1. Introduction
As of today, the prognosis of PCa at diagnosis is evaluated using classification systems designed to categorize homogeneous sets of patients [
1,
2,
3]. The two main prognostic systems for PCa are the European Association of Urology (EAU) and National Comprehensive Cancer Network (NCCN) guidelines. Even though they reference D’Amico’s risk classes, they are not entirely comparable [
1,
2]. Although parameters defining the low-risk class are consistent for NCCN and EAU, the former considers a very favorable subgroup, that less than 50% of the cores collected at biopsies are positive cores with cancer involvement not exceeding 50% of each core, clinical stage cT1c (non-palpable tumors) and PSA density (PSAD) less than 0.15 ng/mL/mL [
1,
2]. Even though the palpability of prostate tumors at presentation is an important parameter for clinical staging, palpable tumors involving both lobes of the prostate (cT2c) are categorized in the intermediate-risk class by NCCN, whereas EAU classifies such cancers as belonging to the high-risk category. However, clinical stage cT1c is included in both systems’ categories, denoting low and intermediate risk [
1,
2]. In addition, the latter considers a favorable intermediate-risk class to be a subset defined by PSA levels between 10–20 ng/mL or tumor grade group 2, according to the International Society of Urologic Pathology (ISUP) system, or clinical stage cT2b-2c and a less than 50% percentage of biopsy positive cores (BPC); nevertheless, patients may present with PSA < 10 ng/mL as well ISUP grade group 2, thus representing a very favorable subgroup, but are still included in the aforementioned group [
1,
2].
Thus, favorable low- and intermediate-risk classes are very important prognostic subgroups that promote active surveillance (AS) with eventual delayed treatment [
1,
2]. However, radical prostatectomy (RP) and radiation therapy (RT) are pursuable strategies in patients with favorable low and intermediate PCa [
1,
2]. On the other hand, the issue of tumor misclassification, particularly concerning upgrading and upstaging patterns, persists as a challenge today, with an increased risk of disease progression (which includes undifferentiated (ISUP ≥ 3) and non-organ-confined tumors) [
1,
2,
3,
4,
5,
6,
7]. Despite this, until prognostic molecular markers are integrated, there is a pressing need to improve conventional clinical predictors of disease progression in very favorable low and intermediate categories to reduce treatment-related regret [
8]. So far, early PCa may encompass highly favorable subsets within the low- and intermediate-risk categories defined by the EAU, including patients with PSA levels < 10 ng/mL, BPC < 50%, and non-palpable tumors (cT1c), but differing only in the ISUP grade group, which is 1 for the former and 2 for the latter, respectively.
In this study, we aimed to evaluate the influence of unfavorable tumor grade (ISUP grade group > 2) on PCa progression after RARP in a very favorable PCa population with low/intermediate risk-class features, presenting with PSA < 10 ng/mL, BPC < 50%, clinical stage cT1c (non-palpable tumors) and including biopsy ISUP grade groups 1 and 2. The secondary endpoint was to assess clinical and pathological predictors of unfavorable tumor grade.
4. Discussion
In the natural course of prostate cancer (PCa), biochemical recurrence following primary surgery or radiation signifies adverse oncological outcomes, preceding metastatic progression, ultimately impacting disease-specific and overall mortality. Consequently, unfavorable tumor grade in the surgical specimen serves as the primary indicator of PCa progression [
1,
2,
3]. So far, tumor grade misclassification in early PCa, including very favorable subsets of the low- and intermediate-risk classes, serves as the primary predictor of disease progression and, consequently, is a serious issue for clinicians when making treatment decisions [
1,
2,
13,
14]. The new grading group system proves to be a strong predictor of PCa progression in a large cohort of 20,845 cases. Higher-grade groups show significantly increased hazard ratios compared to grade group 1 (HR 2.2, 7.3, 12.3, and 23.9 from ISUP to 5, respectively). Grade group 2 indicates a favorable prognosis with rare metastases. However, the study does not stratify the primary endpoint based on clinical prognostic risk groups [
15].
However, adverse tumor pathology affects prognosis differently across risk groups, with better outcomes in low-risk compared to intermediate- and high-risk categories. Treatment options may involve delayed intervention for low- and favorable intermediate-risk PCa. According to the Cambridge Prognostic Group (CPG) system, the 10-year risk of death for PCa is 1.2% for low-risk disease (CPG 1) and 2.3% for favorable intermediate-risk PCa (CPG 2), including ISUP grade group 2 or PSA levels of 10–20 ng/mL and stages T1-T2. Untreated, these rates increase to 4.2% and 4.7%, respectively [
16,
17]. A recent North American study, evaluating rates of adverse surgical pathology with survival implications in favorable intermediate-risk patients compared with low-risk cases, showed that adverse pathology after RP was observed was three times more prevalent in the former group compared to the latter. Additionally, the latter group demonstrated superior overall survival [
18]. In the low- and intermediate-risk categories, a recent comprehensive literature review highlighted that unfavorable pathology affects up to 30% of cases and contributes to disease progression. Furthermore, disease progression might also be anticipated by a short PSA doubling time (PSA-DT) and high tumor grade post-surgery [
19].
In a large European cohort, a study found that a PSA-DT < 2 years and ISUP > 3 identified a high-risk group linked to metastatic progression and cancer-specific mortality. However, the study included ISUP grade group 3 in the low-risk category. Additionally, researchers suggested refining EAU BCR groups [
20]. Another multicenter study revealed that 10.6% of intermediate-risk patients had favorable pathology (ISUP grade group 1), associated with better PSA recurrence-free survival rates compared to unfavorable pathology (94.2% vs. 74.4% at 4 years) [
21]. However, this study had limitations, including a short follow-up and lack of central pathology revision.
Moreover, while salvage RARP is feasible, albeit technically challenging, after recurrence after primary treatment, including ADT, no data regarding patients with low or favorable intermediate risk who then underwent these subsequent treatments are available to assess the impact of ADT on PCa progression [
22,
23,
24,
25,
26].
Our results showed that adverse tumor grade was an independent negative prognostic factor in a highly selected population, including EAU low- and intermediate-risk classes, which closely resembled each other, in including PSA < 10 ng/mL, clinical stage cT1c, BPC < 50%, but differed only in biopsy ISUP, defined as 1 for the former and 2 for the latter. Therefore, 5-year progression rates were higher in subjects hiding adverse pathology (ISUP > 2) than in cases without, 26% vs. 8%, respectively; however, the prognostic impact was not the same among the very favorable, low- and intermediate-risk classes; accordingly, 5-year progression rates were 44% for the latter and only 13% for the former. Interestingly, pathology ISUP grade group 2 compared with group 1 did not associate with PCa progression, thus showing that its detection has no negative prognostic impact in these highly selected sets of patients. This information is important for clinicians (urologists and radiation oncologists) when counseling patients; moreover, it supports the current guidelines on recommending AS for ISUP grade group 2 (see reference literature by EAU and NCCN) [
1,
2].
Additionally, a European multicenter study investigated the impact of clinical criteria on predicting adverse disease outcomes in individuals with low and intermediate PCa risk treated with RP. Results showed that PSA levels, PSAD, tumor grade group, and tumor stage were all independent predictors of unfavorable pathology. Specifically, unfavorable pathology was observed in 17.9% of cases within the low-risk category and 44.3% in the intermediate-risk category. However, the study’s utility is limited by its inclusion criteria and lack of centralized pathology review due to its multicenter nature [
4]. In a retrospective analysis, a favorable intermediate-risk subgroup was characterized by ISUP grade 2 with PSA levels below 20 ng/mL and no more than two positive biopsy cores. Adverse pathology was detected in approximately 25% of specimens, with unfavorable tumor grade (ISUP > 2) accounting for 23.2% of cases. In addition, they showed that PSA and PSAD levels were associated with unfavorable pathology; however, biopsy ISUP 1 was not available for analysis, and they were unable to clinically identify a subgroup with adverse pathology findings with rates comparable to those of low-risk patients [
27]. Recently, a study in North America crafted and validated a nomogram forecasting adverse pathology, delineated as ISUP > 1 and/or ECE/SVI, in low-risk patients who underwent surgical intervention; the model, integrating conventional clinical factors with mpMRI findings, demonstrated an accuracy rate of 87%. However, the study faced several limitations owing to its retrospective nature, the involvement of only one high-volume surgeon, and the omission of considering the distinction between favorable and unfavorable tumor upgrading, which could potentially yield differing prognostic implications [
28].
In a very favorable subgroup of low- and intermediate-risk PCa patients treated with RP, we demonstrated that adverse tumor grade in the surgical specimen resulted in an unfavorable prognostic impact on the population and both subgroups, with the latter significantly worse than the former; as a result, adverse tumor grade rates were higher for the latter than for the former (37.8% vs. 22.5%), and the same pattern was also observed for adverse tumor stage (13.5% vs. 6.2%). Our results demonstrated that ISUP grade group 2 at biopsy was an independent clinical predictor of tumor misclassification, thus clustering the two subgroups that were closely related to each other for the remaining clinical factors; furthermore, our investigation showed that older patients and those with PSAD ≥ 0.15 ng/mL/mL were more likely to have tumor misclassification in the very low-risk subset, thus representing further parameters for stratifying subjects. Unfortunately, we were unable to identify clinical predictors of adverse tumor grade other than ISUP grade 2 in the very favorable intermediate-risk group, thus suggesting that biomolecular markers are needed to select unfavorable clusters.
Tumor misclassification poses a challenge in monitoring patients with low- and favorable intermediate-risk profiles for deferred treatment. In fact, AS exhibits rising adoption rates among intermediate-risk patients in North America, especially among the elderly, with favorable intermediate PCa risk. Furthermore, it has been shown to be a safer option for the favorable class compared to the unfavorable group, with the latter demonstrating significantly higher prostate cancer-specific mortality rates than other active treatments, including RP and radiation therapy [
29]. While individuals classified within the PCa low- and favorable intermediate-risk categories may contemplate deferred treatment strategies, it is important to note that their prognoses are not equivalent [
1,
2,
3]. Therefore, although the utilization of AS for patients with favorable intermediate-risk disease is on the rise in North America, additional follow-up and research are warranted to assess safety and efficacy [
29].
While the aforementioned EAU criteria for the favorable intermediate-risk class are very selective, NCCN criteria are less selective, due to the inclusion of all of the following intermediate-risk factors, as grade group 1 or 2, less than 50% of positive biopsy cores [
1,
2,
3]. Currently, additional clinical classification parameters are needed to improve the monitoring and management of very favorable low- and intermediate-risk patients [
6,
7,
30,
31].
In our analysis, we selected very favorable subsets of low- and intermediate-risk patients presenting in daily practice; as a result, unfavorable tumor grade is to be expected in less than one-third of patients; however, those presenting with favorable clinical parameters but ISUP 2 on biopsy were more likely to have higher unfavorable tumor upgrading (37.8% vs. 22.5%) and upstaging (13.5% vs. 6.2%) rates. This additional information may assist urologists and radiation oncologists in making informed treatment decisions when advising these specific patient subsets. Thus far, very favorable low- and intermediate-risk patients defined according to the parameters of this study, despite having criteria that elect them to AS, still have the risk of delayed treatment for both subgroups, but which is certainly more unfavorable for the latter. On the other hand, very favorable intermediate-risk patients who underwent RP and with an adverse tumor grade in the surgical specimen need close follow-up monitoring; furthermore, biochemical persistence or early biochemical recurrence may indicate disease persistence or recurrence, which needs to be investigated with more advanced imaging modalities, such as PET-PSMA, to plan appropriate treatments. Moreover, when the same patient category is treated with primary radiation, adjuvant androgen deprivation therapy should be considered to avoid biochemical recurrence, which precedes disease progression and requires more extensive investigation, such as PET-PSMA, to provide further and more appropriate treatments. Overall, beyond treatments, patients should be informed that, although they belong to very favorable categories, there is a risk of tumor-grade misclassification, which is not negligible but certainly worse for the intermediate-risk group. In the favorable low-risk category under AS, older patients presenting with PSAD ≥ 0.15 ng/mL/mL should be informed that they are at increased risk of adverse tumor grade misclassification and, consequently, at risk of delayed treatment. These are some practical examples of how this information may help physicians in clinical decision-making, but more applications may occur, especially when trying to personalize treatment even in the older patient population.
Explanations are needed to interpret our findings, which indicate that tumor misclassification served as a negative prognostic factor for disease progression and was associated with clinical factors including ISUP grade group 2, older age, and PSAD ≥ 0.15 ng/mL/mL. Theoretically, older patients, in comparison to younger individuals, are more prone to longer exposure to genetic mutation dynamics and may also have a compromised immune system, which could contribute to the development of unfavorable tumor grades. Additionally, higher PSAD levels could be associated with more aggressive and extensive tumors growing in smaller prostates. Lastly, high-grade cancer cell populations may exhibit a high-density growth pattern, potentially intensified by local stimulating factors. However, these hypotheses require verification through controlled studies.
We acknowledge several limitations in our study. Firstly, it was retrospective and conducted at a single center and included only patients who were ultimately submitted to RARP, potentially limiting the generalizability of the findings. A power analysis to determine sample-size adequacy was not conducted in this retrospective cohort study. Consequently, the study’s ability to detect significant differences may be limited. Additionally, we did not assess mpMRI and molecular/genetic tests due to their unavailability in all cases. Moreover, conducting further analyses that encompass various comorbidities could evaluate their potential impacts on cancer progression during RARP. Furthermore, overall and cancer-specific survival were not evaluated due to the limited number of events. We also did not evaluate the percentage of cancer involvement in each biopsy core and the percentage of Gleason pattern 4 in biopsy-positive cores due to data unavailability, and we were not able to centrally review all specimens at prostate biopsy. A further possible drawback in the study is that it was not possible to employ multiple pathologists to reassess the specimens in order to reduce possible grading errors.
However, our study has strengths. The primary outcome was assessed at disease progression, a robust endpoint. The follow-up length was adequate, and procedures were conducted by both low- and high-volume surgeons, minimizing bias. Lastly, all surgical specimens were evaluated by our dedicated high-volume pathologist, ensuring consistency and accuracy in pathological assessments.