Staging and restaging of NET with 18F-DOPA PET/CT

Objectives Neuroendocrine tumours (NET) are rare tumours. The diagnosis of NET is often very difficult and expensive for a multiplicity of clinical manifestations and lack of diagnostic tests.18F-DOPA PET/CT (FDOPA) seems to be a useful diagnostic tool.

Methods 38 patients (18 females and 20 males; mean age 63 yrs, range 17-86) were prospectively studied with FDOPA between April 2011 and September 2012: 26 pts with NET (suspected, staging or restaging) considering increased tumor markers: chromogranin-A, gastrin, CEA, CA 19.9, CA 13.3); 6 pts in staging of pheochromocytoma/paraganglioma (increased plasmatic and urinary metanephrines); 5 pts with medullary thyroid carcinoma (MTC) (2 in staging and 3 in restaging; increased serum calcitonin); 1 pt in follow up of Meckel carcinoma. FDOPA was performed in dual time modality (whole body acquisition 10 and 60 minutes after iv injection of 4 MBq/Kg of 18F-DOPA). FDOPA was compared with CT/ MRI and/or abdominal ultrasound, and it was correlated with tumor markers.

Results FDOPA was considered pathologic in 16/38 (42%) patients, and negative in 22/38 (58%) patients. In 26 patients with NET 9/26 (35%) were positive, and 17/26 (65%) were negative; in 2/6 (33%) patients with pheochromocytoma/paraganglioma were positive and in 4/6 (65%) were negative. All scans in MTC patients were positive (100%), while follow up scan in Meckel carcinoma was negative (100%). FDOPA had an overall sensitivity of 81% [95% confidence interval (CI) 68-94%], a specificity of 90% (95% CI 80-99%), PPV of 87% (95% CI 76-98%) and NPV of 86% (95% CI 75-97%). The diagnostic accuracy was 86% (95% CI 75-97%). In particular MTC FDOPA had a sensitivity of 100% even if the number of patients were limited.

Conclusions Even if FDOPA doesn’t give the NET receptor status information, it provides an accurate diagnosis and (re)staging of some subtypes, such as CMT. In these cases, preliminary data suggest that positive PET scan seems to be related to tumor marker levels.