Total ¹⁸F-dopa PET tumour uptake reflects metabolic endocrine tumour activity in patients with a carcinoid tumour

Abstract

Purpose

Positron emission tomography (PET) using 6-[ ¹⁸F]fluoro- L-dihydroxyphenylalanine ( ¹⁸F-dopa) has an excellent sensitivity to detect carcinoid tumour lesions. ¹⁸F-dopa tumour uptake and the levels of biochemical tumour markers are mediated by tumour endocrine metabolic activity. We evaluated whether total ¹⁸F-dopa tumour uptake on PET, defined as whole-body metabolic tumour burden (WBMTB), reflects tumour load per patient, as measured with tumour markers.

Methods

Seventy-seven consecutive carcinoid patients who underwent an ¹⁸F-dopa PET scan in two previously published studies were analysed. For all tumour lesions mean standardised uptake values (SUVs) at 40% of the maximal SUV and tumour volume on ¹⁸F-dopa PET were determined and multiplied to calculate a metabolic burden per lesion. WBMTB was the sum of the metabolic burden of all individual lesions per patient. The 24-h urinary serotonin, urine and plasma 5-hydroxindoleacetic acid (5-HIAA), catecholamines (nor)epinephrine, dopamine and their metabolites, measured in urine and plasma, and serum chromogranin A served as tumour markers.

Results

All but 1 were evaluable for WBMTB; 74 patients had metastatic disease. ¹⁸F-dopa PET detected 979 lesions. SUV _max on ¹⁸F-dopa PET varied up to 29-fold between individual lesions within the same patients. WBMTB correlated with urinary serotonin ( r = 0.51) and urinary and plasma 5-HIAA ( r = 0.78 and 0.66). WBMTB also correlated with urinary norepinephrine, epinephrine, dopamine and plasma dopamine, but not with serum chromogranin A.

Conclusion

Tumour load per patient measured with ¹⁸F-dopa PET correlates with tumour markers of the serotonin and catecholamine pathway in urine and plasma in carcinoid patients, reflecting metabolic tumour activity.