Carbon 11–labeled methionine positron emission tomography for detection of residual viable tumor cells after adjuvant therapy in nongerminomatous malignant germ cell tumors in 2 cases including an autopsy case

Abstract

Background The treatment of intracranial NGMGCTs is generally based on chemotherapy and radiotherapy. To avoid the potential of tumor recurrence, we normally have the residual mass lesion removed after adjuvant therapy. However, since 1988 we have treated 15 patients with NGMGCT and pathologically evaluated 12 such patients after adjuvant therapy by a new method we have developed and found viable tumor cells in 4 (33%) of 12 patients. Based on our experience, therefore, we feel we have been able to develop a reliable diagnostic tool for confirming the presence or absence of viable tumor cells in residual mass after adjuvant therapy for patients with NGMGCT. Case Description We describe here 2 patients with NGMGCTs who underwent MET-PET. Patient 1 was an 11-year-old boy with immature teratoma. On gadolinium (Gd)-enhanced magnetic resonance imaging (MRI), a high-intensity area was found in his right cerebellar hemisphere and a high uptake in MET-PET was confirmed in the same region. We judged it as the recurrence of the tumor. Finally, he died and was autopsied. Patient 2 was a 16-year-old girl with an NGMGCT who received combined chemo- and radiotherapy that led to a reduction in the volume of the tumor. Her serum β-HCG and HCG levels also returned to the reference range. However, the mass did not disappear and another MRI scan disclosed a residual Gd-enhanced lesion. To assess whether there were residual viable tumor cells, MET-PET was performed, and it demonstrated no hyper-uptake region in the residual mass. We, therefore, did not surgically remove the mass and kept the patient under observation. There has not been any tumor recurrence in this patient for more than 2 years. Conclusion In these 2 cases, the increased MET uptake was more specific of tumor tissue and more accurate than MR Gd enhancement. MET-PET may be a useful diagnostic tool for predicting viable tumor cells after adjuvant therapy in patients with NGMGCT, thus allowing further surgical intervention.