The variable transformation in metastases from testicular germ cell tumors: the need for selective biopsy.

The propensity for metastatic testicular teratocarcinoma to undergo differentiation, particularly when associated with successful cancer chemotherapy, means that the histology of residual disease following chemotherapy cannot be assumed without biopsy. We present 4 cases in which biopsy of a metastasis was important in determining the management of the patient. We conclude that because of the variable nature of the transformation of metastases in testicular germ cell tumors, particularly after chemotherapy, residual disease will often need further biopsy to establish whether it represents residual malignant disease or benign transformation.