Can multiparametric MRI be used in triage to avoid unnecessary prostate biopsies in some individuals and more targeted biopsies in others? According to the results of a British study published in the Lancet, the answer is yes. The authors see several advantages of such pre-selection.
Transrectal ultrasound-guided prostate biopsies (TRUS), currently performed in men with suspected prostate cancer or with elevated PSA and/or after suspicious palpation/transrectal ultrasound, may be associated with side effects such as pain, infection, or bleeding. There is also a risk of unnecessary biopsies or overdiagnosis and overtreatment. A multicenter study called PROMIS from the Division of Surgery and Interventional Science at University College London has now tested the diagnostic accuracy of this procedure compared to diagnosis with multiparametric MRI. Template prostate mapping (TPM) biopsy was used as a reference test.
Sensitivity and NPV good
Participants were 576 men without previous but with now recommended biopsy (incl. those with PSA concentrations up to 15 ng/ml within the last three months and suspicious digital-rectal examination findings [DRU]). They underwent 1.5 Tesla multiparametric MRI followed by TRUS and TPM biopsy (in a combined procedure). The individual examinations took place in each case without recourse to the results of the other diagnostic surveys, in this sense therefore blinded. A carcinoma of at least 6 mm in length (maximum cancer core length, MCCL) or from a Gleason score of ≥4 + 3 was considered clinically significant. This was true in 40%, or 230 men, of the patients studied (overall, 71%, or 408 men, had tumors in the TPM biopsy).
MRI was found to be more sensitive but less specific than TRUS biopsy for clinically relevant carcinomas. The corresponding values (MRI vs. TRUS) were:
- Sensitivity 93% (negative predictive value of 89%) vs. 48% (NPV of 74%), p<0.0001
- Specificity 41% (positive predictive value of 51%) vs. 96% (PPV of 90%), p<0.0001.
After the combined biopsy procedure, systemic urosepsis also occurred in eight cases in the study.
What do the results mean?
After MRI, 418 patients, or 73%, were suspected of having relevant carcinoma. The remaining 158 patients, or 27%, were ruled out (or defined as very low or low probability). Of these, only 17 still had significant tumor (in TPM), meaning that MRI was correct in 89%, or 141 patients. Of the 418 individuals in whom multiparametric MRI was suspected, approximately half (n=205) ultimately had no or no relevant tumor.
TRUS biopsy detected 124 clinically significant carcinomas, which was true in 111 cases in TPM. Conversely, it found non-relevant or no carcinomas in 452 individuals, where as 119 later had a relevant tumor. Consequently, one in four clinically relevant tumors is missed in TRUS biopsy.
According to this study, the MRI procedure is well suited to exclude a clinically significant tumor. According to the authors, a sequential use would be optimal, in which the biopsy would (exclusively) confirm suspicious MRI findings.
Improve detection, prevent unnecessary biopsies
Therefore, the authors suggest using the appropriate MRI in triage before an initial prostate biopsy. This could eliminate the need for (unnecessary) primary biopsy in approximately one quarter of patients. Compared with TRUS biopsy alone, multiparametric MRI in concert with TRUS biopsy simultaneously increases the detection of relevant cases (and may prevent overdiagnosis of clinically nonrelevant cases). The MRI procedure provides accurate information on carcinoma size, tissue characteristics, and connectivity to the vascular system or vascularization.
The researchers’ suggestion is thus: First exclude by MRI patients with low tumor probability, then perform TRUS biopsy in the remainder, optimally guided by the (abnormal) MRI findings.
Interpretation of imaging crucial
If the results of the study are followed, multiparametric MRI now rightly forms an important part of the overall picture in the diagnosis of prostate cancer. The quality, informative value and thus the benefit of such imaging in terms of primary screening before biopsy is mainly high in specialized centers (as happened in the PROMIS study).
Source: Ahmed HU, et al: Diagnostic accuracy of multi-parametric MRI and TRUS biopsy in prostate cancer (PROMIS): a paired validating confirmatory study. Lancet 2017 Jan 19; pii: S0140-6736(16)32401-1 [Epub ahead of print].
InFo ONCOLOGY & HEMATOLOGY 2017; 5(3): 3.
