The goal in cancer care is evidence-based rather than empirical treatment selection. When the biopsy results are positive for prostate cancer, a wide variety of options for treatment may be considered, ranging from radical prostatectomy, to various forms of radiation therapy, to deferred treatment (i.e., “active surveillance,” a plan to defer definitive treatment until evidence of cancer progression).

Treatment selection should depend on the health and life expectancy of the patient, the patient’s preferences, and the risk posed by the cancer. Imaging can help to assess this risk.

Identifying potentially insignificant cancer
Earlier detection of prostate cancer with PSA screening has raised concerns about overdiagnosis and overtreatment. It is estimated that in the USA more than 30% of prostate cancer patients are overtreated [13]. Thus it is important to distinguish cancers that pose little or no risk to life and health (clinically “indolent” or insignificant cancers) from those that are potentially lethal (clinically significant) if left untreated.

A number of clinical variables (e.g., PSA, clinical stage, biopsy Gleason score) have proven to be valuable for assessing the risk of prostate cancer progression. Nomograms that combine these variables are more accurate than any single variable alone for predicting the pathologic stage of prostate cancer or the outcome of treatment [14, 15, 16], and they are often used for counseling patients during treatment selection. Several nomograms have been designed that use clinical variables to predict the presence of indolent prostate cancer (defined as organ-confined cancer with a total volume of 0.5 cm³or less and no poorly differentiated component on histology) [17, 18, 19, 20, 21, 22, 23]. Recently, Shukla-Dave et al. [24] developed nomogram models to predict the presence of insignificant prostate cancer in patients with clinically low-risk disease based on a combination of clinical variables and findings from MRI or combined MRI/MR spectroscopic imaging (MRSI) [24]. MRSI, which can be performed in the same examination as MRI using commercially available software, provides information about metabolic activity in the prostate and has been shown to increase the accuracy of MRI in prostate cancer detection, staging, and tumor volume estimation [25, 26, 27]. In the study by Shukla-Dave et al., MRI/MRSI findings were scored on a scale from 0 (definitely insignificant prostate cancer) to 3 (definitely significant prostate cancer) [24]. The nomogram models that incorporated MRI or MRI/MRSI scores performed significantly better than models based on clinical variables alone. Whereas the most comprehensive clinical model tested yielded an area under the receiver-operating characteristic curve (AUC) of 0.726, the models combining clinical variables with MRI and MRI/MRSI yielded AUCs of 0.803 (p < 0.018) and 0.854 (p < 0.001), respectively [24]. Although the new MR-based models are not sufficiently accurate to identify an indolent cancer unequivocally,  if validated prospectively, they may prove useful for counseling patients who are considering active surveillance [24]. For patients who choose active surveillance (e.g., every 2 years), serial MRI or MRI/MRSI can be used to identify new or growing lesions that should be assessed by biopsy. Furthermore, in patients with clinically low-risk, localized cancer, MRI may prove useful for identifying lesions suitable for focal therapy in the future. Assessing clinically significant prostate cancer For patients with clinically significant prostate cancer, imaging - in particular MRI or MRI/MRSI - can provide useful information for the selection and planning of treatment. The reported accuracy of MRI in the local staging of prostate cancer ranges from 54% to 93% [8, 28, 29, 30, 31, 32, 33]. On the whole, the accuracy of MRI in local staging has increased with time, most likely because of the maturation of MRI technology (e.g.,  faster imaging sequences,  more powerful gradient coils,  and post-processing image correction), better understanding of the morphologic criteria for diagnosing extracapsular extension and seminal vesicle invasion, and greater reader experience. The inclusion of findings from MRI or combined MRI/MRSI in prostate cancer staging nomograms has been shown to significantly improve the prediction of organ-confined disease and seminal vesicle invasion [34, 35]. Furthermore, two studies found that the addition of MRI to clinical variables improved the prediction of extracapsular extension, although the improvement was only significant when image interpretation was done by specialists in genitourinary MRI [31, 36]. ### Hedvig Hricak and Peter T. Scardino Prostate Cancer, eds. Hedvig Hricak and Peter T. Scardino. Published by Cambridge University Press. © Cambridge University Press 2009. ### REFERENCES

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