Definition of variables
The following data were collected from the electronic and paper medical records: age, antecedent pregnancy, interval from antecedent pregnancy to chemotherapy, pre-therapy serum β-hCG, tumor size including uterus, metastases (lung, kidney, liver, brain, other), number of metastases, previous chemotherapy failure, FIGO stage, and FIGO score. Details of pre-therapy CSF hCG (only for brain metastases), as well as treatment and outcome for GTN patients with liver or brain metastases, were also abstracted from the medical records. Serum β-hCG level <5 IU/L was set as the cutoff for a normal value in this study; this was determined using a kit (Beckman Coulter, Inc., Chaska, MN USA). Early death was defined as death occurring within four weeks of treatment initiation.