Prostate cancer: is inapparent tumor at endorectal MR and MR spectroscopic imaging a favorable prognostic finding in patients who select active surveillance?

Abstract

Purpose: To retrospectively determine whether inapparent tumor at endorectal magnetic resonance (MR) imaging and MR spectroscopic imaging is a favorable prognostic finding in prostate cancer patients who select active surveillance for management.

Materials and methods: Committee on Human Research approval was obtained and compliance with HIPAA regulations was observed, with waiver of requirement for written consent. Ninety-two men (mean age, 64 years; range, 43-85 years) were retrospectively identified who had biopsy-proved prostate cancer, who had undergone baseline endorectal MR imaging and MR spectroscopic imaging, and who had selected active surveillance for management. Their mean baseline serum prostate-specific antigen (PSA) level was 5.5 ng/mL, and the median Gleason score was 6. Two readers with 10 and 3 years of experience independently reviewed all MR images and determined whether tumor was apparent on the basis of evaluation of established morphologic and metabolic findings. Another investigator compiled data about baseline clinical stage, biopsy findings, and serum PSA measurements. Multiple logistic regression analysis was used to investigate the relationship between the clinical parameters and tumor apparency at MR imaging and the biochemical outcome.

Results: At baseline MR imaging, readers 1 and 2 considered 54 and 26 patients, respectively, to have inapparent tumor (fair interobserver agreement; kappa = 0.30). During a mean follow-up of 4.8 years, 52 patients had a stable PSA level and 40 had an increasing PSA level. In multivariate analysis, no significant association was found between the baseline clinical stage, Gleason score, serum PSA level, or the presence of apparent tumor at endorectal MR imaging and MR spectroscopic imaging for either reader and the biochemical outcome (P > .05 for all).

Conclusion: Endorectal MR imaging and MR spectroscopic imaging findings of tumor apparency or inapparency in prostate cancer patients who select active surveillance for management do not appear to be of prognostic value.

Figure 1:

Photomontage shows representative example of biopsy-proved prostate cancer that is not apparent at endorectal MR imaging and MR spectroscopic imaging (radiologic stage T1 disease). Left: Transverse T2-weighted fast spin-echo MR image (5000/96 [effective]) shows no masslike foci of low signal intensity suggestive of tumor. Overlying grid corresponds to adjacent MR spectral array shown at right. Right: Metabolic patterns without abnormalities. In representative peripheral zone voxel, arrow pointing right shows nonelevated choline peak and arrow pointing left shows appropriately high citrate peak.

Figure 2:

Photomontage shows representative example of prostate cancer that is apparent at endorectal MR imaging and MR spectroscopic imaging. Left: Transverse T2-weighted fast spin-echo MR image (5000/96 [effective]) shows ill-defined masslike focus (vertical arrow) of low signal intensity in left peripheral zone interpreted as organ-confined tumor (radiologic stage T2 disease) by both readers. Overlying grid corresponds to adjacent MR spectral array shown at right. Right: Metabolic patterns consistent with malignancy. Voxels corresponding to low T2 signal intensity focus in left peripheral zone demonstrate markedly elevated choline peaks (horizontal arrows).

Figure 3:

Percentage of patients with biochemical progression, as a function of baseline stage at MR imaging for both readers.