Afirma Benign Thyroid Nodules Show Similar Growth to Cytologically Benign Nodules During Follow-Up

The Afirma gene expression classifier (GEC) is a molecular diagnostic test that has a high negative predictive value for ruling out malignancy in thyroid nodules with indeterminate cytology. Many patients with a cytologically indeterminate and GEC benign (Cyto-I/GEC-B) nodule undergo monitoring instead of diagnostic surgery, but few data describe their follow-up.

The objective of the study was to determine the sonographic changes and clinical outcomes for patients with Cyto-I/GEC-B nodules compared with patients with cytologically benign (Cyto-B) nodules.

This was a retrospective analysis of consecutive Cyto-I/GEC-B nodules evaluated at Brigham and Women's Hospital compared with Cyto-B nodules.

Nodule growth of 20% or greater in two dimensions or of 50% or greater in volume, change in sonographic features, and rates of repeat fine-needle aspiration, thyroidectomy, and malignancy.

Ninety-five Cyto-I/GEC-B nodules in 90 patients were identified. Five patients underwent primary surgical resection. Of the remaining 90 nodules, 58 (64.4%) had sonographic follow-up available at a median of 13 months (range 4-40 mo). Cyto-I/GEC-B nodules showed similar growth compared with 1224 Cyto-B nodules using either of the following criteria: 20% or greater in two dimensions (8.6% vs 8.3%, P = .80) or 50% or greater in volume (17.2% vs 13.8%, P = .44). Thyroidectomies were more frequent in the Cyto-I/GEC-B group (13.8% vs 0.9%, P < .0001), but cancer was found in only one patient, with no evidence of persistent disease after initial treatment.

Cyto-I/GEC-B nodules demonstrate similar growth to Cyto-B nodules during follow-up. Although Cyto-I/GEC-B nodules were more frequently resected, only one malignancy was found. These data suggest that reassessment of Cyto-I/GEC-B nodules may be performed similarly to those with benign cytology.