Dr. Tan began with a short overview of seminoma. Approximately 25% of patients present with advanced clinical stage disease. After chemotherapy, approximately 66% of patients have residual masses. Masses larger than 3 cm have a 41% risk of harboring viable residual tumor, while masses smaller than 3 cm, have an 8% risk of viable residual tumor. The disease-free survival with recurrent/progressive disease is around 45%. The answer to the controversial question of whether we should intervene on all residual masses> 3 cm is still not known. Treating all patients will result in over treatment in 55% of patients with the associated resulting morbidity of this surgery. It is known that re-imaging with interval decrease in tumor size is not reliable for prediction of viable tumor, and performing a biopsy of the lesion is not reliable.
Dr. Tann continued and discussed the role of FDG PET in post-chemothearpy seminoma. Figure 1 demonstrates the decreasing positive predictive value (PPV) of the FDG-PET that has been reported through the years. Due to this low PPV, an approach of “wait and see” should be adopted according to Dr. Tan (Figure 2), which includes a wait time of at least 6 weeks, before making a decision on how to move forwards.
Dr. Tann continued to discuss the role of imaging in post-chemothearpy in non-seminoma germ cell tumors (NSGCT). Post-chemotherapy masses in NSGCT harbor necrosis in 40% of cases, 40% harbor mature teratoma, and 20% have viable carcinoma. Unfortunately, FDG PET does not help here and it is recommended to perform a resection of all lesions larger than 1 cm.
Dr. Tann discussed several tips on the usage of the various imaging modalities (CT, MRI, and PET) in GCTT. CT imaging should be the technique of choice in staging of GCTT. This is due to its low price, high accessibility and short performance time. In the initial staging scans, the cutoff of 8 mm in the max short axis diameter should be used. MRI has the same accuracy for nodal identification as CT. Lastly, FDG PET should be used for problem solving (when there are equivocal findings on baseline staging imaging, follow-up in the presence of raised marker levels, and when there are negative imaging findings).
Dr. Tann concluded his talk by stating that FDG PET has high negative predictive value for post-chemo seminoma GCTT assessment, but PPV is limited; there is a need for additional follow-up before therapy/surgery. FDG PET does not have a role for post-chemothearpy NSGCT, but may be useful for problem solving later on. CT scans should be the primary imaging modality, and more specific PET markers are needed.
Figure 1 – The Role of FDG PET in Post-chemothearpy Seminoma Patients
Figure 2 – “Wait and see” Approach in Post-chemothearpy PET Positive Mass
Presented by: Mark Tann, MD Indiana University School of Medicine
Written by: Hanan Goldberg, MD, Urologic Oncology Fellow (SUO), University of Toronto, Princess Margaret Cancer Centre @GoldbergHanan at the 2018 American Society of Clinical Oncology Genitourinary (ASCO GU) Cancers Symposium, February 8-10, 2018 - San Francisco, CA