Positive Correlation Between 18F-FDG Uptake and Tumor-Proliferating Antigen Ki-67 Expression in Adrenocortical Carcinomas

Adrenocortical carcinoma (ACC) is an extremely rare endocrine malignancy, which cannot always be diagnosed during conventional radiology and hormonal investigations. 18 F-FDG PET could help predict malignancy, but more data are necessary to support future guidelines.A cohort of 63 patients with histologically proven ACC (n = 55) or metastatic ACC with steroid oversecretion (n = 8) was assembled. All patients underwent an 18 F-FDG PET, and the SUV max and the adrenal-to-liver SUV max ratio were calculated. The 18 F-FDG PET parameters were compared with clinical, pathological, and outcome data.Fifty-six of 63 patients (89%) had an ACC with an adrenal-to-liver SUV max ratio >1.45, which was a previously defined cutoff value to predict malignancy with 100% sensitivity. Seven ACCs (11%) had a lower uptake (adrenal-to-liver SUV max <1.45), most of them with a proliferation marker Ki-67 expression level <10%. A positive correlation between 18 F-FDG PET parameters (SUV max and adrenal-to-liver SUV max ratio) and tumor size, ENSAT (European Network for the Study of Adrenal Tumors) staging, total Weiss score, and the Ki-67 was found. The strong correlation between SUV max and Ki-67 ( r = 0.47, P = 0.0009) suggests a relationship between 18 F-FDG uptake levels and tumor proliferation. No statistically significant associations between outcome parameters (progression-free or overall survival) and 18 F-FDG PET parameters were found.This large cohort study shows that most cases of ACC demonstrate high 18 F-FDG uptake. However, the positive correlation observed between SUV max and Ki-67 expression levels seems to explain the possibility of identifying some ACC with a low or inexistent 18 F-FDG uptake. These findings have practical implications for the management of patients with an adrenal mass.