Thyroid Cancer Identified After Positron Emission Tomography (PET) Shows Aggressive Histopathology

Incidental thyroid nodules with focal uptake on positron emission tomography (PET) have an increased risk for malignancy, with the majority being differentiated thyroid cancer (DTC). It is unclear whether these cancers have more aggressive histopathology compared with DTC diagnosed via other means.

Electronic medical record of two medical centers was queried for the period of 2001-2016 to identify patients who underwent PET imaging for nonthyroid-related indications and who were found to have focal thyroid uptake. Patients who underwent thyroid nodule fine needle aspiration biopsy (FNAB) and subsequent thyroidectomy with a final diagnosis of DTC were further reviewed. A comparison group, matched for age, tumor type, and tumor size, was selected from consecutive patients who underwent surgery for DTC.

Among 35,124 PET scans reviewed, 227 (0.6%) patients were found to have focal thyroid uptake and underwent FNAB: Fourty-seven (21%) were found to have cancer (36 papillary thyroid cancer (PTC), 9 metastases, and 2 lymphoma). Sixty-seven patients proceeded to surgery: Thirty-one with FNAB of PTC and the rest with indeterminate FNAB necessitating diagnostic thyroidectomy. Compared with the control group, the PET PTC patients involved more men (54% versus 26%, P = 0.003), had more advanced tumor stage (P = 0.03), and had increased BRAF mutation on final pathology (78% versus 42%, P = 0.05).

This study demonstrates that DTC detected on PET is most commonly of the papillary type. Despite the small sample size, the results suggest that these PTC may be more aggressive than PTC detected through other means and more frequently harbor BRAF mutations.