Utility of Multiparametric Magnetic Resonance Imaging as a Predictor of Clinically Significant Prostate Cancer in a Sub-Saharan African Population
Mariah Kerubo Obino1, Edward Ng’ang’a Chege2, Sudhir Vinayak2, Samuel Gitau Nguku2
1Department of Radiology and Imaging, Aga Khan University Hospital, Nairobi, Kenya
2Department of Radiology and Imaging, Aga Khan University, Nairobi, Kenya
Correspondence to: Dr. Mariah Kerubo Obino; email: email@example.com
Received: 20 Aug 2021; Revised: 24 Jan 2021; Accepted: 07 Feb 2022; Available online: 26 Mar 2022
Background: Traditionally, the diagnosis of prostate cancer was based on increased prostate-specific antigen level or an abnormal digital rectal examination and confirmed histologically following biopsy. Consequently, a proportion of men without cancer or with clinically insignificant disease undergo unwarranted prostate biopsies and experience resultant complications. Pre-biopsy multiparametric magnetic resonance imaging (MP-MRI) is vital in determining those with clinically significant cancer who need biopsy and those with a negative MRI who can safely avoid unnecessary biopsy. Methods: The diagnostic accuracy of MP-MRI using transrectal ultrasound-guided biopsy as the reference test was established for 133 men who had undergone MRI and biopsy. The MRI images were reviewed and reported by two independent consultant radiologists. Clinically significant cancer was defined as Prostate Imaging Reporting and Data System score ≥3 on multiparametric MRI and Gleason score ≥3 + 4 (grade group ≥2) on histology. Results: MP-MRI of the prostate was found to have 92% sensitivity, 47.8% specificity, 86.8% negative predictive value (NPV) and 62% positive predictive value for the diagnosis of prostate cancer. Conclusion: MP-MRI has a high sensitivity and a high NPV, validating its use in pre-biopsy evaluation of men at risk of prostate cancer to safely avoid unnecessary prostate biopsy and to guide biopsy of suspicious lesions.
Keywords: MRI prostate, Prostate cancer, Clinically significant prostate cancer, Prostate Imaging Reporting and Data System (PI-RADS), Gleason score
Ann Afr Surg. 2022; 19(2): 108-115
© 2022 Author. This work is licensed under the Creative Commons Attribution 4.0 International License.
Prostate cancer is one of the most commonly diagnosed cancers among men in Africa and second most common cancer in men worldwide, with lower survival rates among men of African descent ((1–3). African men have been reported to disproportionately suffer from prostate cancer, with higher incidence, advanced stage of disease, and higher Gleason score at presentation than the rest of the world ((4,5). This is attributed to genetic differences, particularly in sub-Saharan Africa, higher poverty levels, and lower levels of screening (4–9). Wallace et al. studied the tumor biology of prostate cancer and found significant differences in the tumor immunobiology between American men of African descent and those of European descent (10).
In the recent past, there has been a shift from the traditional approach of patients with an increased prostate-specific antigen (PSA) and/or an abnormal digital rectal examination undergoing a prostate biopsy for histological confirmation to having a prostate magnetic resonance imaging (MRI) done in the first instance to determine which patient would benefit from the biopsy as well as to guide transrectal ultrasound (TRUS)-guided biopsy (11–13). Multiparametric MRI (MP-MRI) of the prostate is a useful adjunct to PSA particularly in screening. Although a PSA cutoff of 4 ng/mL has an excellent negative predictive value (NPV), it has been found to have a low positive predictive value (PPV) of 30% (14,15), since it is also usually increased in benign prostatic enlargement and prostatitis (16,17). There is no definite PSA cutoff to discriminate between clinically significant and insignificant prostate cancer(14). Consequently, men without cancer may undergo unnecessary biopsies, which are not only painful and uncomfortable but also have potential risks, including rectal bleeding, hematospermia, hematuria, infection, and the worst-case scenario is life-threatening sepsis, which occurs in 1-4% (12,18).
Non-targeted systematic core TRUS-guided biopsy may detect clinically insignificant cancer, but, more crucially, it may miss clinically significant cancer (11,12,16). This makes MP-MRI an important component in the diagnostic pathway, as it provides information on tissue anatomy, gland volume, cellularity, and contrast enhancement characteristics as well as size and location of lesions seen and evidence of extracapsular tumor extension (19,20). There is good evidence that prostate MRI detects higher-grade disease that is clinically significant and may overlook low-risk disease, which is likely to be indolent. Patients with clinically insignificant/low-risk/indolent disease undergo active surveillance, whereas those with high-risk/aggressive disease are treated with hormonal therapy, surgery, or radiotherapy depending on the stage (11). Consequently, MP-MRI performed pre-biopsy can preclude the need for biopsy if the prostate gland is normal or no suspicious lesion is seen (Prostate Imaging Reporting and Data System [PI-RADS] categories 1 and 2) (21). Meanwhile, PI-RADS category 4 and 5 lesions are suspicious and require histological confirmation of prostate cancer. Localization of the suspicious lesions by MRI followed by targeted TRUS-guided biopsy has led to better yield and detection of prostate cancer than systematic biopsy. Cognitive fusion, in particular, is helpful in resourc