Application Of Preoperative ¹⁸F-FDGPET/CT Imaging In Acral Melanoma

Objective:To investigate the value of preoperative ¹⁸F-Fludeoxyglucose(¹⁸F-FDG)PET/CT imaging in diagnosis and staging of acral malignant melanoma.Methods:The preoperative ¹⁸F-FDG PET/CT findings and clinical data of 40 patients with acral malignant melanoma confirmed pathologically were retrospectively analyzed.The¹⁸F-FDG PET/CT imaging indexes included Maximal Standard Uptake Value(SUV_max),Maximal lymph node diameter（short diameter of the largest lymph node）,lymph node grade.The lymph node grade was divided into 6 grades based on lymph node morphology,structure,size and FDG metabolism.Clinical data included age,sex,primary pathological indicators（Breslow thickness,T stage,presence of ulcers,mitotic rate）,etc.Using Receiver Operating characteristic curve（ROC）analysis,the correlation analysis between primary pathological indicators and ¹⁸F-FDG PET/CT imaging indicators and the final pathological diagnosis results of lymph nodes was conducted,and the optimal threshold was obtained.The final pathological diagnosis of lymph nodes was used as the gold standard to evaluate the diagnostic efficacy,and the sensitivity,specificity and accuracy were calculated.The final pathological of lymph nodes was taken as the dependent variable,and age,gender,Breslow thickness,mitotic rate,presence of ulcer,PET/CT lymph node grade,SUV_max value,and maximum diameter of lymph nodes were taken as independent variables.Two-class stepwise Logistic regression analysis was performed to clarify the independence of diagnostic indexes.Kaplan-meier analysis was used for survival analysis,and the relationship between Breslow thickness,mitotic rate and progression-free survival（PFS）was analyzed.Log-rank test was used for comparison between groups.P<0.05 was considered statistically significant.Result:Of the 40 patients,36 underwent surgical treatment（25 with no lymph node metastasis and 11 with lymph node metastasis）,and 4 underwent comprehensive treatment for distant metastasis.The primary pathological indexes（Breslow thickness,mitosis rate,T stage）were significantly different between the two groups with and without lymph node metastasis（P<0.05）.ROC curve analysis showed that the area under the curve（AUC）of Breslow thickness,T stage and mitosis rate predicting lymph node metastasis was 0.778（P=0.009;95%CI:0.618～0.939）,0.780（P=0.008;95%CI:0.624～0.936）and 0.698（P=0.061;95%CI:0.495～0.902）.The optimal thresholds were 3.9mm,3.5 and 6.5/mm²,respectively.Based on Breslow thickness≥3.9mm,T staging≥3.5 and mitosis rate≥6.5/mm²,the sensitivity,specificity and accuracy of lymph node metastasis were 81.8%,72.7%and 54.5%;68.0%,76.0%and 88.0%;74.9%,74.4%and 71.3%,respectively.The AUC of SUV_max,maximum diameter of lymph node,and PET/CT lymph node grade for lymph node metastasis were 0.875（P=0.004;95%CI:0.701～1.000）,0.792（P=0.025;95%CI:0.593～0.991）and 0.940（P=0.001;95%CI:0.687～1.000）.The optimal thresholds were 2.1,1.4cm and 3.5,respectively.And based on SUV_max≥2.1,maximum diameter of lymph node≥1.4cm and PET/CT lymph node grade≥3.5,the sensitivity,specificity and accuracy of lymph node metastasis were 88.9%,55.6%and 77.8%;88.3%,91.7%and 100%;86.1%,73.7%and 82.4%respectively.Two-class stepwise Logistic regression analysis showed that PET/CT lymph node grade had independent diagnostic significance for lymph node metastasis（β=2.132,Wald value=4.679,OR=8.432,P=0.031）.Log-rank analysis showed that PFS in Breslow≥3.9mm and mitosis rate≥6.5 mm²groups were both lower than that in Breslow<3.9mm and mitosis rate<6.5 mm² groups but the difference was not statistically significant（χ²=3.544,P=0.06;χ²=0.647,P=0.421 respectively）.Conclusion:¹⁸F-FDG PET/CT is recommended for patients with acral malignant melanoma whose primary lesions has Breslow thickness≥3.9mm and mitotic rate≥6.5/mm².For lymph nodes with SUVmax≥2.1 or maximum diameter≥1.4cm revealed by ¹⁸F-FDG PET/CT imaging,the possibility of metastasis should be considered.Preoperative¹⁸F-FDG PET/CT is helpful for accurate staging and treatment strategy of acral malignant melanoma.