Diagnostic value of [¹⁸F]Fluorocholine PET/CT in detection of primary medullary thyroid cancer

Objective

Medullary thyroid cancer (MTC) is a challenging neuroendocrine malignancy where the role of nuclear medicine imaging is currently limited. This paper investigates the potential diagnostic value of [¹⁸F]Fluorocholine PET/CT in primary MTC.

Methods

We prospectively enrolled 25 patients (10 male, 15 female) with suspicion for primary MTC based on fine-needle aspiration biopsy (FNAB). All patients had a baseline three phase [¹⁸F]Fluorocholine PET/CT (2.5 MBq/kg): two regional head and neck and upper mediastinum studies at 5 min (first phase) and 120 min (third phase) and a whole-body PET/CT (from the skull vertex to mid-thighs) at 60 min (second phase). Any non-physiological radiotracer uptake was regarded as MTC positive. All patients referred to surgery had a preoperative neck-US. True lesion status was assessed using either histopathology, FNAB results or follow-up imaging and laboratory (calcitonin, CEA) results. Results with p < 0.05 were considered statistically significant.

Results

Nineteen of 25 patients (76%) were surgically treated and histopathology reports were obtained. Patient-based sensitivity and positive predictive value for detection of any MTC lesion using [¹⁸F]Fluorocholine PET/CT were both 100%. Neck-US was more specific (100% vs 70%; p = 0.002) and had a higher positive predictive value than [¹⁸F]Fluorocholine PET/CT (100% vs 55%; p = 0.018) for N1a and N1b staging. [¹⁸F]Fluorocholine PET/CT had a higher sensitivity (100% vs 50%; p = 0.025) and higher negative predictive value (100% vs 81%; p = 0.026) than neck-US for N1b staging. The optimal SUV_max cut-off to differentiate malignant from benign neck lesions at 60 and 120 min was 2.56. Patients with M1 stage on PET/CT had higher calcitonin (median of 5,372 vs 496.6 pg/ml; p = 0.005) and CEA concentrations (median of 95.8 vs 18.65 µg/l; p = 0.034) compared to patients with M0 disease.

Conclusion

[¹⁸F]Fluorocholine PET/CT appears to be a promising radiotracer for primary staging of MTC by increasing diagnostic accuracy for N staging and detecting possible distant metastatic sites at initial presentation of disease.