Initial differential diagnosis can be undertaken when prostate cancer is suspected with ultrasonography and/or MRI using contrast agents, endorectal probes and image-guided biopsies. Results from imaging studies also provide important information on the extent of the disease and any potential regional and distant metastases in high-risk patients. The optimal method for imaging evaluation of men with PSA relapse (biochemical failure) is unresolved, but the goal of imaging is to determine if recurrence has occurred in the previously treated prostate bed or whether distant disease is present. The result will influence therapeutic management, including consideration of the use of salvage therapy for local recurrence and systemic treatment for metastatic disease.
Bone scintigraphy can be useful in detecting bone metastases, but the rate of false positives is relatively high;15
this technique cannot be used to detect the involvement of soft tissue or lymph nodes—sites to which prostate cancer cells commonly metastasize.
- ■ Generally, high uptake of 18F-fluorodeoxyglucose (FDG) is expected in prostate tumors that are poorly differentiated, hypoxic and have a high Gleason score
- ■ Glucose metabolism in prostate tumors is modulated by androgen; FDG-PET can, therefore, be useful in monitoring response to androgen deprivation therapy
- ■ FDG-PET has limited use in diagnosis and staging of clinically organ-confined disease and can be falsely negative or falsely positive
- ■ FDG-PET might be useful for diagnosing and staging primary tumors, detecting locally recurrent and/or metastatic disease, assessing the extent of metabolically active castrate-resistant disease, monitoring treatment responses and in prognostication
- ■ Results from the NOPR show that FDG-PET influenced clinical management in 35.1% of prostate cancer cases
- ■ Different PET radiotracers are likely to be suited to various clinical states of prostate cancer, taking advantage of the most relevant biological markers of disease
Newer imaging methods, such as 111
In-capromab pendetide scintigraphy (a technique using a radiolabeled antibody that targets prostate-specific membrane antigen [PSMA], the levels of which are upregulated in hormone-resistant states and in metastatic disease) can be used to help with management decisions in a select group of men at high risk for recurrent and metastatic spread. Despite this utility, the technique also has drawbacks: it has a limited predictive value when used to image the prostate fossa, particularly following radiation therapy; it shows low sensitivity for detecting osseous metastases; furthermore, the technique is demanding and the results require interpretation by skilled and experienced staff.16,17
High-resolution MRI using lymphotropic superparamagnetic nanoparticles might also allow the detection of small, and otherwise undetectable, lymph node metastases in patients with prostate cancer.18
However, the exact clinical use of this diagnostic imaging approach in a diverse group of patients still needs to be determined.
The role of PET using FDG as a tracer is undoubtedly important in the assessment of cancer patients. The development of hybrid PET–CT imaging systems (which can precisely localize metabolic abnormalities and characterize the metabolic activity of normal and abnormal structures, thereby increasing diagnostic confi dence and reducing equivocal image interpretations), the presence of regional distribution centers for FDG, expanding clinical experience, and improved reimbursement have all facilitated the use of FDG-PET and PET–CT in cancer imaging. FDG-PET is widely used for diagnosis, initial staging, restaging, prediction and monitoring of treatment response, surveillance and prognostication in a variety of cancers, and this use has led to improved clinical decision-making and cost-effective management changes in substantial numbers of patients.19-21
Investigations into the potential use of PET and PET–CT to assess various clinical aspects of prostate cancer are being undertaken. Interestingly, in summaries of the findings of the National Oncologic PET Registry (NOPR),22
the enrollment rates for patients with prostate cancer were among the highest of all cancers studied.23,24