Abstract
Gleason pattern 5 (GP5) prostatic adenocarcinoma (PC) includes distinct morphologies: undifferentiated solid pattern (US), solid and cribriform with necrosis (CN), clusters and cords (CC), and isolated single tumour cells (ISTC). The role of these patterns in the metastatic setting is still poorly understood. We conducted a case-control retrospective histological characterization of two cohorts of ISUP Grade Group 5 PC, one with nodal metastases (N1) and one without (N0), comparing GP5 sub-patterns distribution, from robot-assisted radical prostatectomies with extended lymphadenectomy diagnosed between January 2013 and February 2023. A series of PC distant metastases was also retrieved and analyzed. The different GPs and their percentage were determined in lymph nodes, primary tumours, and distant metastases. A total of 88 PC N1, 70 PC N0, and 51 distant metastases were identified. Among the N1 cohort, GP5 was documented in 28/88 nodal metastases (32%), with US and CN documented in 16/88 (18%) and 9/88 (10%) cases, respectively. Overall, 79/88 patients had ISTC/CC in primary PC, but only 11 cases (14%) developed ISTC/CC in corresponding nodal metastases (p < 0.00001). In contrast, cribriform (CR) pattern was present in 75/88 lymph nodes (87%). In distant metastases, US predominated (27/51, 53%), while ISTC/CC were detected only in 6/51 cases (12%) and as a secondary pattern. Our results might suggest the existence of an intrinsic different metastatic potential of the ISTC/CC pattern, compared with CR or US, or of extrinsic environmental factors preventing their development in metastatic settings. These findings may support reconsideration of ISTC/CC as part of GP5.
Keywords: Prostate carcinoma, Gleason score, Grade Groups, Nodal metastases, Gleason sub-patterns, Metastatic potential
Introduction
Prostate cancer (PC) recurrence remains a complex challenge in clinical management, requiring a deeper understanding of predictive factors and molecular mechanisms driving metastasis [1]. One of the most important prognostic indicators of PC is the Gleason grading system [2–4], in which Gleason pattern 5 (GP5) stands out as a marker of highly aggressive tumours with distinctive histopathological features [5, 6]. Over the last years, the International Society of Urological Pathology (ISUP) has played a major role in refining the Gleason grading system to better reflect evolving pathological and clinical insights. Modifications introduced during the 2005, 2014, and 2019 ISUP conferences improved the definition of GP5. Recent publications highlighted the surprisingly wide spectrum of architectural subtypes encompassed within GP5 [7–10]. Currently, GP5 includes distinct morphologies: undifferentiated solid (US), solid and cribriform with necrosis (CN), clusters and cords (CC), and isolated single tumour cells (ISTC). Among these, ISTC (prevalence range 50–75%) and CC (prevalence range 50–95%) frequently co-occur and are the most frequently observed at the primary site, followed by US and CN [11]. From a clinical perspective, the pathological stage on radical prostatectomy (RP) specimens—i.e. intra and extra-prostatic extension, seminal vesicle invasion, intraductal carcinoma (IDC), and particularly nodal and distant metastases—remains crucial determinants of disease recurrence [12, 13]. Notably, nodal metastases have a significant impact on patients’ prognosis [14, 15]. Over the past decade, studies exploring the histological features of lymph node metastases and their correlation with clinical data have contributed to a more comprehensive understanding of PC behaviour. Some of these features—including the number of involved lymph nodes (multiple versus single), volume of metastatic foci, and presence of extra-nodal extension—have demonstrated strong prognostic value for cancer progression and biochemical recurrence (BCR) [16]. About 5–13% of PCs are metastatic at diagnosis [17, 18] yet the mechanisms underlying disease progression remain poorly understood. Similarly, the prognostic impact of different Gleason sub-patterns within the lymph nodes is not well defined [19, 20]. It is well established, however, that higher Gleason score in primary PC correlates with an increased likelihood of dissemination to lymph nodes [21, 22]. Nevertheless, to our knowledge, no previous study has directly compared the distribution of various GP5 morphologies and sub-patterns between primary PCs and metastatic sites.
In this study, we aimed to compare the distribution of GP5 sub-patterns between a cohort of ISUP Grade Group 5 primary PCs without lymph node involvement and a cohort with nodal metastases. Additionally, we characterized the different sub-patterns in a series of prostatic distant metastatic lesions.
Materials and methods
Case selection
This retrospective monocentric study was submitted to the Internal Ethics Committee of Humanitas Research Hospital (Milan IT) for approval (prot.n° APA-2025-01). From the archives of the Pathology Department, all ISUP 5 PC cases from RP with extended lymphadenectomy diagnosed between January 2013 and February 2023 were retrieved. Cases without available histological material were excluded. After histological revision by two expert uropathologists, tumours with a histotype other than prostatic acinar adenocarcinoma (i.e. neuroendocrine, ductal adenocarcinoma), incorrect ISUP classification, or those showing cyto-architectural changes due to prior systemic or hormonal treatment were excluded from the study. Two cohorts of patients were identified according to nodal status (N0 and N1). Additionally, a series of distant metastases from prostatic carcinoma (M1) specimens was retrieved.
Morphological assessment of Gleason patterns
All slides were reviewed independently by two uropathologists, and cases with discordant results were discussed to reach consensus. For primary tumours of both N0 and N1 cohorts, GP5 sub-patterns (ISTC, CC, US, and CN) were identified and recorded as present or absent. GP5 sub-patterns were divided as follows: tumour composed of discrete small clusters or cords and “Indian files” of tumour cells without glandular formation, sometimes with hyperchromasia and atypical nuclei, was classified CC; isolated single cells were classified ISTC; tumour composed of solid sheets and nests was classified US; lastly, solid nests or cribriform structures with comedonecrosis were classified CN. GP4 was quantified as a percentage, as well as the presence of cribriform morphology (CR). GP CR was defined as the presence of a confluent sheet of cells forming glandular structures with multiple, punched-out lumina that are not separated by intervening stroma. GP4 CR was classified as small or large (the latter defined as at least twice the size of adjacent benign glands) [23]. Intraductal carcinoma was diagnosed histologically when unequivocal based on 2022 WHO criteria; due to morphological overlapping between invasive cribriform adenocarcinoma and IDC, immunohistochemical evaluation for basal cells (CK34βE12 and p63) was performed in a subset of cases. For nodal and distant metastases, GPs were recorded as percentage and categorized as primary, secondary, or tertiary. In case of multiple positive lymph nodes, an overall evaluation was performed. Specific sub-patterns of GP5 were recorded (ISTC, CC, US, and CN for GP5); for GP4, a distinction between cribriform (CR) and non-cribriform (NCR) patterns was made. Other clinico-pathological characteristics were assessed and recorded for both primary tumours—i.e. age at surgery, pTNM, tumour volume, lympho-vascular invasion (LVI), and concomitant IDC—and nodal metastases—i.e. number of positive lymph nodes and topographical distribution (parenchymal, subcapsular, capsular). Tumour volume was calculated as a percentage for each slide; the sum of the percentages was divided by the total number of slides.
Statistical analysis
Patient characteristics were reported as descriptive statistics. Pearson’s chi-squared test and Wilcoxon’s rank sum test were used to compare categorical and continuous variables, respectively. A two-sided p-value (p) < 0.05 was considered statistically significant. All analyses were performed using STATA version 17.0 (StataCorp, College Station, TX, USA).
Results
The cohort consisted of a consecutive series of 3555 patients undergoing RP with lymphadenectomy for PC between January 2013 and February 2023, from which we identified a total of 270 primary ISUP GG5 PC cases. Among these, patients were excluded due to incomplete or inadequate histologic material (62 pts), previous systemic or local treatment (36 pts), or histologic subtype different from acinar adenocarcinoma (2 neuroendocrine neoplasms and 2 ductal adenocarcinomas); furthermore, due to the interobserver variability and overlapping features between ISTC/CC and poorly formed gland GP4, we reclassified ISUP grading in 10 pts from ISUP GG5 to GG4. Overall, 88 pN1 and 70 pN0 PC cases were included in the study.
Evaluation of primary PC N0 patients
Clinico-pathological characteristics of 70 PC N0 pts are summarized in Table 1. The median patient age at surgery was 67 years (IQR 63–71). Tumour staging was as follows: pT2 in 15 pts (21%), pT3a in 28 pts (40%), pT3b in 26 pts (37%), and pT4 in one patient. Most tumours (77%) were pT3a-pT3b. Tumour volume ranged from 3 to 85% (median 24%, IQR 15–36.5). The Gleason score distribution was as follows: 80% (56/70) GS 4 + 5, 19% (13/70) GS 5 + 4, and 1 case (1.4%) GS 5 + 5. Among GS 4 + 5 and 5 + 4 tumours, the percentage of GP4 ranged from 10 to 90% (median of 70%, IQR 60–80). Invasive CR morphology was present in 69% of GP4 cases (48/70). Regarding GP5 sub-patterns, CC was observed in 62/70 cases (89%), followed by ISTC in 38/70 (54%). US was present in 35/70 cases (50%), while CN was identified in 18/70 cases (26%). IDC was present in 33% (23/70), and LVI in 9% (6/70) of cases.
Table 1.
Primary tumour characteristics, N0 and N1 series
| Variable | N0 (n= 70) | N1 (n= 88) | p-value | |
|---|---|---|---|---|
| Age, y, median (IQR) | 67 (63-71) | 69 (63-72) | ||
| pT, No. (%) | <0.001 | |||
| 2 | 15 (21) | 0 (0) | ||
| 3a | 28 (40) | 13 (15) | ||
| 3b | 26 (37) | 73 (83) | ||
| 4 | 1 (1) | 2 (2) | ||
| Tumor volume, %, median (IQR) | 24 (15-36,5) | 40 (25-60) | <0.001 | |
| GS, No. (%) | 0.2019 | |||
| 4+5 | 56 (80) | 74 (84) | ||
| 5+4 | 13 (19) | 10 (11) | ||
| 5+5 | 1 (1) | 4 (5) | ||
| Percentage of GP4, %, median (IQR) | 70 (60-80) | 65 (50-80) | ||
| Cribriform component, No. (%) | ||||
| Yes | 48 (69) | 79 (90) | 0.00086 | |
| No | 22 (31) | 9 (10) | ||
| Large | 23 (48) | 58 (73) | <0.001 | |
| Small | 36 (75) | 45 (57) | ||
| GP5 sub-patterns, No. (%) | 0.791 | |||
| ISTC | 38 (54) | 41 (47) | ||
| CC | 62 (89) | 75 (85) | ||
| ISTC/CC | 65 (93) | 79 (90) | ||
| US | 35 (50) | 41 (47) | ||
| CN | 18 (26) | 31 (35) | ||
| Intraductal carcinoma, No. (%) | 0.277 | |||
| Yes | 23 (33) | 22 (25) | ||
| No | 47 (67) | 66 (75) | ||
| LVI, No. (%) | <0.001 | |||
| Yes | 6 (9) | 66 (75) | ||
| No | 64 (91) | 22 (25) | ||
IQR interquartile range, GS Gleason score, GP Gleason pattern, ISTC isolated single tumor cells, CC clusters and cords, US undifferentiated solid, CN cribriform/solid with necrosis, LVI lymphovascular invasion
Evaluation of primary PC N1 patients
Clinico-pathological characteristics of 88 PC N1 patients are summarized in Table 1. The median age at surgery was 69 years (IQR 63–72). Overall, 13/88 tumours were pT3a, while the majority (83%) were pT3b. Tumour volume ranged from 5 to 95% (median of 40%, IQR 25–60). Gleason scores included 84% (74/88) GS 4 + 5, 11% (10/88) GS 5 + 4, and 5% (4/88) GS 5 + 5 cases. CR morphology was documented in almost all cases (94%). Among GP5 sub-patterns, CC was the most represented (75/88 cases; 85%). ISTC and US were equally distributed (both 47%; 41/88 patients), while CN was present in 35% (31/88) of cases. IDC was detected in 22/88 tumours (25%), and LVI in 66/88 (75%) of cases.
Morphological features of nodal metastases are summarized in Table 2. The number of lymph node metastases ranged from 1 to 6, with 50% of cases having multiple positive nodes (44/88). About half of nodal metastases showed multiple GPs (51%), with a predominance of GP4 over GP5 in 76% of cases. Only one case presented GP5 as an exclusive pattern, and one case showed GP3 as a secondary pattern. GP4 was found in 99% of cases (87/88), 87% of which showed CR. Conversely, GP5 was present only in 28/88 patients (32%); among these, 16/28 cases displayed US, 9 cases showed CN, 5 ISTC, 5 CC, and 1 patient presented both ISTC and CC. ISTC and CC, taken together, were uncommon in metastases, found in only 11/88 cases (12.5%). GP4-CR was the primary pattern in 66% of cases (58/88). Among GP5 sub-patterns, US was the primary in 50% of cases (8/16) and secondary pattern in remaining cases. GP5-CN was primary in 2 cases, secondary in 4, and tertiary in 3; CC was primary in 2 patients, secondary in 3, and tertiary in 1; ISTC was never the primary pattern, while secondary in 2 and tertiary in 4 cases. The most frequent sub-pattern association was GP5-US and GP4-CR in 13 cases. The presence of ISTC/CC did not correlate with the number of metastatic lymph nodes (p > 0.05). GP5 sub-patterns were not correlated with the topographical distribution of metastases in lymph nodes (p > 0.05).
Table 2.
Nodal metastases characteristics
| Variable | Cases (n = 88) | |
|---|---|---|
| Number of positive lymph nodes, No. (%) | ||
| 1 | 44 (50) | |
| > 1 | 44 (50) | |
| Location, No. (%) | ||
| Extracapsular (E) | 51 (58) | |
| Subcapsular (S) | 10 (11) | |
| Parenchymal (P) | 53 (60) | |
| E + S | 2 (2) | |
| E + P | 19 (22) | |
| S + P | 3 (3) | |
| GP3, No. (%) | 1 (1) | |
| GP4, No. (%) | ||
| Total | 87 (99)* | |
| Cribriform | 75 (87) | |
| Other patterns | 29 (34) | |
| GP5, No. (%) | ||
| Total | 28 (32)* | |
| ISTC | 6 (21) | |
| CC | 6 (21) | |
| US | 16 (57) | |
| CN | 9 (32) | |
| Distribution of GP, No. (%) | ||
| Single GP | 43 (49) | |
| 4 | 42 (98) | |
| 5 | 1 (2) | |
| Multiple GP | 45 (51) | |
| Dominant 4 | 34 (76) | |
| Dominant 5 | 11 (24) | |
GP Gleason pattern, ISTC isolated single tumour cells, CC clusters and cords, US undifferentiated solid, CN cribriform/solid with necrosis, LVI lymphovascular invasion
*The sum of the numbers may not equal the total because a subset of patients presents more than one variable at a time
Comparison between PC N0 patients and PC N1 patients
As shown in Table 1, although pT3 was more common in the N0 group (with pT3a and pT3b equally distributed), N1 tumours more frequently presented with a significantly higher stage (pT3b; p < 0.001). Interestingly, GP4-CR was also more frequently documented in N1 versus N0 pts (90% vs. 69%; p < 0.001), with large CR structures being significantly more common in the N1 cases (p < 0.001). As expected, LVI strongly correlated with nodal involvement, being present in 66/88 N1 cases (75%) and only 6/70 N0 cases (9%) (p < 0.001). CC was the most common GP5 sub-pattern in both primary tumour groups; no significant differences were found among the remaining GP5 sub-patterns (p > 0.05). There was no statistically significant difference between PC N0 and PC N1 cases regarding age, tumour volume, GP4 percentage, Gleason score distribution, and presence of IDC (p > 0.05).
Comparison between primary PC cases and corresponding nodal metastases (N1)
A morphological comparison of ISUP GG5 sub-patterns between N1 primary PC and corresponding nodal metastases is depicted in Figs. 1 and 2. Among 79 of 88 patients harbouring ISTC/CC in primary PC, only 11 cases (14%) retained these patterns in nodal metastases (p < 0.001). Notably, none of the remaining 9 patients without ISTC/CC in the primary tumour showed isolated cells or clusters in the corresponding lymph node metastases. GP4-CR was frequently found in metastases regardless of its presence in the primary tumour: indeed, it was identified in nodal metastases of 67 out of 79 patients with CR in the primary tumour (85%) and in 8 of 9 patients lacking CR in the primary lesion (89%) (p > 0.05). Interestingly, two pure GS 5 + 5 tumours exhibited GP4-CR in nodal metastases. Of 22 primary PC with an IDC component, 19 (86%) showed CR in nodal metastases, whereas ITSC/CC was observed in only 7 cases (32%) (p = 0.0025). Only 5 patients in our cohort entirely lacked cribriform, solid, or IDC components in the primary tumour; nevertheless, all displayed ISTC/CC. Among these, CC was observed in a single case, whereas a cribriform pattern was identified in nodal metastases in 4 out of 5 cases.
Fig. 1.
Morphological comparison between primary prostate cancers (PC) and metastatic lymph nodes, Haematoxylin & Eosin. A, B Primary PC and corresponding nodal deposit showing isolated single tumour cells (ISTC) sub-pattern (×20); C cribriform (CR) sub-pattern in a primary PC comprising both small and large structures (×10); D same case showing CR in the metastatic lymph node (×5)
Fig. 2.
Morphological comparison between primary prostate cancers (PC) and metastatic lymph nodes, Haematoxylin & Eosin. A, B This patient presented cribriform architecture (CR) as a prevalent pattern in the prostate and developed ISTC/clusters and cords (ISTC/CC) in nodal sites (×10, ×20); C, D conversely, this primary tumour was characterized by the presence of ISTC, but the nodal metastasis showed CR as the primary architecture (×20, ×5)
Morphological analysis of samples from distant metastases
The pathological features of distant metastatic cases are summarized in Table 3. In total, 51 pts were selected from our Pathology archives between January 2013 and December 2023 for comparative analysis. ISUP Grade Groups of primary tumours were distributed as follows: ISUP GG2 in 8 patients, ISUP GG3 in 4, ISUP GG4 in 15, and ISUP GG5 in 24. Histologically, metastatic samples were predominantly composed of GP5 US (27/51 cases; 53%), followed by GP4-CR (16/51 cases; 31,4%). GP5 ISTC was rare (6/51 cases, 11,8%) and was never the dominant/primary pattern, always associated with US. Specifically, among the 6 ISTC/CC, 4 were associated with an ISUP GG5 primary PC, 1 with ISUP GG4, and 1 with ISUP GG3. The distribution of patterns by metastatic sites is detailed in Table 4. As expected, bone was the most involved site (17/51 pts), followed by lung, abdominal organs (mainly liver), and non-regional lymph nodes. Bone and abdominal metastases predominantly exhibited the GP5 pattern (12/51 and 10/51 cases, respectively) with GP4 less frequently observed (5/51 and 1/51). Among ISUP GG5 sub-patterns, US was the most frequently documented (23/51; 45%), mainly in visceral organs, followed by bone, lung, and lymph nodes. ISTC/CC was found in six patients: three in bone metastases and one each in lung, lymph node, and skin. Examples of sub-patterns across various metastatic sites are shown in Fig. 3.
Table 3.
Gleason patterns of distant metastases in the different GGs
| Primary GG | No | Patterns in metastatic deposits | |||||
|---|---|---|---|---|---|---|---|
| GP4 CR |
GP4 NCR |
GP5 US |
GP5 CN |
GP5 ISTC |
GP5 CC |
||
| GG 2 | 8 | 3 | 3 | 2 | 0 | 0 | 0 |
| GG 3 | 4 | 2 | 0 | 1 | 1 | 0 | *1 |
| GG 4 | 15 | 7 | 0 | 8 | 0 | *1 | 0 |
| GG 5 | 24 | 4 | 1 | 16 | 3 | *1 | *3 |
| Tot | 51 | 16 | 4 | 27 | 4 | *2 | *4 |
GG Grade Group, GP Gleason pattern, ISTC isolated single tumour cells, CC clusters and cords, US undifferentiated solid, CN cribriform/solid with necrosis, CR cribriform, NCR non cribriform
*Sub-pattern presents as secondary pattern and in association to US
Table 4.
Distribution of GP4 and GP5 with sub-patterns stratified by metastatic sites
| GP and sub-patterns | Lung | Bone | Lymph nodes | Abd organs | Skin | Tot (n = 51) |
|---|---|---|---|---|---|---|
| GP4 | 8 | 5 | 6 | 1 | 0 | 20 |
| CR | 5 | 4 | 6 | 1 | 0 | 16 |
| NCR | 3 | 1 | 0 | 0 | 0 | 4 |
| GP5 | 5 | 12 | 3 | 10 | 1 | 31 |
| ISTC | 0 | 1 | 0 | 0 | 1 | *2 |
| CC | 1 | 2 | 1 | 0 | 0 | *4 |
| US | 4 | 11 | 2 | 9 | 1 | 27 |
| CN | 1 | 1 | 1 | 1 | 0 | 4 |
| Tot | 13 | 17 | 9 | 11 | 1 |
GG Grade Group, GP Gleason pattern, ISTC isolated single tumour cells, CC clusters and cords, US undifferentiated solid, CN cribriform/solid with necrosis, CR cribriform, NCR non cribriform
*Sub-pattern presents as secondary pattern and in association to US
Fig. 3.
Examples of sub-patterns in different metastatic sites, Haematoxylin & Eosin (×20). A An uncommon solid and isolated cells (ISTC) vertebral metastasis in previous ISUP GG4 cribriform (CR) prostate carcinoma (PC); B tibial lesion characterized by a CR interlamellar proliferation; C pure CR metastatic deposit to the lung in a previous pT3aN1 PC; D pulmonary metastasis composed of fused glands from an ISUP GG2 primary PC; E this nodule was detected during follow up in the abdominal wall of a patient undergoing radical prostatectomy in 2012, consistent with pure solid GP5. F Mediastinal lymph node diffusely positive for CR with necrosis GP5
Discussion
A correlation between the presence of GP5 in nodal metastasis and disease-free survival (DFS) and disease-specific survival (DSS) has recently been documented, although differences in GP5 sub-patterns were not considered [22]. Among the four identified sub-patterns, ISTC and CC are the most prevalent and frequently co-occur [11]. In 2013, nodal metastases have been associated with higher volumes of cribriform (CR) and poorly formed GP4 morphologies in the primary GS7 ISUP GG2-3 tumours [24]. Nevertheless, to the best of our knowledge, no study has directly compared the distribution of various sub-patterns between primary PCs and metastases to explore their different metastatic potential or ability to reproduce specific growth patterns [19, 20].
In the present study, we conducted, for the first time, a comprehensive analysis and detailed histological characterization of ISUP GG5 prostatic acinar adenocarcinomas to better understand the biological relevance of different GP5 sub-patterns in both nodal and distant metastases.
Interestingly, CC and ISTC were equally distributed between N0 and N1 primary PC, suggesting that their presence in the primary tumour does not predict the development of these patterns in nodal metastases.
On the contrary, GP4—particularly the CR pattern—has been associated with a higher likelihood of developing loco-regional and distant metastases during follow-up [23, 25–28]. Accordingly, in 2019, both ISUP and GUPS recommended reporting the percentage of GP4 and CR pattern in prostate biopsies with GS 7 (ISUP GG2 and 3) [9, 10]. However, the prognostic impact of CR in higher-risk groups such as ISUP GG4 and 5 remains unclear. A recent paper by Martini et al., focusing on ISUP GG4 PCs, demonstrated that patients with GS 3 + 5 had a better prognosis than those with GS 4 + 4, and that tumour architecture (IDC and/or CR) was the only significant predictor of biochemical recurrence [29]. These findings suggest that GP4 morphology may have a greater prognostic influence than GP5. Most nodal deposits showed GP4 pattern, with CR being the predominant feature. Indeed, in the five cases completely and simultaneously lacking unfavourable histology like the cribriform, solid, or IDC pattern (Gleason score 5+ 4 in four cases and 4 + 5 in one case) and with ISTC/CC features in the primary tumour, unexpectedly, only one showed CC while 4/5 patients had cribriform pattern in nodal metastases. This suggests that PCs may be less capable of developing ISTC/CC in regional lymph nodes and more inclined to form CR architecture—even in the absence of GP4 CR, large or small, and other high-risk histological features in the primary tumour. As recently stated by some authors, unfavourable histology includes specific architectural patterns not classified as large cribriform or IDC by consensus definitions [30]. The cribriform pattern was strongly associated with the presence of lymph node metastases in our cases; in particular, large CR was more frequently observed in the N1 cohort compared to N0 (73% vs. 48%; p < 0.001). This finding is consistent with reports from several authors who suggest that large CR and IDC are the histologic features with the greatest impact on the risk of developing loco-regional and distant metastases [31]. Also, when examining the histological features of distant metastases, most cases showed US or CR growth pattern. Only 6 of 51 patients harboured ISTC/CC (half into the bone), always as a minor component and consistently co-occurring with US. Interestingly, although deposits in abdominal organs consisted almost exclusively of GP5, none contained ISTC/CC.
Our data show that GP5 morphology in nodal and distant metastases is relatively uncommon, particularly the ISTC/CC sub-patterns, despite ISTC/CC being found in nearly all (90%) primary PC in our cohort and being considered an aggressive morphology.
Our findings may indicate distinct metastatic potentials among specific adenocarcinoma clones, with CR clones demonstrating a greater propensity to infiltrate regional lymphatic vessels compared to ISTC/CC. Nonetheless, this interpretation remains hypothetical, as it is derived exclusively from morphological observations without corroborative molecular data. It is also possible that such morphological assessment does not adequately reflect the biological aggressiveness of ISTC/CC. Alternatively, the absence of nodal involvement by ISTC/CC may be influenced by intrinsic tumour features or microenvironmental factors that hinder the survival and dissemination of neoplastic clones as isolated cells or small clusters in lymphatic or distant metastatic niches. While cribriform pattern and IDC are known harbouring a constellation of genomic instability, SChLAP1 expression, and activation of genes related to hypoxia, no data are currently available for ISTC/CC [32].
In our cohort, the presence of nodal ISTC/CC did not correlate with GP4, CR, or IDC in the primary tumour (p > 0.05), suggesting that these patterns may arise from distinct neoplastic clones with independent oncogenic pathways. Notably, a recent three-dimensional analysis using confocal laser scanning microscopy on 46 radical prostatectomy tissue samples revealed the presence of two principal architectural subgroups: a tubular interconnecting network and a serpentine, contiguous epithelial proliferation. The former encompassed GP3, poorly formed and fused GP4, and cords of GP5, while the latter would comprise CR-GP4 and solid GP5 patterns [33]. Assuming that these findings are valid, ISTC/CC might align more closely with GP3 rather than the architectural group containing solid GP5 and CR-GP4. This could explain the lower metastatic potential of ISTC/CC compared to CR-GP4 observed in our cohort. Moreover, in nodal metastases, we noticed a tight association between CR and US patterns.
The present study is not devoid of limitations. Although the entire prostate gland was submitted for pathological evaluation in all cases within our cohorts, the analysis was based solely on the revision of routine diagnostic slides. For this reason, the accuracy of these findings may be limited by the absence of serial sectioning of tissue blocks, which could have resulted in missing small foci of different sub-patterns in the primary PC. Furthermore, there are known issues related to interobserver reproducibility in the identification of ISTC/CC and the distinction from GP4 poorly formed or fused glands [34]. Importantly, stratification by individual sub-patterns was unattainable due to the frequent and invariable commixture of multiple sub-patterns within tumour; this prevented us from providing reliable prognostic data on the impact of each specific architectural pattern. Moreover, the small number of cases showing ISTC/CC sub-patterns in lymph nodes hindered meaningful survival analysis.
Conclusions
To the best of our knowledge, this is the first study to offer a comprehensive analysis and detailed histological description of distinct GP5 sub-patterns in both nodal and distant metastases from prostatic adenocarcinoma. Moreover, we demonstrated that isolated single tumour cells (ISTC) and clusters and cords (CC) patterns are infrequently detected not only in regional nodal metastases but also in distant metastatic sites. We also confirmed that GP4 cribriform (CR) pattern represents the most commonly observed neoplastic architecture, even in cases where CR is not clearly identified in the primary tumour.
Our observations could reflect intrinsic differences in the metastatic potential of ISCT/CC clones or be influenced by still-unknown factors that prevent their development in nodal and metastatic microenvironments (tumour-intrinsic features or environmental factors such as immune system). This process may be modulated on a genomic level, which deserves further investigation.
In conclusion, if validated in future analyses with larger cohorts, our findings may support reconsideration of ISTC/CC patterns as part of Gleason pattern 5, with a downgrading, potentially contributing to a refinement of the Gleason grading categories and Grade Groups in the WHO classification of prostate adenocarcinoma.
Acknowledgements
The publication fee for this work was covered by the Italian Ministry of Health’s 'Ricerca Corrente' funding to IRCCS Humanitas Research Hospital.
Author contributions
Conceptualization: Piergiuseppe Colombo, Marina Valeri; methodology: Piergiuseppe Colombo, Marina Valeri, Miriam Cieri; formal analysis and investigation: Marina Valeri, Miriam Cieri, Matilde Pittarello, Vincenzo Belsito, Alessandra Bressan, Vittorio Fasulo; writing—original draft preparation: Marina Valeri, Piergiuseppe Colombo; writing—review and editing: Piergiuseppe Colombo, Miriam Cieri, Matilde Pittarello, Alessia Cimadamore, Grazia Maria Elefante, Giovanni Lughezzani, Nicolò M. Buffi; supervision: Piergiuseppe Colombo, Luigi M Terracciano, Rodolfo Hurle.
Data Availability
De-identified data that support the findings of this study will be provided on adeguate request.
Declarations
Competing interests
The authors declare no competing interests.
Footnotes
The study has been in part presented at the ECP (European Congress of Pathology) in 2021.
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
De-identified data that support the findings of this study will be provided on adeguate request.