Imaging Prostate Cancer: Current and Future Applications
Prostate cancer is now the most commonly diagnosed noncutaneous neoplasm in men.[1] 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.
Prostate cancer is now the mostcommonly diagnosed noncutaneous neoplasm in men.[1] While there are many questions of profound clinicalsignificance related to the management of this neoplasm, few are as critical asthose regarding the limitations of current imaging modalities for cliniciansinvolved in the management of these patients. As such, the thorough, if somewhatdepressing, overview of the current status of imaging in prostate cancer byEl-Gabry et al provides timely insight into both where we are and where we needto go.
Limitations of CurrentImaging Modalities
As a backdrop to this article, it is important for the reader tounderstand why the limitations of current imaging modalities constrain ourability to provide optimal management of this disease. Accurate assessment ofthe local extent of disease is fundamentally important in the selection ofappropriate local treatment modalities.
The prostate represents an organ that is "anatomicallyconstrained" as it relates to the treatment of local disease extendingbeyond the prostate. As it is physically attached to the rectum, the bladder,and the urogenital diaphragm, any treatmentwhether it be surgical orradiotherapeuticthat attempts to treat these areas for local tumor isassociated with substantial morbidity. Distinguishing patients who need moreaggressive (albeit more morbid) efforts at local control from those whosedisease is organ confined is critical to tailoring therapy to the needs of theindividual patient. In other words, local tumor stage is the criticaldeterminant of who gets what and how much.
A second issue touched upon in the article by El-Gabry et al isthe ability of imaging modalities to detect the presence of disseminateddisease. Both the high-risk, newly diagnosed patient and the patient withbiochemical failure following primary therapy are affected by the limitations inavailable imaging modalities. Perhaps nowhere are these limitations more evidentthan in patients with biochemical recurrence following a primary therapy ofcurative intent. Given the fact that prostate-specific antigen recurrence may bedetectable months if not years prior to the ability of imaging techniques toidentify the site of disease recurrence, patients and clinicians are forced tomake therapeutic decisions of potentially profound clinical import in a vacuumof objective data.[2]
The failure of current imaging techniques to meet the needs ofclinical practice hinges on the microscopic nature of both local diseaseextension and systemic disease spread. The appropriateness of a therapeuticdecision may hinge upon the presence of a small number of neoplastic cellsinterspersed among normal adjacent tissue. In many cases, competing pathologicprocesses, such as inflammation and/or posttraumatic change, may produce tissuealterations that are indistinguishable from those resulting from tumorinvolvement. Finally, the very nature of testing strategies suggests that for agiven test to have utility in an individual patient, diagnostic studies musthave a level of sensitivity and specificity that is presently unmet by availableimaging techniques.
Conclusions
What then is the future of imaging in prostate cancer? At somelevel, we must ask ourselves whether we are posing the correct question. Is it,in fact, imaging that is fundamentally flawed in its ability to detectmicroscopic local or systemic disease spread? Conversely, one might suggest thatthe limitations of available treatment modalities lie at the foundation of thisclinical problem. That is, we may have unrealistic expectations of imaging as aresult of our limited ability to deliver safe and effective curative therapy,irrespective of tumor stage.
My personal perspective is that limitations in areas of bothimaging and treatment combine to hamper care delivery for the prostate cancerpatient. As we consider the future, work must continue along both lines.However, specifically for the field of imaging, ongoing research and technologywill need to work from "the edges" to narrow the number of patientswith an "indeterminate" stage of the disease.
At present, I think that it is unrealistic to ask that imagingmodalities function as binary end points for clinical decision-making. Rather,the additional information provided by imaging might best be utilized byintegrating it into existing "risk nomograms" in an effort tocapitalize on the information provided by multiple, clinically relevantvariables.[3-5]
References:
1. Greenlee RT, Murray, Bolden S, et al: Cancer statistics,2000. CA: Cancer J Clin 50(1):7-33, 2000.
2. Pound CR, Partin AW, Eisenberger MA, et al: Natural historyof progression after PSA elevation following radical prostatectomy [seecomments]. JAMA 281(17):1591-1597, 1999.
3. Kattan MW, Eastham JA, Stapleton AM, et al: A preoperativenomogram for disease recurrence following radical prostatectomy for prostatecancer. J Natl Cancer Inst 90(10):766-771, 1998.
4. D’Amico AV, Whittington R, Malkowicz SB, et al: Combinationof the preoperative PSA level, biopsy Gleason score, percentage of positivebiopsies, and MRI T-stage to predict early PSA failure in men with clinicallylocalized prostate cancer. Urology 55(4):572-577, 2000.
5. Polascik TJ, Pearson JD, Partin AW: Multivariate models aspredictors of pathological stage using Gleason score, clinical stage, and serumprostate-specific antigen. Semin Urol Oncol 16(3):160-171, 1998.
