Emerging practice in the FDG-PET studies of testicular cancer

Objectives: 1. To review the value of FDG-PET in diagnosing, staging, and monitoring testicular cancers. 2. To assess the differences in FDG uptake between different forms of testicular cancers including seminomas such as spermatocytic seminomas along with non-seminomatous germ cell tumors such as embryonal carcinomas, yolk sac carcinomas, choriocarcinomas, and teratomas at the time of diagnosis and during treatment 3. To emphasize the difficulties in the qualitative and quantitive assessment of malignant lesions along with the new approaches taken to overcome the aforementioned barriers.

Methods: Multiple databases, including but not limited to Google Scholar, Web of Science, and PubMed, were accessed to compile a comprehensive body of literature related to the FDG-PET imaging of testicular cancer. Each study was evaluated for quality with respect to the methods applied, the number of subjects included, and the strength of findings. Limitations and other shortcomings will be noted as well. Thereafter, studies were categorized and synthesized to arrive at the overarching themes and findings.

Results: A significant number of FDG-PET studies have confirmed the value of qualitative data in accurately diagnosing testicular cancers. Moreover, there was a noted benefit in other studies of being able to identify metastases in adjacent or nearby structures. The previous standard of care for most testicular cancers, including seminomas, entailed radiotherapy along with systemic chemotherapy which increased the risk of secondary cancers and cardiovascular disease. Low volume metastatic disease after brief chemotherapy may be treated with surgery and retroperitoneal lymph node dissection (RPLND). In this context, FDG PET/CT has become the standard imaging required for pre-operative planning. Nevertheless, while FDG-PET proved useful in the initial diagnosis and staging of testicular cancers, many studies have shown FDG-PET as less sensitive in accurately predicting relapse; equivocal or positive findings may offer limited prognostic value. Nevertheless, negative findings after treatment strongly indicated against reoccurrence. Another difficulty has been the inability to accurately measure smaller tumors or metastatic lesions with traditional punch-biopsy or lesion-based methods; global analysis methods may provide a solution in many of these cases.

Conclusions: Testicular cancer is one of the most prevalent forms of cancer in young men. There is great interest in ensuring that lesions can be diagnosed at an early stage prior to progression. FDG-PET has shown great accuracy in diagnosing malignancies when structural imaging is inconclusive. Unlike diagnostic applications, there remain difficulties in deriving similar clinical value in the application of FDG-PET when measuring small lesions, reoccurrences, and treatment progress. Nevertheless, newer segmentation methods, such as global analysis, may provide a solution to these difficulties.