Objective To demonstrate whether ¹⁸F-FDG PET/CT metabolic parameters could predict prognosis in patients with metastatic maligant melanoma (MM).

Methods A retrospective analysis was conducted on a dataset composed of 47 patients who were newly diagnosed with metastatic MM and currently undergoing pretreatment ¹⁸F-FDG PET/CT in the Affiliated Hospital of Nanjing University Medical School, Nanjing Drum Tower Hospital from August 2011 to December 2018. Of 47 patients, 20 were male, 27 were female and median age 59 (23−86) years. All patients were treated with chemotherapy, immunotherapy or targeted therapy and follow-up time was 0.5 to 53.6 months. Melanoma-specific survival (MSS) and progression-free survival (PFS) were defined as the time from ¹⁸F-FDG PET/CT imaging to the patient's death and the patient's death or progression of the disease, separately. All patients underwent ¹⁸F-FDG PET/CT imaging before treatment.The maximum standardized uptake value (SUV_max) was measured. Whole-body metabolic tumor volume (MTV) and whole-body total lesion glycolysis (TLG) were measured automatically and SUV>40% SUV_max voxel boundary was used as threshold. The optimal thresholds of PET parameters were obtained using the receiver operating characteristic (ROC) curve, and the patients were divided into two groups separately according to the optimal thresholds of SUV_max, whole-body MTV and whole-body TLG and six groups were obtained. The difference of MSS and PFS between the two groups were predicted by Kaplan-Meier method and Log-rank test. Univariate analysis was conducted to evaluate the prognostic value of PET parameters and clinical variables. The Cox proportional risk model multivariate analysis was used to determine whether the PET parameters can act as independent prognostic risk factors for MSS and PFS.

Results The cut-off values for SUV_max, whole-body MTV, and whole-body TLG were 10.86, 8.12 cm³, and 91.45, respectively, as shown in the ROC curve analysis. The PFS was significantly different in two groups divided by optimal thresholds of whole-body MTV or whole-body TLG, separately (χ²=5.04, 5.02; both P<0.05). Similarly, the MSS was significantly different in two groups divided by optimal thresholds of SUV_max or whole-body TLG, separately (χ²=10.22, 4.38; both P<0.05). The univariate analysis results were as follows: the serum lactate dehydrogenase level≥245 U/L, lymphatic metastasis, SUV_max>10.86 and whole-body TLG>91.45, which were associated with predictors of MSS. M l stage, whole-body MTV>8.12 cm³ and whole-body TLG>91.45, which were associated with PFS. The multivariate analysis results showed that SUV_max>10.86, proving its potential as an independent prognostic risk factor for MSS.

Conclusion The ¹⁸F-FDG PET/CT metabolic parameter SUV_max was the best predictive marker in metastatic MM patients, whole-body MTV and whole-body TLG helped for the prognosis of metastatic MM patients.