Prostate cancer is now the most commonly diagnosed noncutaneous neoplasm in men. While there are many questions of profound clinical significance related to the management of this neoplasm, few are as critical as those regarding the limitations of current imaging modalities for clinicians involved in the management of these patients. As such, the thorough, if somewhat depressing, overview of the current status of imaging in prostate cancer by El-Gabry et al provides timely insight into both where we are and where we need to go.
Limitations of Current Imaging Modalities
As a backdrop to this article, it is important for the reader to understand why the limitations of current imaging modalities constrain our ability to provide optimal management of this disease. Accurate assessment of the local extent of disease is fundamentally important in the selection of appropriate local treatment modalities.
The prostate represents an organ that is "anatomically constrained" as it relates to the treatment of local disease extending beyond the prostate. As it is physically attached to the rectum, the bladder, and the urogenital diaphragm, any treatmentwhether it be surgical or radiotherapeuticthat attempts to treat these areas for local tumor is associated with substantial morbidity. Distinguishing patients who need more aggressive (albeit more morbid) efforts at local control from those whose disease is organ confined is critical to tailoring therapy to the needs of the individual patient. In other words, local tumor stage is the critical determinant of who gets what and how much.
A second issue touched upon in the article by El-Gabry et al is the ability of imaging modalities to detect the presence of disseminated disease. Both the high-risk, newly diagnosed patient and the patient with biochemical failure following primary therapy are affected by the limitations in available imaging modalities. Perhaps nowhere are these limitations more evident than in patients with biochemical recurrence following a primary therapy of curative intent. Given the fact that prostate-specific antigen recurrence may be detectable months if not years prior to the ability of imaging techniques to identify the site of disease recurrence, patients and clinicians are forced to make therapeutic decisions of potentially profound clinical import in a vacuum of objective data.
The failure of current imaging techniques to meet the needs of clinical practice hinges on the microscopic nature of both local disease extension and systemic disease spread. The appropriateness of a therapeutic decision may hinge upon the presence of a small number of neoplastic cells interspersed among normal adjacent tissue. In many cases, competing pathologic processes, such as inflammation and/or posttraumatic change, may produce tissue alterations that are indistinguishable from those resulting from tumor involvement. Finally, the very nature of testing strategies suggests that for a given test to have utility in an individual patient, diagnostic studies must have a level of sensitivity and specificity that is presently unmet by available imaging techniques.
What then is the future of imaging in prostate cancer? At some level, we must ask ourselves whether we are posing the correct question. Is it, in fact, imaging that is fundamentally flawed in its ability to detect microscopic local or systemic disease spread? Conversely, one might suggest that the limitations of available treatment modalities lie at the foundation of this clinical problem. That is, we may have unrealistic expectations of imaging as a result of our limited ability to deliver safe and effective curative therapy, irrespective of tumor stage.
My personal perspective is that limitations in areas of both imaging and treatment combine to hamper care delivery for the prostate cancer patient. As we consider the future, work must continue along both lines. However, specifically for the field of imaging, ongoing research and technology will need to work from "the edges" to narrow the number of patients with an "indeterminate" stage of the disease.
At present, I think that it is unrealistic to ask that imaging modalities function as binary end points for clinical decision-making. Rather, the additional information provided by imaging might best be utilized by integrating it into existing "risk nomograms" in an effort to capitalize on the information provided by multiple, clinically relevant variables.[3-5]