Clinical diagnostic value of serum β-hCG and AFP in mediastinal germ cell tumor

Objective To explore the clinical diagnostic value of serum human chorionic gonadotropin beta subunit (β-HCG) and alpha fetoprotein (AFP) in mediastinal germ cell tumors. Methods A retrospective analysis was conducted on the patients who were definitely diagnosed as mediastinal tumors or mediastinal neoplastic lesions. A total of 133 patients were included for analysis between January 2008 and May 2014, divided into two groups.42 cases of mediastinal germ cell tumor patients were marked as case group while 91 cases of other mediastinal tumor or mediastinal neoplastic lesion patients were marked as control group (including 31 cases of thymoma, 10 cases of mediastinal neurogenic tumor, 2 cases of intrathoracic goiter, 25 cases of mediastinal cyst, 2 cases of mediastinal lipoma, 11 cases of mediastinal lymphoma and 10 cases of thymic carcinoma). AFP was detected by chemiluminescence detection, and -HCG was detected by electrochemical luminescence. K-S test was performed to investigate normality of data, non-normally distributed data were described as Median (interquartile range). Mann-Whitney U test was done for measurement of data between two groups. Logistic regression analysis was performed as multivariate analysis. Receiver operating characteristic curve(ROC)was used to determine the cut-off values. Results The levels of serum AFP and β-HCG in case group were 13.26 (2.39–48.09) ng/ml and 1.99 (0.10–15.7) IU/L, respectively, significantly higher than those in control group[AFP: 2.47 (1.78–3.16) ng/ml, β-HCG: 0.10 (0.10–0.55) IU/L]. The difference of levels of AFP and β-HCG between the case group and the control group were statistically significant (P=0.000). There were no significant difference when it comes to β-HCG between the case group and intrathoracic goiter patients in control group. Apart from it, the difference of levels of AFP and β-HCG between the case group and every single control group were statistically significant. Cut-off values of AFP and β-HCG for distinguishing mediastinal germ cell tumors from mediastinal tumors were 5.07 ng/ml and 2.32 IU/L. In this scenario, for AFP and β-HCG, sensitivity were 57.1% and 50%, specificity were 97.8% and 96.7%, accuracy were 54.9% and 46.7%, area under the curve (AUC) were 0.773 and 0.755, positive likelihood ratios were 26.00 and 15.17respectively. Parallel experiments contributed to increase the sensitivity to 71.4%. Predictive probability (P)=1/[1+ exp (–0.319AFP–0.253HCG+ 2.850)] was obtained by logistic regression model. When cut-off value of predictive probability (P) was 0.30, specificity, AUC, and positive likelihood ratio were increased to 98.9%, 0.835 and 65.00respectively, negative likelihood ratio was decreased to 0.29, positive predictive value and negative predictive value were increased also (96.8% and 88.2% respectively). Conclusion Serum β-HCG, AFP and predictive probability ( P ) is valuable in the diagnosis of mediastinal germ cell tumor.(Chin J Lab Med, 2015, 38: 677-681) Key words: Mediastinal neoplasms; Neoplasms, germ cell and embryonal; Chorionic gonadotropin, beta subunit, human; alpha-Fetoproteins