Improving the prediction of malignancy in cytologically suspicious thyroid nodules

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.

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

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.

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.

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.