Abstract
Introduction
Prostate cancer accounts for 26% of all cancer diagnoses and is the second leading cause of cancer-related deaths in American men. 1 Prostate-specific antigen (PSA) screening prior to prostate biopsy in the European Randomized Study for Screening for Prostate Cancer (ERSPC) showed a decrease in death from prostate cancer by 31%. However, the use of PSA alone as a screening tool for clinically significant (Grade Group 2 or higher) prostate cancer is controversial, given its low specificity and low positive predictive value for the detection of clinically significant prostate cancer.2,3 Prostate biopsy is an invasive diagnostic procedure with well-recognized risks including hematuria, urinary tract infections, anal bleeding, and sepsis. After undergoing biopsy, 60–70% of patient’s initial systematic prostate biopsy results are negative due to the very limited and random sampling approach associated with the standard-of-care method. 4 In addition, unnecessary prostate biopsy sessions have led to the over diagnosis of low-risk prostate cancer, which places an undue psychologic burden on patients and potential unnecessary treatments. 5 Alternatively, overtreatment of low-grade, biologically indolent prostate cancer puts patients at excessive risk for treatment-related side effects and potential complications. Therefore, there has been a strong incentive to better select men for prostate biopsy beyond the initial PSA elevation trigger.6,7
Magnetic resonance imaging (MRI) has been used for the assessment of the prostate gland since the 1980s but was largely utilized to define locoregional staging.
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In 2012, the European Society of Urogenital Radiology published guidelines for the Prostate Imaging-Reporting and Data System (PI-RADS), the standardized scoring system for prostate cancer, and has now undergone multiple version updates.8,9 Multiparametric magnetic resonance imaging (mpMRI) combines at least two functional imaging modalities that also include diffusion weighted imaging (DWI), apparent diffusion coefficient (ADC) derived from DWI sequences, and dynamic contrast enhancement to assess prostate tissue for the potential presence of malignant transformation. Several studies have demonstrated the high level of accuracy of mpMRI in the diagnosis of prostate cancer.10–13 The prostate MR imaging study (PROMIS) validated mpMRI accuracy in a multicenter, paired-cohort study with 576 men who underwent mpMRI followed by transrectal ultrasound (TRUS) and a systematic template biopsy schema. mpMRI was more sensitive in detecting clinically significant prostate cancer than TRUS systematic biopsy alone (93%
Decision-making models are commonly utilized in the management of prostate cancer. Nomograms are the most frequently utilized and allow clinicians to integrate patient data into risk and prognostic assessments to aid in clinical decision-making. Classically, nomograms have been a two-dimensional graphical device but now are generally an electronic formula on a device that inputs specific variables to provide the likelihood of the endpoint. Development of nomograms is a multi-step process that begins with the selection of a clinical question and identifying variables of potential interest. As there are an infinite number of possible variables to include in a nomogram, variables are generally derived based on established associations that have previously been postulated or proven to be clinically relevant. Once the model is established, it is validated internally to determine whether the model can usefully discriminate the outcome of interest, which is usually expressed as an area under the curve (AUC) on a receiver operating characteristic curve (ROC). Once the accuracy of the nomogram is established, thresholds for clinical decision-making can then be derived through decision-curve analyses. Finally, models should be externally validated with a population different from the testing population to confirm generalizability for wider adoption and application in clinical practices beyond the subpopulation from which the risk calculator was developed.
In this literature review, we examine how clinical decision-making models have been enhanced over time by the inclusion of mpMRI and their clinical impact on improving the diagnosis of clinically significant prostate cancer. In addition, we will review the role of nomograms on enhancing treatment plans in men diagnosed with clinically localized prostate cancer.
Nomograms in prostate cancer screening
Initial prostate biopsy nomograms were based on a study in 1994 that paired digital rectal exam (DRE) findings with serum PSA concentrations. Of the 160 volunteers who underwent radical prostatectomy (RP) and pathological staging, identification of organ-confined prostate cancer was identified in 71% of patients using PSA alone, but DRE was only able to identify 56%. This study demonstrated that combining PSA and DRE findings led to the improved identification of organ-confined disease in 78% of patients. Ultimately, the study concluded that prostate biopsy should be considered if either the PSA level is greater than 4 ng/mL or digital rectal examination is suspicious for cancer, even in the absence of abnormal TRUS findings.16,17
Studies prior to mpMRI
Early, large-scale prostate cancer screening studies used 4.0 ng/mL as the threshold for recommendation for prostate cancer biopsy; however, it was noted that men with PSA levels between 2.5 and 4.0 ng/mL had similar rates of prostate cancer.18,19 This prompted the need to find additional factors to help predict prostate cancer. In 1999, Eastham
Finne
In 2003, Garzotto
This may be due to the suggested poor ability to identify cribiform morphology Gleason pattern 4 on mpMRI. 26 Although, it has been recently shown that cribiform morphology could accurately be identified in the peripheral zone by primarily focusing upon ADC values from the DWI of the mpMRI. 27 This study highlighted the need for information in addition to mpMRI in order to determine those that should and should not be biopsied. The nomograms presented below highlight the AUC of each nomogram without specifically highlighting sensitivity or specificity as these values change with different cut-off thresholds for detection of clinically significant prostate cancers. Further work may be necessary to identify if widely accepted cut-off thresholds or individual nomogram cut-offs should be utilized to maximize utility and comparability (Table 1).
mpMRI nomograms for prostate cancer for patients that are biopsy naïve, have had previous biopsies, on active surveillance and for treatment planning.
AS, active surveillance; AUC, area under the curve; DRE, digital rectal exam; GG, grade group; ISUP, International Society of Urological Pathology; mpMRI, multiparametric magnetic resonance imaging; MRI, magnetic resonance imaging; MSKCC, Memorial Sloan Kettering Cancer Center; PIRADS, Prostate Imaging-Reporting and Data Systems; PSA, prostate-specific antigen; RP, radical prostatectomy; TRUS, transrectal ultrasound; US, ultrasound.
The table includes the study that it was published in, the patient location and number in the study used to create the nomogram, the risk factors used in the nomogram, outcomes for the nomogram, internal validation AUC and external validation AUC with corresponding study.
MpMRI nomograms
Biopsy naive
The ERSPC was used in creating an initial circular sliding nomogram utilizing PSA, prostate volume, DRE, and TRUS findings but later evolved to include seven different risk calculators for the stages of treatment for prostate cancer.
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For example, Step 3, biopsy-naive, of the ERSPC risk calculator (ERSPC-RC3) used PSA, DRE, TRUS prostate volume, and TRUS imaging abnormality to determine whether patients should be biopsied.
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This study and other validation studies suggested that this model could reduce unnecessary biopsy by 20–33%.53–59 Gayet
The first risk calculators to utilize mpMRI for the identification of clinically significant prostate cancer were created in 2017.28,30,32 ModDis, a nomogram created by Distler
Although mpMRI increased the AUC for predicting clinically significant prostate cancer, it can also lead to excessive resource utilization and costs. That is where Troung
In 2013, Hansen
Previous negative biopsy
The Prostate Cancer Prevention trial (PCPT) identified PSA, family history, abnormal DRE, and prior negative biopsy as useful predictive factors for any prostate cancer. However, PSA, abnormal DRE, older age at biopsy, previous negative biopsy, and African-American (AA) race were factors in predicting higher-grade disease (Gleason score ⩾ 7). The PCPT Risk Calculator (PCPTRC) has been updated several times over the years. In 2013, a risk calculator based on PCPT was created that now included prostate volume and AUA symptom score.
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The official PCPTRC was updated first in 2014 to include low-risk prostate cancer, and then again in 2018.66–68 The 2014 PCPT risk calculator was externally validated by the Prostate Biopsy Collaborative Group (PCGB) consisting of 25,449 biopsies from 10 international cohorts and at the Early Detection Research Network. The 2014 PCTPT was compared to the ERSPC-RC stage 4 (ERSPC-RC4, prior negative biopsy) in 2016 by Poyet
Although race had been included in previous prostate cancer risk assessments, the PCPT identified AA race as a predictor of high-grade disease. A similar simultaneous study done at several institutions in the United States analyzed 9473 patients at equal-access health care institutes created a nomogram that utilized AA race as a key predictor of prostate cancer. The nomogram utilized AA race, age, year of biopsy, PSA level, DRE, and number of cores taken to be statistically significant. The final predicted model had a concordance index of 75%. Of note, AA men in the study had significantly higher PSA levels than Caucasians. 71
The inclusion of mpMRI has been shown to vastly improve prior negative biopsy risk calculators. van Leeuwen
ERSPC-RCs were updated in 2019 to include mpMRI. Alberts
Analysis of the ERSPC screening in Sweden in 2008 and later in France in 2010 derived an algorithm for predicting prostate cancer at biopsy by combining human kallikrein-related peptidase 2 to blood-total, free, and intact PSA or the 4Kscore. Comparing PSA alone in the cohort from Sweden to the 4 K score increased the AUC from 0.608 to 0.84.72,73 Later, a 4 K nomogram based off 574 men in New York that included mpMRI found 4 K score, PI-RADS ⩾ 4, and a prior negative biopsy to be significant predictors of prostate cancer, clinically significant prostate cancer (Gleason score ⩾ 3 + 4), and unfavorable prostate cancer (Gleason score ⩾ 4 + 3). The AUC for these three were 0.84, 0.88, and 0.86 compared to 0.73, 0.80, and 0.81 for 4 K score alone. 36
A group at Stanford University created a unique nomogram that utilized mpMRI to predict clinically significant prostate cancer with a prior biopsy history using 2125 men cared for across three different institutions. The group validated the study based on data sets at two other large academic institutions. The Stanford Prostate Cancer Calculator (SPCC) used biopsy history, PSA density, PIRADS score of 4 or 5, Caucasian race, and age as risk factors. 37 The AUC of the SPCC was 0.78, 0.85, and 0.80 at the three institutions. This study also noted that AA race did not confer a higher risk for prostate cancer. However, SPCC does not include men with a normal MRI, and they did not include family history in their model. An online version of this model is available. 74
The Prospective Loyola University mpMRI (PLUM) Prostate Biopsy assessed for predictors of clinically significant prostate cancer in 900 men who were either biopsy-naive or had prior negative biopsies. Patients underwent mpMRI followed by TRUS fusion-guided biopsies with both systemic and targeted core PSA. Predictors for any cancer were found to include PSA, PSA density, prostate volume, and PI-RADS score. The study noted that family history and race were not associated with prostate cancer in the prior negative biopsy setting. The AUC for clinically significant prostate cancer of biopsy-naive patients was 0.877 with PI-RADS scoring and 0.814 without. In addition, the AUC for the prior biopsy group dropped from 0.869 to 0.775 with the removal of PI-RADS scoring. Regarding PI-RADS cut offs, for biopsy-naive patients a PI-RADS cutoff of 3 most closely approximated the model up to a threshold of 16% change of clinically significant prostate cancer. For the prior biopsy group, a PI-RADS cutoff of 4 was closest approximation up to the threshold of 27% chance of clinically significant prostate cancer. An online version of this model is also available.38,75
Active surveillance
Active surveillance (AS) provides select patients an option to delay or potentially avoid definitive treatment of their localized prostate cancer. AS protocols have generally been based on clinical parameters including PSA, clinical stage, and biopsy results. However, misassignment of patients into AS protocols that result in worse oncologic outcomes or exclusion of patients into AS protocols leading to overtreatment are all issues that continue to be active areas of debate. It has been hypothesized that the inclusion of clinically insignificant disease, Gleason 6 or Grade Group 1 (GG1) in these protocols and their use of predefined thresholds of each clinical variable, prevents an individualized assessment of a patient’s candidacy for AS.76,77 The inclusion of mpMRI and MRI-targeted biopsy has improved the prediction of upgrading Gleason score on confirmatory biopsy in men on AS.
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Therefore, Lai
Gandaglia
Luzzago
Treatment planning
The assessment of tumor extension, risk of residual disease, and determine of whether to perform a pelvic lymph node dissection (PLND) in men with newly diagnosed localized prostate cancer is critical during treatment planning. The Partin tables and D’Amico models were one of first models to risk stratify prostate cancer and predict the probability of adverse pathology and recurrence, biochemical outcomes after RP, external beam radiation therapy, or interstitial brachytherapy radiation for clinically localized prostate cancer.82–84 Since then, many nomograms have been built to assess for adverse pathologic features and lymph node invasion. 85
The decision to perform PLND concurrently at time of RP in men with localized clinically significant prostate cancer must be carefully weighed. While PLND allows accurate nodal staging and guides the potential need for adjuvant treatment, the increased operative time and complications including lymphocele and lymphedema must be considered.
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The Briganti nomogram is classically one of the most widely utilized nomograms to determine the need for PLND. Their landmark study noted 10.4% of patients having lymph node invasion at the time of surgery with PSA, Gleason score, clinical stage, and percentage of positive cores being independent predictors of lymph node invasion (
At the time of surgical resection, it is imperative to understand the presence of adverse pathologic features including extracapsular extension (ECE) and seminal vesicle invasion (SVI) as they can guide the decision to pursue sparing of the neurovascular bundle and determine the need for adjuvant treatment.92–94 The Partin tables and MSKCC nomograms have historically been used as a guide to predict the probability of ECE and SVI prior to prostatectomies; however, they do not utilize data provided by mpMRI.95,96 While mpMRI has a moderate sensitivity in predicting ECE and SVI, it has been incorporated in some models and has increased the model’s ability to predict adverse pathology.46,97–99 Soeterik
Furthermore, nomograms have been created to help in the decision to perform incremental nerve-sparing prostatectomy. Severing the neurovascular bundles during RP can lead to poor outcomes such as urinary incontinence and erectile dysfunction.100–102 Current AUA and European Association of Urology guidelines recommends against preserving the neurovascular bundle in cases with non-localized disease and the clinical stage >T2c with any biopsy Gleason score >7, respectively.103–105 Nomograms have been generated to identify patients that have ECE and are therefore excluded from nerve-sparing procedures. Ohori
Discussion
The future of nomogram use in clinical decision-making in prostate biopsies is bright. The inclusion of mpMRI findings and MRI-targeted biopsy pathology data into prostate cancer nomograms has greatly enhanced the available tools that clinicians have in weighing the decision to pursue a prostate biopsy for their patients. Online calculators such as those provided by the PCPTRC, PBCGRC, SPCC, and PLUM allow providers and their patient’s easy access to the risk assessments these models provide. However, careful consideration of the patient populations that are included in these studies and whether these studies have been extensively externally validated must be carefully weighed before utilizing them.
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Further considerations in assessing these models in younger men at risk for prostate cancer should be considered for the future as the decision to pursue active treatment
Unfortunately, nomograms need to be extensively validated, and re-calibrated to each new population.111–113 This can be costly and time-consuming. The generation of nomograms is very dependent on the population used to create the nomogram as well as the size of the population to work with. This is where a potential for national/international large database could be generated. Adding information to established online databases, could provide researchers more access to either create or externally validate their nomograms on an equal data set to enhance generation and comparisons between nomograms. In addition to validation, more studies should include cost effectiveness for incentivizing the advancements of nomograms. However, the reduced biopsy rate and potential downstream savings that result from less overtreatment offer potential cost savings that may offset the additional costs of utilizing MRI. 114 Of note, there has been no studies that survey current urologists about which nomogram they prefer to use and how often they use it. Such data could help guide more readily available nomograms, such as pre-calculated in the EMR or readily available online calculators. Nevertheless, utilizing advanced imaging, such as mpMRI, can improve the individual risk assessment, and can strengthen the shared decision-making process by well-informed patients and their clinician care providers. 115
Conclusion
Prostate cancer nomograms are simple methods of improving the accuracy of predicting clinically significant prostate cancer as compared single modality studies. There are currently many nomograms available for the physician to use. These have shown success at predicting clinically significant prostate cancer in several patient cohorts. Although, only a few of these nomograms have been externally validated. Further studies are needed to find which nomograms are the most accurate and which nomograms physician choose to use.
