Combined magnetic resonance imaging and spectroscopy in the assessment of high grade prostate carcinoma in patients with elevated PSA: A single-institution experience of 356 patients
Introduction
Serum prostate-specific antigen (PSA) is one of the corner stones of prostate cancer detection in the general population. However, depending on the chosen PSA threshold, a significant number of subjects with elevated PSA do not have prostate cancer and up to 40% of the detected cancers are clinically insignificant [1], [2]. Since clinical significance is, among others, closely related to high Gleason grade [3], a non-invasive test that could detect or exclude such areas throughout the prostate would be of great help in both the selection of patients for active surveillance, or in the decision to rebiopsy patients with prior negative transrectal biopsies.
T2-weighted magnetic resonance imaging (MRI) is able to assess the presence and extent of low signal intensity prostate carcinoma surrounded by high signal intensity normal peripheral zone tissue [4]. Furthermore, magnetic resonance spectroscopy imaging (MRSI) detects low citrate levels and high choline levels in prostate carcinoma. In a previous study, we showed a better diagnostic performance for both modalities combined (MRI + MRSI) than for MRI alone or MRSI alone [5]. In a recent meta-analysis, MRI + MRSI had an overall pooled sensitivity and specificity on patient level of 82% and 88%, respectively [6].
A correlation between higher Gleason grades and morphologic features on MRI has been reported [7]. A similar correlation exists between tumor aggressiveness and metabolic profile on MRSI [8]. Taking advantage of both observations, MRI + MRSI might become an important tool to diagnose high grade cancers, rather than prostate cancers in general.
The purpose of our study was to retrospectively investigate the ability of whole-prostate MRI + MRSI to detect or exclude high grade prostate carcinoma (Gleason 4 + 3 or higher) in a large cohort of patients presenting with elevated PSA.
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Patients
The study population consisted of 356 subjects (mean age 63.5 years, range 42–81 years) with a mean PSA of 11.5 ng/ml (median 8.0 ng/ml, range 0.4–133.0 ng/ml), either or not with abnormal DRE and/or abnormal transrectal ultrasound. They all underwent whole-prostate magnetic resonance imaging and spectroscopy imaging (MRI + MRSI) between March 2002 and September 2007, and had either histopathological verification or at least 12 months clinical follow-up. They were referred for diagnosis (no previous
Results
Overall, the positive predictive value of MRI + MRSI for the diagnosis of prostate cancer (of any grade) in men with elevated PSA was 94.1% (Table 3). The sensitivity of MRI + MRSI for high grade tumors (92.7%) was significantly higher than for lower grade tumors (67.6%) (p = 0.001, χ2-test). MRI + MRSI claimed a high grade carcinoma in 67.6% of patients with a lower grade tumor, but only in 7.4% of subjects with no evidence of prostate cancer, respectively. Of all such “incorrect” claims, 92.4%
Discussion
PSA testing increases the detection rate of prostate cancer, but also leads to the diagnosis of cancers that are clinically insignificant [1], [2]. Annual PSA testing from ages 55 to 67 years has been reported to yield insignificant cancers in approximately half of all men diagnosed with localized prostate cancers [19]. Therefore, a non-invasive method that covers the whole prostate and that allows identification of patients with a low risk of high grade tumors is highly desirable.
In 2000,
Conclusion
MRI + MRSI can exclude a Gleason score 4 + 3 or higher grade cancer in patients with elevated PSA with high probability. It may thus become a very useful tool in the selection of patients for active surveillance or for avoiding repeat biopsies. These single-institution results warrant further exploration.
Conflict of interest
None.
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