Detecting Metastases by PyL PET/CT in Subjects Starting Enzalutamide for Untreated Castration Resistant Prostate Cancer.

Prostate cancer (PCa) is the most common solid organ cancer in North American men and is initially androgen sensitive. Therefore, castration and/or androgen receptor blockade remains the central palliative treatment once PCa has metastasized or failed to locoregional therapies. Because androgen deprivation therapy is not curative, all patients will eventually progress to the metastatic castration-resistant prostate cancer state. About 5% of prostate cancers will be metastatic by conventional imaging techniques at diagnosis while most patients achieving CRPC state will first be localized and then progress to metastatic state later in the disease course. Therefore, a significant proportion of patients will progress through an intermediary state of disease defined as the non-metastatic CRPC state (M0CRPC). Over the last year and a half, M0CRPC treatment landscape has completely changed with demonstrating the benefits of second-generation antiandrogens (darolutamide, enzalutamide and apalutamide) to prevent progression of M0CRPC patients. Enzalutamide have then been approved by the Federal Drug Administration and Health Canada for the treatment of M0CRPC. On the other hand, conventional imaging techniques based on bone turnover (bone scan (BS)) or anatomical features (magnetic resonance imaging (MRI) or computed tomography (CT)) have important limitations and poor accuracy. Bone scans (BS) is the commonest imaging technique used to detect bone metastases in the clinics. BS does not image directly cancer cells, but the effect of cancer on the bone. Other pathologies such as fractures, degenerative arthritis and other benign bone lesions can also cause focal uptake on BS and lead to false-positive results. Another drawback of BS is its poor sensitivity to image small metastases confined to bone marrow. These limitations stress the importance to improve PCa imaging by using new imaging modalities. Because novel agents targeting the androgen synthesis and receptor axis (e.g. enzalutamide), bone metastasis (radium-223) and microtubules assembly (docetaxel, cabazitaxel) have been shown to increase metastatic CRPC patients overall survival, a burning question is to determine if the non-metastatic CRPC status is real. There is growing evidence that newer imaging techniques using positron emission tomography can improve metastasis detection accuracy and may refine PCa patient prognostic stratification and treatment eligibility.