Mobilization of CD34-positive tumour cells in a patient with testicular mixed germ cell tumour.

Tumour cells from a patient with recurrent testicular germ cell cancer and bone marrow infiltration were found to express CD33 and CD34 in the absence of other haemopoiesis-associated antigens. After myelosuppression and treatment with G-CSF for stem cell mobilization, CD34-positive tumour cells were detected in the peripheral blood in addition to normal haemopoietic progenitor cells. The tumour cells were decreased in the leukapheresis product. Retrospectively, the appearance of tumour cells in the peripheral blood after stem cell mobilization was the first indication of impending relapse.