (<40 yr) and male gender, it reached a value similar to that of group1.

Conclusions: In ICI+ specimens compared to ICI-, the risk of PTC is nearly doubled, since PPV increases from 50.0% to 97.3%. This observation suggests that surgery should be considered mandatory in all lesions classified THY4 at FNA, although the relevant difference in terms of cancer risk between ICI- vs ICI+ nodules might be an useful information for both the clinician and the patient.