1. Introduction
In 2018 was prostate cancer with more than 350,000 deaths worldwide, the second most common cause for cancer-related death in men [ 1 ]. However, many more men got diagnosed with prostate cancer [ 2 ]. It is pivotal to properly assess the patient's individual risk of tumor progression to restrict aggressive treatment to avoid treatment-related complications and affection of the quality of life [ 3 – 5 ]. The established prognostic factors (Gleason grade, tumor quantity in biopsies, prostate-specific antigen (PSA) serum values, and clinical stage) are statistically powerful but do not allow clear-cut risk stratification. Therefore, the search for novel biomarkers to improve the assessment of tumor aggressiveness goes on.
CD138 or syndecan-1 ( SDC1 ) is a transmembrane heparin sulfate proteoglycan. Its extracellular domain binds heparin sulfates and chondroitin sulfates [ 6 ]. CD138 plays an important role for cell-cell and cell-matrix interactions. It is involved in the regulation of cell migration and the organization of the cytoskeleton [ 6 ]. In normal tissues, CD138 is expressed on plasma cells and various epithelial cells. Altered expression of CD138 has been described for many neoplasias including cancers of the breast, urinary bladder, pancreas, ovary, and endometrium [ 6 – 10 ]. In several of these tumors, an increased or decreased CD138 expression was found to be linked to unfavorable tumor phenotype and poor patient prognosis [ 8 , 9 , 11 ]. The CD138 expression in cancer is also of clinical interest because specific drugs targeting CD138 are currently being evaluated in clinical trials on multiple myeloma and breast cancer [ 12 – 14 ].
The available data suggest that the increased CD138 expression may also be linked to prostate cancer aggressiveness. Although most of the 15 studies analyzing 18-551 prostate cancers have described associations of the altered CD138 expression with high Gleason grade, high Ki67 labeling index (Ki67LI), early recurrence, tumor-specific survival or elevated expression in hormone-refractory recurrences, and distant metastasis [ 15 – 28 ], there is still no consent on the suitability of CD138 as routine diagnostic marker.
On a genetic level, about 50% of prostate cancer is characterized by gene fusion of the androgen responsive TMPRSS2 serin protease and the ETS-family transcription factor ERG. Other frequent chromosomal alterations include deletions of the PTEN tumor suppressor and other loci including chromosomes 3p, 5q, 8p, 12p, 12q, 13q, 17p, and 18q, most of which are linked to either ERG fusion positive or ERG negative cancers [ 29 ]. Here, we took the advantage of a very large preexisting tissue microarray (TMA) containing more than 17,000 prostate cancer specimens to stratify the immunohistochemical CD138 expression for multiple clinical, phenotypic, and genetic parameters.
2. Materials and Methods
2.1. Patients
The 17,747 patients had radical prostatectomy between 1992 and 2015 (Department of Urology and the Martini Clinic at the University Medical Center Hamburg-Eppendorf). Prostate specimens were analyzed according to a standard procedure for tumor stage, Gleason grade, nodal stage, and resection margin status [ 30 ]. In addition to the classical Gleason categories, “quantitative” Gleason grading was performed as described before [ 31 ]. Gleason 3+4 and 4+3 cancers were divided into 8 subgroups according to their percentage of Gleason 4 pattern (3 + 4 ≤ 5% Gleason 4, 3+4 6-10%, 3+4 11-20%, 3+4 21-30%, 3+4 31-49%, 4+3 50-60%, 4+3 61-80%, and 4 + 3 > 80% Gleason 4). Two additional groups were defined by the presence of a tertiary Gleason 5 pattern (3+4 Tert.5 and 4+3 Tert.5). Follow-up was available for 14,464 patients (median follow-up 48 months, Table 1 ). PSA recurrence was defined as the time point when postoperative PSA was at least 0.2 ng/ml and increasing at subsequent measurements. The TMA was produced with one 0.6 mm core taken from a tumor containing tissue block from each patient as described before [ 32 ]. The attached molecular database contained data on Ki67LI of 5,492 tumors [ 33 ], ERG expression data of 13,089 tumors [ 34 ], ERG break apart FISH data of 7,225 (expanded from [ 34 ]), and androgen receptor (AR) expression data of 7,971 cancers [ 35 ] as well as data on the deletion status of 5q21 ( CHD1 ) of 8,047 (expanded from [ 36 ]), 6q15 ( MAP3K7 ) of 6,171 (expanded from [ 37 ]), PTEN (10q23) of 6,803 (expanded from [ 38 ]), 3p13 ( FOXP1 ) of 7,201 (expanded from [ 39 ]), 13q14 of 7,499 [ 40 ], 18q21 of 7,032 [ 41 ], 8p21 of 7,001 [ 42 ], 12p13 of 6,187 [ 43 ], 12q24 of 7,435 [ 34 ], 16q24 of 5,493 [ 44 ], and 17p13 ( TP53 ) of 8,307 cancers [ 45 ]. Archived diagnostic leftover tissues for manufacturing of tissue microarrays and their analysis for research purposes as well as patient data analysis have been approved by local laws (HmbKHG §12,1) and by the local ethics committee (Ethics commission Hamburg, WF-049/09). All work has been carried out in compliance with the Helsinki Declaration.
2.2. Immunohistochemistry
Freshly cut TMA sections were stained in a single experiment. Slides were deparaffinized and exposed to antigen retrieval for 5 minutes at 121°C in pH 9 Dako Target Retrieval Solution buffer. Primary antibody specific for total Syndecan-1 (mouse monoclonal antibody, clone JASY1, OncoDianova, dilution 1 : 200) was applied at 37°C for 60 minutes. Bound antibody was visualized with the EnVision Kit (Dako, Glostrup, Denmark). Membranous and cytoplasmic CD138 staining of variable intensity was seen in prostate cancer cells whereas no stromal CD138 staining was observed. Therefore, the percentage of positive cells and the staining intensity were separately evaluated for membranous and cytoplasmic staining. Intensity was quantitated as 0 (negative), 1+ (weak), 2+ (moderate), and 3+ (strong). The results of both membranous and cytoplasmic CD138 staining were then further categorized in 4 groups for statistical analyses. Tumors without any staining were considered as negative. Tumors with 1+ staining intensity in ≤70% of cells and 2+ intensity in ≤30% of cells were considered weakly positive. Tumors with 1+ staining intensity in >70% of cells, 2+ intensity in 31% to 70%, or 3+ intensity in ≤30% were considered moderately positive. Tumors with 2+ intensity in >70% or 3+ intensity in >30% of cells were considered strongly positive.
2.3. Statistics
The JMP® 10.0.2 software (SAS Institute Inc., NC, USA) was used. Contingency tables and the chi 2 test were done to look for associations. Kaplan-Meier plots were tested with the log-rank test for differences between groups. Cox proportional hazards regression analysis was performed to test the statistical independence and significance between pathological, molecular, and clinical variables. When indicated, Bonferroni correction was applied for multiple testing.
3. Results
3.1. CD138 Expression in Normal and Cancerous Prostate Tissues
A total of 12,851 (72%) tumor samples were interpretable in our TMA analysis. Noninformative cases ( n = 4,896; 28%) were caused by lack of tissue or unequivocal tumor cells in the corresponding tumor spot. In normal prostate tissue, basal cells showed a reproducible positive CD138 expression while no staining was detected in glandular cells. In prostate cancer, membranous and/or cytoplasmic CD138 staining was sometimes seen. Cytoplasmic staining appeared as diffuse staining of the entire cytosol, typically in addition to membrane staining. Membranous CD138 expression was seen in 19.6% of cancers from which 9.0% showed weak, 8.3% with moderate, and 2.2% with strong staining. Cytoplasmic CD138 staining was found in 11.2% of 12,851 cancers and was considered weak in 9.5%, moderate in 1.6%, and strong in 0.1%. Examples of CD138 immunostainings are shown in Figure 1 . A comparison with tumor phenotype revealed that in particular cytoplasmic CD138 staining was linked to unfavorable tumor features ( Table 2 ) and PSA recurrence ( Figure 2 ). Presence of membranous staining was also associated with unfavorable tumor phenotype and early PSA recurrence, but these relationships were less striking ( Table 3 ; Figure 3 ). Membranous and cytoplasmic CD138 staining was related. The frequency of cytoplasmic staining increased gradually from 6.1% in cancers without membranous staining to 51.2% in cancers with strong CD138 positivity ( p < 0.0001).
3.2. TMPRSS2:ERG Fusion Status and CD138 Expression
Data on TMPRSS2:ERG fusion status obtained by FISH were available from 5,443 and by IHC from 10,994 tumors with evaluable CD138 immunostaining. Across 4,795 cases, we found a concordance of 91.6% between FISH and IHC analyzed data. Both, membranous and cytoplasmic CD138 immunopositivity, were more than 2 times more frequent in ERG positive than in ERG negative cancers ( p < 0.0001; Figure 4 ). Given this considerable difference associations between the CD138 expression, tumor phenotype and PSA recurrence were separately analyzed in ERG positive and negative cancers. All these analyses revealed similar results to the entire patient cohort for both ERG positive and ERG negative cancers (Figures 2 and 3 and Supplementary Table 1 and 2 ).
3.3. CD138 Expression, Key Genomic Deletions, and Tumor Cell Proliferation
The relationship between CD138 expression and 11 of the most frequent genomic deletions ( PTEN , 3p13, 5q21, 6q15, 13q14, 18q21, 8p21, 12p13, 12q24, 16q24, 17p13) was not only analyzed for the entire tumor cohort but also for the subgroups with identical ERG status (Figures 5 and 6 ). The analysis revealed for membranous CD138 staining significant associations with 10 deletions in all cancers, 4 deletions in ERG positive cancers, and 4 deletions in ERG negative cancers. For the cytoplasmic CD138 expression, significant associations were seen with 6 deletions in all cancers, 4 deletions in ERG positive cancers, and 6 deletions in ERG negative cancers. Most statistically significant associations were not striking. It was conspicuous, however, that 8p deletions were strongly linked to membranous and cytoplasmic CD138 positivity in both ERG positive and negative cancers ( p < 0.0001 in 3 of 4 analyses). Further subset analyses revealed that this association was strongest in low grade cancers (Gleason ≤3+4, p < 0.0001) but also retained in high grade cancers (Gleason ≤4+3, p = 0.0252). The cytoplasmic and membranous CD138 expression levels were only marginally related to tumor cell proliferation, determined by Ki67LI. Ki67LI was 2.72 ± 0.04 in 5,050 tumors with negative, 2.87 ± 0.11 in 588 tumors with weak, was 2.93 ± 0.28 in 89 tumors with moderate, and was 8.17 ± 1.06 in 6 tumors with strong cytoplasmic CD138 staining ( p < 0.0001; p = 0.0012 after Bonferroni correction). Ki67LI was 2.7 ± 0.04 in 4,688 tumors with negative, 2.86 ± 0.12 in 437 tumors with weak, was 3.1 ± 0.12 in 484 tumors with moderate, and was 2.39 ± 0.23 in 124 tumors with strong membranous CD138 staining ( p = 0.0039; data not shown).
3.4. Multivariate Analysis
To assess whether the prognostic effect of CD138 immunostaining in prostate cancer depended on already established parameters, four different multivariate analyses were performed as previously described [ 46 , 47 ]: scenario 1 analyzed the postoperative parameters (pT, pN, surgical margin status, preoperative PSA value, Gleason grade, and CD138); in scenario 2, pN was excluded, because the indication and extent of lymph node surgery is not standardized for prostate cancer; scenario 3 included mainly preoperative parameters (clinical tumor stage (cT), preoperative PSA level, prostatectomy Gleason grade, and CD138); and in scenario 4, the Gleason grade on the prostatectomy specimen was replaced by the preoperative biopsy Gleason grade which may be more impacted by sampling errors and subsequent undergrading in more than one third of cases [ 48 ]. In all scenarios, the cytoplasmic CD138 expression provided independent prognostic information ( p < 0.0001 each; Table 4 ). This association held true in the subset of ERG positive cancers ( p ≤ 0.02; Table 4 ). A separate analysis of cancers with identical traditional and quantitative Gleason grade showed a prognostic effect of the CD138 expression in Gleason 3+4 and 4+3 carcinomas (Supplementary Figure 1 ).
4. Discussion
The results of this study show that cytoplasmic CD138 immunostaining is independently linked to unfavorable tumor features and poor patient outcome in prostate cancer.
Under the experimental conditions selected for this study, benign prostate glands completely lacked CD138 staining in epithelial luminal cells while there was a strong expression in gland surrounding basal cells. A comparable pattern has previously been described by Kiviniemi et al. who found a strong CD138 staining in basal cells and only a weak staining of the basolateral cell membrane of apical cells [ 19 ]. Also, Zellweger et al. reported the CD138 expression to only occur in the basal cell layer in benign prostate glands [ 11 ]. Pathologists often use IHC to verify cancer diagnosis in prostate tissue by ensuring the absence of basal cells in prostate cancer glands by basal-cell-specific antibodies HMWCK or p63. A possible utility of CD138 immunostaining as a prostate basal cell marker applicable for cancer detection was thus earlier suggested [ 18 ].
That CD138 immunostaining was seen in glandular cells of a fraction of prostate cancers argues for overexpression of CD138 to occur during prostate cancer development. In the present study, a membranous CD138 immunostaining was seen in 19.6%, and a cytoplasmic positivity was observed in 11.2% of prostate cancers. These percentages are lower than those from earlier studies, only some of which also reported both cytoplasmic and membranous staining patterns. A membranous CD138 immunostaining was earlier described in 26% of 196 localized cancers [ 15 ], 83% of 5 metastatic cancers [ 15 ], 35% of 42 hormone-refractory cancers [ 15 ], 19% of 103 [ 25 ], and 36% of 60 cancers [ 20 ]. A cytoplasmic CD138 positivity was earlier recorded in 59% of 103 cancers [ 25 ], 64% of 60 cancers [ 20 ], 50% of 5 metastatic cancers [ 15 ], 32% of 42 hormone-refractory cancers [ 15 ], and 47% of 196 localized cancers [ 15 ]. Studies not distinguishing between membranous and cytoplasmic staining described CD138 positivity in 37% of 501 [ 11 ], 37% of 232 [ 22 ], 96% of 54 cancers [ 49 ], 38% of 32 Gleason sum 6 cancers [ 16 ], 32% of 44 Gleason sum 7 cancers [ 16 ], 38% of 99 hormone-refractory cancers [ 26 ], 3% of 151 localized cancers [ 26 ], and 42% of 12 cancers [ 19 ].
The striking association of the CD138 overexpression with patient outcome is the most relevant finding of this study. Associations of the high CD138 expression with unfavorable tumor phenotype, such as early recurrence, high Gleason grade, and poor patient outcome, had already been suggested by other studies investigating 18-551 prostate cancers by IHC [ 11 , 15 , 16 , 19 – 22 , 24 – 26 ]. Moreover, a high serum level of shed soluble CD138 protein was found to be linked to poor prognosis in another cohort of 150 prostate cancer patients [ 25 ]. The large number of cases involved in our study enabled us to differentiate the prognostic impact of membranous and cytoplasmic staining. The predominant prognostic effect of cytoplasmic staining fits with one earlier report by Contreras et al. [ 17 ] and Ledezma et al. [ 20 ] also describing a prognostic effect of cytoplasmic staining. That cytoplasmic CD138 represents an ominous feature in neoplasia is further supported by a recent own study on 1,535 breast cancers where cytoplasmic CD138 was linked to poor prognosis while membranous CD138 staining predicted a favorable disease outcome [ 50 ]. In the same study, a favorable prognostic impact of stromal CD138 staining was seen in breast cancer [ 50 ]. Stromal cell CD138 immunostaining was earlier reported to occur in prostate cancer [ 23 , 24 ], but this was not observed in our prostate cancer analysis.
CD138 is a membrane protein with largely unknown cytoplasmic functions. A possible explanation for the cytoplasmic CD138 protein accumulation, it must be considered that “membranous CD138 negativity” by IHC does not equal complete lack of CD138 protein in cell membranes. Immunohistochemical CD138 negativity of membranes only means that the CD138 protein expression level is below the detection threshold of our experimental procedure. The cytoplasmic accumulation of CD138 could potentially be explained by a protein defect or a functional mechanism preventing incorporation of CD138 into the membrane. It has also been suggested that increased CD138 shedding from cell membrane may induce the high CD138 expression and cytoplasmic CD138 accumulation in the cell, an aberrant condition that can develop during cellular dedifferentiation [ 50 ]. It appears possible that the extracellular enzyme heparanase (HPSE) plays a role in CD138 shedding by inducing proteolytic cleavage with increasing metastatic potential as result. Heparanase, which also contributes to de novo synthesis of CD138, has been shown to be overexpressed in several tumors, also in prostate cancer (summarized in [ 20 ]). The significant association between membranous and cytoplasmic CD138 expression found in our cancers would equally support the concepts of inefficient membrane integration or shedding of CD138.
The highly annotated TMA permitted us to investigate the correlation of CD138 alterations with other parameters of interest. In the present study, we selected TMPRSS2:ERG fusion as it represents the most common genomic alteration in prostate cancer, 11 chromosomal deletions because deletions are the next most prevalent genomic alterations in prostate cancer and tumor cell proliferation. TMPRSS2:ERG fusions occur in almost half of all prostate cancers and induce overexpression of the transcription factor ERG. ERG expression lacks prognostic relevance but modifies the expression of more than 1,600 genes in affected prostate epithelial cells [ 51 ]. Therefore, many proteins are upregulated or downregulated in ERG positive cancer cells in comparison to ERG negative cancer cells or normal tissues [ 51 ]. In our study, both expression and the cytoplasmic shift of CD138 are associated with the ERG expression. Shedding of CD138 from the surface is regulated at multiple levels. For examples, by agents that mediate cellular response to stress accelerated shedding or physiological agents that are involved in activation of distinct intracellular signaling pathways [ 52 ]. CD138-induced cancer-related pathways are, for example, ERK MAP and JNK MAP Kinase pathways as well as TGF- ß signaling [ 53 ]. That ERG expression is induced by ERK MAP Kinase pathway [ 54 , 55 ] might, thus, explain the predominance of the CD138 expression in ERG positive cancers.
As most chromosomal deletions are either linked to ERG positive or negative cancer [ 36 – 45 ], it was expected that several deletions are statistically linked to the CD138 expression which is also ERG related. That subgroup analyses of ERG positive and negative cancers highlighted associations of the CD138 expression and 8p deletions but otherwise showed few strong associations argues against a role of the aberrant CD138 expression for development of a genomic instability that results in double strand breaks. That the link between 8p deletion and CD138 overexpression was also retained in Gleason ≥4+3 cancers argues against a mere coincidence of these alterations in advanced tumors but raises the possibility of a functional interaction of the aberrant CD138 expression and one or several genes on 8p. However, little is currently known about which genes on 8p are most critical for prostate cancer. That no strong link was seen between CD138 expression and tumor cell proliferation argues against a relevant role of CD138 dependent processes for cell cycle control. Zellweger et al., however, earlier reported a correlation between high CD138 expression and high (>10%) Ki67LI, in a cohort of 501 prostate cancers [ 11 ].
The strong independent prognostic role of cytoplasmic CD138 immunostaining found in this study raises the possibility that CD138 measurement could provide clinically relevant prognostic information for patients. As prostate cancer is the only cancer where “active surveillance” represents an option, prognosis assessment is critical in this disease. The Gleason score is regarded the most powerful prognostic parameter which is preoperatively available, but it suffers from an interobserver variability reaching up to 40%, even between expert pathologists [ 56 ]. Future prognostic biomarkers for prostate cancer should not only be independent of currently established factors but better reproducible and thus more reliable. Given the pivotal role of the intracellular distribution of CD138, the protein represents a prognostic biomarker that probably can only be assessed by IHC. IHC is, however, notorious for reproducibility issues [ 57 ]. The advent of multiplex IHC enabling the simultaneous application of multiple antibodies also including internal controls and a computerized quantification of individual proteins may assist in making this possible.
5. Conclusions
The successful immunohistochemical analysis of 12,851 prostate cancers demonstrated a strong and largely independent association of cytoplasmic CD138 immunostaining with poor patient prognosis in prostate cancer. We consider it likely that a clinically applicable prognostic assay will consist of multiple different parameters to be measured simultaneously. The CD138 protein holds potential for becoming a component of such as a future prognostic tool.
Acknowledgments
We thank Melanie Witt, Inge Brandt, Maren Eisenberg, and Sünje Seekamp for excellent technical assistance and Dr. Wilfried Fehrle for language editing.
Data Availability
Data are available from the corresponding author on reasonable request.
Conflicts of Interest
The authors have no conflict of interest to declare.
Supplementary Materials
Supplementary Figure 1: cytoplasmic CD138 expression and PSA recurrence free survival in subgroups of classical and quantitative Gleason grade. Supplementary Table 1: cytoplasmic CD138 immunostaining and cancer phenotype in ERG subgroups. Supplementary Table 2: membranous CD138 immunostaining and cancer phenotype in ERG subgroups.
Click here for additional data file.
1 Bray F. Ferlay J. Soerjomataram I. Siegel R. L. Torre L. A. Jemal A. Global cancer statistics 2018: GLOBOCAN estimates of incidence and mortality worldwide for 36 cancers in 185 countries CA: a Cancer Journal for Clinicians 2018 68 6 394 424 10.3322/caac.21492 2-s2.0-85053395052 30207593
2 Bill-Axelson A. Holmberg L. Ruutu M. Radical prostatectomy versus watchful waiting in early prostate cancer The New England Journal of Medicine 2011 364 18 1708 1717 10.1056/NEJMoa1011967 2-s2.0-79955705831 21542742
3 Wilt T. J. Jones K. M. Barry M. J. Follow-up of prostatectomy versus observation for early prostate cancer The New England Journal of Medicine 2017 377 2 132 142 10.1056/NEJMoa1615869 2-s2.0-85024109327 28700844
4 Klotz L. Vesprini D. Sethukavalan P. Long-term follow-up of a large active surveillance cohort of patients with prostate cancer Journal of Clinical Oncology 2015 33 3 272 277 10.1200/JCO.2014.55.1192 2-s2.0-84921755394 25512465
5 Fenton J. J. Weyrich M. S. Durbin S. Liu Y. Bang H. Melnikow J. U.S. Preventive Services Task Force Evidence Syntheses, formerly systematic evidence reviews, in Prostate-Specific Antigen-Based Screening for Prostate Cancer A Systematic Evidence Review for the U.S. Preventive Services Task Force 2018 Rockville (MD) Agency for Healthcare Research and Quality (US) 30085502
6 Palaiologou M. Delladetsima I. Tiniakos D. CD138 (syndecan-1) expression in health and disease Histology and Histopathology 2014 29 2 177 189 10.14670/HH-29.177 24150912
7 Kambham N. Kong C. Longacre T. A. Natkunam Y. Utility of syndecan-1 (CD138) expression in the diagnosis of undifferentiated malignant neoplasms: a tissue microarray study of 1,754 cases Applied Immunohistochemistry & Molecular Morphology 2005 13 4 304 310 10.1097/01.pai.0000159773.50905.7b 2-s2.0-28144449815 16280658
8 Juuti A. Nordling S. Lundin J. Louhimo J. Haglund C. Syndecan-1 expression--a novel prognostic marker in pancreatic cancer Oncology 2005 68 2-3 97 106 10.1159/000085702 2-s2.0-23844491522 15886501
9 Kusumoto T. Kodama J. Seki N. Nakamura K. Hongo A. Hiramatsu Y. Clinical significance of syndecan-1 and versican expression in human epithelial ovarian cancer Oncology Reports 2010 23 4 917 925 10.3892/or_00000715 20204274
10 Hasengaowa Kodama J. Kusumoto T. Shinyo Y. Seki N. Hiramatsu Y. Prognostic significance of syndecan-1 expression in human endometrial cancer Ann Oncol 2005 16 7 1109 1115 10.1093/annonc/mdi224 2-s2.0-25444495294 15851381
11 Zellweger T. Ninck C. Mirlacher M. Tissue microarray analysis reveals prognostic significance of syndecan-1 expression in prostate cancer Prostate 2003 55 1 20 29 10.1002/pros.10209 2-s2.0-0037384548 12640657
12 Schönfeld K. Zuber C. Pinkas J. Häder T. Bernöster K. Uherek C. Indatuximab ravtansine (BT062) combination treatment in multiple myeloma: pre-clinical studies Journal of Hematology & Oncology 2017 10 1 p. 13 10.1186/s13045-016-0380-0 2-s2.0-85009958027 28077160 PMC5225632
13 Schönfeld K. Herbener P. Zuber C. Activity of indatuximab ravtansine against triple-negative breast cancer in preclinical tumor models Pharmaceutical Research 2018 35 6 p. 118 10.1007/s11095-018-2400-y 2-s2.0-85045685396 29666962 PMC5904230
14 Nageshwari B. Merugu R. Effect of levamisole on expression of CD138 and interleukin-6 in human multiple myeloma cell lines Indian Journal of Cancer 2017 54 3 566 571 10.4103/ijc.IJC_349_17 2-s2.0-85047779631 29798960
15 Brimo F. Vollmer R. T. Friszt M. Corcos J. Bismar T. A. Syndecan-1 expression in prostate cancer and its value as biomarker for disease progression BJU International 2010 106 3 418 423 10.1111/j.1464-410X.2009.09099.x 2-s2.0-77955737582 20002675
16 Chen D. Adenekan B. Chen L. Syndecan-1 expression in locally invasive and metastatic prostate cancer Urology 2004 63 2 402 407 10.1016/j.urology.2003.08.036 2-s2.0-1242296367 14972511
17 Contreras H. R. Ledezma R. A. Vergara J. The expression of syndecan-1 and -2 is associated with Gleason score and epithelial-mesenchymal transition markers, E-cadherin and beta-catenin, in prostate cancer Urologic Oncology 2010 28 5 534 540 10.1016/j.urolonc.2009.03.018 2-s2.0-77956293543 19450993
18 Edwards I. J. Proteoglycans in prostate cancer Nature Reviews. Urology 2012 9 4 196 206 10.1038/nrurol.2012.19 2-s2.0-84859631941 22349653
19 Kiviniemi J. Kallajoki M. Kujala I. Altered expression of syndecan-1 in prostate cancer APMIS 2004 112 2 89 97 10.1111/j.1600-0463.2004.apm1120202.x 2-s2.0-1642523686 15056224
20 Ledezma R. Cifuentes F. Gallegos I. Altered expression patterns of syndecan-1 and -2 predict biochemical recurrence in prostate cancer Asian Journal of Andrology 2011 13 3 476 480 10.1038/aja.2010.143 2-s2.0-79955668954 21317913 PMC3739330
21 POBLETE C. R. I. S. T. I. A. N. E. FULLA J. U. A. N. GALLARDO M. A. R. C. E. L. A. Increased SNAIL expression and low syndecan levels are associated with high Gleason grade in prostate cancer International Journal of Oncology 2014 44 3 647 654 10.3892/ijo.2014.2254 2-s2.0-84896702433 24424718 PMC3928469
22 Shariat S. F. Svatek R. S. Kabbani W. Prognostic value of syndecan-1 expression in patients treated with radical prostatectomy BJU International 2008 101 2 232 237 10.1111/j.1464-410X.2007.07181.x 2-s2.0-37349122445 17868422
23 Sharpe B. Alghezi D. A. Cattermole C. A subset of high Gleason grade prostate carcinomas contain a large burden of prostate cancer syndecan-1 positive stromal cells Prostate 2017 77 13 1312 1324 10.1002/pros.23391 2-s2.0-85028529354 28744948
24 Suhovskih A. V. Mostovich L. A. Kunin I. S. Proteoglycan expression in normal human prostate tissue and prostate cancer ISRN oncology 2013 2013 9 10.1155/2013/680136 23691363 PMC3654277
25 Szarvas T. Reis H. vom Dorp F. Soluble syndecan-1 (SDC1) serum level as an independent pre-operative predictor of cancer-specific survival in prostate cancer Prostate 2016 76 11 977 985 10.1002/pros.23186 2-s2.0-84975128720 27062540
26 Zellweger T. Ninck C. Bloch M. Expression patterns of potential therapeutic targets in prostate cancer International Journal of Cancer 2005 113 4 619 628 10.1002/ijc.20615 2-s2.0-11144322016 15472903
27 Shimada K. Anai S. Fujii T. Tanaka N. Fujimoto K. Konishi N. Syndecan-1 (CD138) contributes to prostate cancer progression by stabilizing tumour-initiating cells The Journal of Pathology 2013 231 4 495 504 10.1002/path.4271 2-s2.0-84887542459 24549646
28 Fujii T. Shimada K. Tatsumi Y. Tanaka N. Fujimoto K. Konishi N. Syndecan-1 up-regulates microRNA-331-3p and mediates epithelial-to-mesenchymal transition in prostate cancer Molecular Carcinogenesis 2016 55 9 1378 1386 10.1002/mc.22381 2-s2.0-84984985036 26259043
29 Xiao Q. Sun Y. Dobi A. Systematic analysis reveals molecular characteristics of ERG-negative prostate cancer Scientific Reports 2018 8 1 p. 12868 10.1038/s41598-018-30325-9 2-s2.0-85052301496 30150711 PMC6110738
30 Schlomm T. Iwers L. Kirstein P. Clinical significance of p53 alterations in surgically treated prostate cancers Modern Pathology 2008 21 11 1371 1378 10.1038/modpathol.2008.104 2-s2.0-57749108319 18552821
31 Sauter G. Steurer S. Clauditz T. S. Clinical utility of quantitative Gleason grading in prostate biopsies and prostatectomy specimens European Urology 2016 69 4 592 598 10.1016/j.eururo.2015.10.029 2-s2.0-84959263667 26542947
32 Kononen J. Bubendorf L. Kallionimeni A. Tissue microarrays for high-throughput molecular profiling of tumor specimens Nature Medicine 1998 4 7 844 847 10.1038/nm0798-844 2-s2.0-0031822837 9662379
33 Tennstedt P. Köster P. Brüchmann A. The impact of the number of cores on tissue microarray studies investigating prostate cancer biomarkers International Journal of Oncology 2012 40 1 261 268 10.3892/ijo.2011.1216 2-s2.0-84455163031 21956230
34 Weischenfeldt J. Simon R. Feuerbach L. Integrative genomic analyses reveal an androgen-driven somatic alteration landscape in early-onset prostate cancer Cancer Cell 2013 23 2 159 170 10.1016/j.ccr.2013.01.002 2-s2.0-84873607610 23410972
35 Minner S. Wittmer C. Graefen M. High level PSMA expression is associated with early PSA recurrence in surgically treated prostate cancer Prostate 2011 71 3 281 288 10.1002/pros.21241 2-s2.0-78951476072 20809553
36 Burkhardt L. Fuchs S. Krohn A. CHD1 is a 5q21 tumor suppressor required for ERG rearrangement in prostate cancer Cancer Research 2013 73 9 2795 2805 10.1158/0008-5472.CAN-12-1342 2-s2.0-84877747485 23492366
37 Kluth M. Hesse J. Heinl A. Genomic deletion of MAP3K7 at 6q12-22 is associated with early PSA recurrence in prostate cancer and absence of TMPRSS2:ERG fusions Modern Pathology 2013 26 7 975 983 10.1038/modpathol.2012.236 2-s2.0-84879947917 23370768
38 Krohn A. Diedler T. Burkhardt L. Genomic deletion of PTEN is associated with tumor progression and early PSA recurrence in ERG fusion-positive and fusion-negative prostate cancer The American Journal of Pathology 2012 181 2 401 412 10.1016/j.ajpath.2012.04.026 2-s2.0-84864141538 22705054
39 Krohn A. Seidel A. Burkhardt L. Recurrent deletion of 3p13 targets multiple tumour suppressor genes and defines a distinct subgroup of aggressive ERGfusion-positive prostate cancers The Journal of Pathology 2013 231 1 130 141 10.1002/path.4223 2-s2.0-84885132388 23794398
40 Kluth M. Scherzai S. Büschek F. 13q deletion is linked to an adverse phenotype and poor prognosis in prostate cancer Genes, Chromosomes & Cancer 2018 57 10 504 512 10.1002/gcc.22645 2-s2.0-85052532341 29923647
41 Kluth M. Graunke M. Möller-Koop C. Deletion of 18q is a strong and independent prognostic feature in prostate cancer Oncotarget 2016 7 52 86339 86349 10.18632/oncotarget.13404 27861151 PMC5349918
42 Kluth M. Amschler N. N. Galal R. Deletion of 8p is an independent prognostic parameter in prostate cancer Oncotarget 2017 8 1 379 392 10.18632/oncotarget.13425 2-s2.0-85009508801 27880722 PMC5352127
43 Kluth M. Ahrary R. Hube-Magg C. Genomic deletion of chromosome 12p is an independent prognostic marker in prostate cancer Oncotarget 2015 6 29 27966 27979 10.18632/oncotarget.4626 2-s2.0-84944454731 26293672 PMC4695038
44 Kluth M. Jung S. Habib O. Deletion lengthening at chromosomes 6q and 16q targets multiple tumor suppressor genes and is associated with an increasingly poor prognosis in prostate cancer Oncotarget 2017 8 65 108923 108935 10.18632/oncotarget.22408 2-s2.0-85037695489 29312579 PMC5752492
45 Kluth M. Harasimowicz S. Burkhardt L. Clinical significance of different types of p53 gene alteration in surgically treated prostate cancer International Journal of Cancer 2014 135 6 1369 1380 10.1002/ijc.28784 2-s2.0-84904056083 24523142
46 Heinrich M. C. Göbel C. Kluth M. PSCA expression is associated with favorable tumor features and reduced PSA recurrence in operated prostate cancer BMC Cancer 2018 18 1 p. 612 10.1186/s12885-018-4547-7 2-s2.0-85047931220 29855276 PMC5984312
47 Tsourlakis M. C. Eleftheriadou A. Stender A. FOXA1 expression is a strong independent predictor of early PSA recurrence in ERG negative prostate cancers treated by radical prostatectomy Carcinogenesis 2017 38 12 1180 1187 10.1093/carcin/bgx105 2-s2.0-85038641307 29029032
48 Epstein J. I. Feng Z. Trock B. J. Pierorazio P. M. Upgrading and downgrading of prostate cancer from biopsy to radical prostatectomy: incidence and predictive factors using the modified Gleason grading system and factoring in tertiary grades European Urology 2012 61 5 1019 1024 10.1016/j.eururo.2012.01.050 2-s2.0-84859426392 22336380 PMC4659370
49 Mennerich D. Vogel A. Klaman I. Shift of syndecan-1 expression from epithelial to stromal cells during progression of solid tumours European Journal of Cancer 2004 40 9 1373 1382 10.1016/j.ejca.2004.01.038 2-s2.0-2942575983 15177497
50 Kind S. Jaretzke A. Büscheck F. A shift from membranous and stromal syndecan-1 (CD138) expression to cytoplasmic CD138 expression is associated with poor prognosis in breast cancer Molecular Carcinogenesis 2019 58 12 2306 2315 10.1002/mc.23119 2-s2.0-85073817950 31545001
51 Brase J. C. Johannes M. Mannsperger H. TMPRSS2-ERG -specific transcriptional modulation is associated with prostate cancer biomarkers and TGF- β signaling BMC Cancer 2011 11 1 p. 507 10.1186/1471-2407-11-507 2-s2.0-82655183787 PMC3259213 22142399
52 Fitzgerald M. L. Wang Z. Park P. W. Murphy G. Bernfield M. Shedding of syndecan-1 and -4 ectodomains is regulated by multiple signaling pathways and mediated by a TIMP-3-sensitive metalloproteinase The Journal of Cell Biology 2000 148 4 811 824 10.1083/jcb.148.4.811 2-s2.0-0034695918 10684261 PMC2169376
53 Hayashida K. Stahl P. D. Park P. W. Syndecan-1 ectodomain shedding is regulated by the small GTPase Rab5 The Journal of Biological Chemistry 2008 283 51 35435 35444 10.1074/jbc.M804172200 2-s2.0-58149091543 18957427 PMC2602919
54 Fish J. E. Cantu Gutierrez M. Dang L. T. Dynamic regulation of VEGF-inducible genes by an ERK/ERG/p300 transcriptional network Development 2017 144 13 2428 2444 10.1242/dev.146050 2-s2.0-85021736441 28536097 PMC5536864
55 Selvaraj N. Kedage V. Hollenhorst P. C. Comparison of MAPK specificity across the ETS transcription factor family identifies a high-affinity ERK interaction required for ERG function in prostate cells Cell Communication and Signaling: CCS 2015 13 1 p. 12 10.1186/s12964-015-0089-7 2-s2.0-84928753728 PMC4338625 25885538
56 Egevad L. Ahmad A. S. Algaba F. Standardization of Gleason grading among 337 European pathologists Histopathology 2013 62 2 247 256 10.1111/his.12008 2-s2.0-84871133517 23240715
57 Goodman S. L. The antibody horror show: an introductory guide for the perplexed New Biotechnology 2018 45 9 13 10.1016/j.nbt.2018.01.006 2-s2.0-85041595613 29355666