Introduction:

There is no way to reliably differentiate between fibrosis/necrosis, teratoma, and viable germ cell tumor in patients receiving post-chemotherapy retroperitoneal lymph node dissection (RPLND) for non-seminomatous germ cell tumor (NSGCT). Functional imaging, including ¹⁸F-Fludeoxyglucose (¹⁸F-FDG) positron emission tomography (PET), has been disappointing in this space. Due to the need for better imaging modalities in patients receiving RPLND, we designed a prospective study using anti-1-amino-3-¹⁸F-fluorocyclobutane-1-carboxylic acid, a synthetic radiolabeled leucine amino acid analog which is commonly referred to as anti-¹⁸F-FACBC (Axumin^TM, Blue Earth Diagnostics, Ltd. Oxford, UK). Our prospective study aims to investigate the accuracy of Axumin PET/CT in detecting residual tumor prior to retroperitoneal lymph node dissection (RPLND).

Methods:

From March 2018 – May 2019, 10 eligible patients were enrolled and underwent pre-operative Axumin PET/CT prior to undergoing bilateral full template RPLND or excision of mass (in one case of re-do pelvic lymph node dissection). RPLND packets from each location were sent as separate specimens and appropriately labeled with the origin of the packet. Correlation between Axumin PET/CT and RPLND pathology were evaluated on per patient and per packet level.

Results:

A total of 10 patients (age 29 ± 7.6 yrs) underwent Axumin PET/CT prior to surgery. 9/10 patients have undergone chemotherapy prior to RPLND (See Table 1 for baseline characteristics). Correlation between Axumin PET/CT and RPLND pathology was seen in 4/10 (40%) of patients.  6/10 patients (60%) with negative Axumin PET/CT were to found have residual disease on RPLND, with 1 patient with seminoma and 5 patients with teratoma (Table 2). Compared to the reference standard of RPLND, Axumin PET/CT has 14% sensitivity, 100% specificity, positive predictive value of 100% and negative predictive value of 33% in these 10 patients. No patients experienced any adverse events as a direct result of undergoing an Axumin PET/CT.

Conclusion:

Current management of NSGCT is heavily reliant on sub-optimal imaging modalities that are unable to accurately distinguish between post-chemotherapy necrosis/fibrosis versus viable germ cell tumor and/or teratoma. Despite a different mechanism of action from ¹⁸F-FDG, anti-¹⁸F-FACBC has low sensitivity for residual teratoma in the retroperitoneum. However, one patient with positive Axumin PET/CT after prior RPLND had embryonal rhabdomyosarcoma on resection of the recurrent mass, suggesting the need for further evaluation of the role of Axumin PET/CT in NSGCT.

Funding: N/A