Aritrick Chatterjee1, Xiaobing Fan1, Ambereen Yousuf1, Tatjana Antic2, Gregory Karczmar1, and Aytekin Oto1
1Department of Radiology, University of Chicago, Chicago, IL, United States, 2Department of Pathology, University of Chicago, Chicago, IL, United States
Synopsis
This
study investigates whether quantitative MRI of the prostate reveals differences
between ethnicities that can affect diagnosis. This study shows that the different
ethnicities, specifically AAs and CAs have different quantitative MRI values
that affects the utility of MRI in the diagnosis of PCa. Different thresholds
are needed for PCa diagnosis for different ethnicities. Despite more high grade
lesions in AA, the ADC and T2 for lesions in AA were nominally higher than in
CA. DCE-MRI significantly improves differentiation of PCa from benign tissue in
AA, due to significantly higher cancer signal enhancement rate in AA compared
to CA.
Introduction
Men with a family history of prostate cancer (inherited risk
factors), genetic risk factors (germline mutations – BRCA2 gene), and specific
race (African ancestry) have an elevated risk for developing prostate cancer (1). African Americans (AA) have higher risk
for prostate cancer (PCa) compared to Caucasian Americans (CA). In addition, the mortality rate is also higher in AAs
even after adjusting for prognostic factors (2,3). A
recent study found that racial disparities were greatest in non-clinically
significant low-grade Gleason 6 disease, in which AA men were twice as likely
to die of PCa compared with men from other ethnicities (4).
MRI has the potential to play an important role in the
diagnosis and management of prostate cancer (PCa). A
recent study by Mahran et. al. (5) showed racial disparity in the utility of qualitative
multi-parametric MRI for the diagnosis for PCa. However, high inter-observer
variability in the qualitative interpretation of prostate mpMRI remains a
concern (6). There are no
studies that have evaluated quantitative MRI as a biomarker to identify the racial
differences in PCa biology and determine the utility of MRI specifically for different
populations. Whether PCa’s have
different biology and MR characteristics in AA versus CA men has yet to be
determined. Therefore, this study investigates whether quantitative MRI of the
prostate reveals differences between ethnicities that can affect diagnosis.Materials and Methods
This
IRB approved study involved retrospective analysis of prospectively acquired
data. Patients (47 CA, 12 AA) with biopsy confirmed PCa underwent preoperative
prostate mpMRI on 3T Philips Achieva scanner using a 6-channel cardiac phased
array coil placed around the pelvis combined with an endorectal coil (Medrad,
Bayer Healthcare) prior to undergoing radical prostatectomy. The protocol included T2-weighted (T2W),
multi-echo T2-weighted, diffusion weighted and dynamic contrast enhanced (DCE)
images (see Table 1). Quantitative mpMRI metrics: ADC, T2 and DCE-MRI
parameters from empirical mathematical model (7) parameters: signal
enhancement (α) and washout rates (β) were calculated for ROIs on sites of
prostatectomy-verified PCa and normal tissue (peripheral and transition zone). Lesions
smaller than 5mm on pathology were excluded. The difference between means of
measured mpMRI parameters for AAs and CAs was assessed by t-test. Receiver
operating characteristic (ROC) analysis was used to evaluate the performance of
the quantitative mpMRI parameters in diagnosing PCa, and ideal cutoff point
(Youdens index) with associated sensitivity and specificity were reported.Results
AA (20% G3+3, 53%
G3+4, 27% ≥G4+3) had a greater percentage of higher Gleason grade lesions
compared to CAs (29% G3+3, 58% G3+4, 14% ≥G4+3). Despite more high grade
lesions in AA, the ADC (1.17±0.35 vs 1.06±0.34 µm2/ms, p=0.24) and T2 (109.4±21.4 vs 99.7±27.7
ms, p=0.25) for lesions in AA were nominally
higher than in CA. Cancer signal enhancement rate was significantly higher for AA
compared to CA (11.4±4.7 vs 6.1±4.7 % per s, p=0.02), while no differences in benign tissue was found (7.3±5.4
vs 5.3±3.8 % per s, p=0.28).
ROC
analysis for differentiating PCa from benign tissue shows that ADC (0.81 vs 0.87,
p=0.12) and T2 (0.72 vs 0.79, p=0.13)
are slightly (nominally) less effective in AA compared to CA, while DCE (AUC using
α: 0.73 vs 0.57, p<0.05; β: 0.80
vs 0.49, p<0.05) significantly
improved the differentiation of PCa from benign in AA. The cutoff (Youden’s
index) for quantitative mpMRI parameters were different (by >10%) for the 2
ethnicities. Discussion
This
study shows that different ethnicities: AAs and CAs have different quantitative
MRI values, specifically for DCE-MRI that affects the utility of MRI in the
diagnosis of PCa. Despite having more high grade lesions in AA, cancers in AA
tend to have nominally higher ADC and T2 values than those in CA, suggest that
cancers in AA are likely to appear as less hypointense or isointense regions
with respect to surrounding benign tissue on ADC and T2W images (dominant
sequences as per PI-RADS) and are more likely to be missed by radiologists. This
is in agreement with qualitative mpMRI results from Mahran et. al. where negative predictive value for AA using mpMRI is
lower than that for CA (5).
With
quantitative DCE-MRI using EMM, cancers and more specifically clinically
significant cancers (≥ Gleason 3+4) tends to have significantly higher signal
enhancement rate in AA vs CA, with similar rates for benign tissue in both
cohorts. Therefore, quantitative DCE-MRI can improve PCa diagnosis in AAs,
evidenced by higher AUCs in AA compared to CA.
Since,
the ideal cutoff values for quantitative mpMRI parameters were different (>10%),
the optimal thresholds for PCa diagnosis for different ethnicities using
quantitative MRI should be determined independently. If these results are
verified in a larger cohort in a multi-center setting, PI-RADS guidelines with
a larger emphasis on DCE-MRI for AAs may be recommended. We are trying to
compare these results with an Asian population, the ethnicity with the lowest
incidences of PCa. This will be step towards improved PCa diagnosis based on personalized
diagnosis.
Conclusion
This study shows that
the AA and CA have different quantitative MRI values with different thresholds needed
for PCa diagnosis. Importantly, quantitative DCE-MRI can improve PCa diagnosis
in African Americans.Acknowledgements
No acknowledgement found.References
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