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Stimulator of interferon genes protein (STING) activates the immune response in inflammatory cells. STING expression in cancer cells is less well characterized, but STING agonists are currently being evaluated as anticancer drugs. A tissue microarray containing 18,001 samples from 139 different tumor types was analyzed for STING by immunohistochemistry. STING-positive tumor cells were found in 130 (93.5%) of 139 tumor entities. The highest STING positivity rates occurred in squamous cell carcinomas (up to 96%); malignant mesothelioma (88.5%–95.7%); adenocarcinoma of the pancreas (94.9%), lung (90.3%), cervix (90.0%), colorectum (75.2%), and gallbladder (68.8%); and serous high-grade ovarian cancer (86.0%). High STING expression was linked to adverse phenotypes in breast cancer, clear cell renal cell carcinoma, colorectal adenocarcinoma, hepatocellular carcinoma, and papillary carcinoma of the thyroid (p < 0.05). In pTa urothelial carcinomas, STING expression was associated with low-grade carcinoma (p = 0.0002). Across all tumors, STING expression paralleled PD-L1 positivity of tumor and inflammatory cells (p < 0.0001 each) but was unrelated to the density of CD8+ lymphocytes. STING expression is variable across tumor types and may be related to aggressive tumor phenotype and PD-L1 positivity. The lack of relationship with tumor-infiltrating CD8+ lymphocytes argues against a significant IFN production by STING positive tumor cells.

EpCAM is expressed in many epithelial tumors and is used for the distinction of malignant mesotheliomas from adenocarcinomas and as a surrogate pan-epithelial marker. A tissue microarray containing 14,832 samples from 120 different tumor categories was analyzed by immunohistochemistry. EpCAM staining was compared with TROP2 and CKpan. EpCAM staining was detectable in 99 tumor categories. Among 78 epithelial tumor types, the EpCAM positivity rate was ≥90% in 60 categories—including adenocarcinomas, neuroendocrine neoplasms, and germ cell tumors. EpCAM staining was the lowest in hepatocellular carcinomas, adrenocortical tumors, renal cell neoplasms, and in poorly differentiated carcinomas. A comparison of EpCAM and CKpan staining identified a high concordance but EpCAM was higher in testicular seminomas and neuroendocrine neoplasms and CKpan in hepatocellular carcinomas, mesotheliomas, and poorly differentiated non-neuroendocrine tumors. A comparison of EpCAM and TROP2 revealed a higher rate of TROP2 positivity in squamous cell carcinomas and lower rates in many gastrointestinal adenocarcinomas, testicular germ cell tumors, neuroendocrine neoplasms, and renal cell tumors. These data confirm EpCAM as a surrogate epithelial marker for adenocarcinomas and its diagnostic utility for the distinction of malignant mesotheliomas. In comparison to CKpan and TROP2 antibodies, EpCAM staining is particularly common in seminomas and in neuroendocrine neoplasms.

Androgen receptor (AR) is a transcription factor expressed in various normal tissues and is a therapeutic target for prostate and possibly other cancers. A TMA containing 18,234 samples from 141 different tumor types/subtypes and 608 samples of 76 different normal tissue types was analyzed by immunohistochemistry. AR positivity was found in 116 tumor types including 66 tumor types (46.8%) with ≥1 strongly positive tumor. Moderate/strong AR positivity was detected in testicular sex cord-stromal tumors (93.3–100%) and neoplasms of the prostate (79.3–98.7%), breast (25.0–75.5%), other gynecological tumors (0.9–100%), kidney (5.0–44.1%), and urinary bladder (5.4–24.2%). Low AR staining was associated with advanced tumor stage (pTa versus pT2-4; p < 0.0001) in urothelial carcinoma; advanced pT (p < 0.0001), high tumor grade (p < 0.0001), nodal metastasis (p < 0.0001), and reduced survival (p = 0.0024) in invasive breast carcinoma; high pT (p < 0.0001) and grade (p < 0.0001) in clear cell renal cell carcinoma (RCC); and high pT (p = 0.0055) as well as high grade (p < 0.05) in papillary RCC. AR staining was unrelated to histopathological/clinical features in 157 endometrial carcinomas and in 221 ovarian carcinomas. Our data suggest a limited role of AR immunohistochemistry for tumor distinction and a prognostic role in breast and clear cell RCC and highlight tumor entities that might benefit from AR-targeted therapy.

The role of CD10 expression in colorectal cancer has been controversially discussed in the literature. Some data suggest a predictive capacity for lymph node and liver metastases, thus influencing overall survival (OS) and disease-free survival (DFS). This study aims to analyse the relationship between CD10 expression and overall survival (OS) in a European cohort. To determine the association of CD10 expression with tumour phenotype, molecular features, and prognosis, a tissue microarray of 1469 colorectal carcinomas was analysed using immunohistochemistry and was compared with matched clinicopathologic data. CD10 expression correlated with earlier tumour stages (p = 0.017) and left-sided colon cancer (p < 0.001). However, no correlation was found between CD10 expression and lymph node involvement (p = 0.711), tumour grading (p = 0.397), or overall survival (p = 0.562). Even in the subgroup analysis of tumour or nodal stage, CD10 did not affect overall survival, although it was significantly associated with p53 and nuclear β-catenin expression (p = 0.013 and p < 0.001, respectively). CD10 expression correlates with earlier tumour stages, colon cancer location, and indicators of aggressive CRC subtypes. However, we can exclude CD10 as a relevant independent prognosticator for CRC.

Prognostic markers in routine clinical management of breast cancer are often assessed using RNA-based multi-gene panels that depend on fluctuating tumor purity. Multiplex fluorescence immunohistochemistry (mfIHC) holds the potential for an improved risk assessment. To enable automated prognosis marker detection (i.e., progesterone receptor [PR], estrogen receptor [ER], androgen receptor [AR], GATA3, TROP2, HER2, PD-L1, Ki67, TOP2A), a framework for automated breast cancer identification was developed and validated involving thirteen different artificial intelligence analysis steps and an algorithm for cell distance analysis using 11+1-marker-BLEACH&STAIN-mfIHC staining in 1404 invasive breast cancers of no special type (NST). The framework for automated breast cancer detection discriminated normal glands from malignant glands with an accuracy of 98.4%. This approach identified that five (PR, ER, AR, GATA3, PD-L1) of nine biomarkers were associated with prolonged overall survival (p ≤ 0.0095 each) and two of these (PR, AR) were found to be independent risk factors in multivariate analysis (p ≤ 0.0151 each). The combined assessment of PR-ER-AR-GATA3-PD-L1 as a five-marker prognosis score showed strong prognostic relevance (p < 0.0001) and was an independent risk factor in multivariate analysis (p = 0.0034). Automated breast cancer detection in combination with an artificial intelligence-based analysis of mfIHC enables a rapid and reliable analysis of multiple prognostic parameters. The strict limitation of the analysis to malignant cells excludes the impact of fluctuating tumor purity on assay precision.

Background: This prospective study assesses the use of rapid remote online cytological evaluation for diagnosing endoscopical achieved biopsies. It focuses on its effectiveness in identifying benign and malignant conditions using digital image processing. Methods: The study was conducted between April 2021 and September 2022 and involved analyses of 314 Rapid Remote Online Cytological Evaluations in total (154 imprint cytologies, 143 fine needle aspirations and 17 brush cytologies) performed on 239 patients at the LungenClinic Grosshansdorf. During on-site evaluation via telecytology, the time requirement was recorded and the findings were compared with the cyto-/histological and final diagnoses. Results: By means of rapid remote online evaluation, findings of 86 cytological benign, 190 malignant and 38 unclear diagnoses were recorded (Ø assessment time, 100 s; range, 11–370 s). In 27 of the 37 specimens with unclear diagnoses, the final findings were malignant tumours and only 6 were benign changes. The diagnosis of another 4 of these 37 findings remained unclear. Excluding these 37 specimens, rapid remote online evaluation achieved a sensitivity of 90.5% with a specificity of 98.5% and a correct classification rate of 92.4% with regard to the final diagnosis of all cases. As expected, an increase in the sensitivity rate for the cytological detection of malignant tumours (76.1% vs. 92.5%) was found especially in fine-needle aspirations. Conclusions: Rapid remote online analysis allows the fast quantitative and qualitative evaluation of clinically obtained cytological specimens. With a correct classification rate of more than 93%, sampling deficiencies can be corrected promptly and diagnostic and therapeutic approaches can be derived.

Prostate-specific acid phosphatase (PSAP) is a marker for prostate cancer. To assess the specificity and prognostic impact of PSAP, 14,137 samples from 127 different tumor (sub)types, 17,747 prostate cancers, and 76 different normal tissue types were analyzed via immunohistochemistry in a tissue microarray format. In normal tissues, PSAP staining was limited to the prostate epithelial cells. In prostate cancers, PSAP was seen in 100% of Gleason 3 + 3, 95.5% of Gleason 4 + 4, 93.8% of recurrent cancer under androgen deprivation therapy, 91.0% of Gleason 5 + 5, and 31.2% of small cell neuroendocrine cancer. In non-prostatic tumors, PSAP immunostaining was only found in 3.2% of pancreatic neuroendocrine tumors and in 0.8% of diffuse-type gastric adenocarcinomas. In prostate cancer, reduced PSAP staining was strongly linked to an advanced pT stage, a high classical and quantitative Gleason score, lymph node metastasis, high pre-operative PSA levels, early PSA recurrence (p < 0.0001 each), high androgen receptor expression, and TMPRSS2:ERG fusions. A low level of PSAP expression was linked to PSA recurrence independent of pre- and postoperative prognostic markers in ERG-negative cancers. Positive PSAP immunostaining is highly specific for prostate cancer. Reduced PSAP expression is associated with aggressive prostate cancers. These findings make PSAP a candidate marker for prognostic multiparameter panels in ERG-negative prostate cancers.

Human mammaglobin-A (SCGB2A2) is a secretory protein with an unknown function that is used as a diagnostic marker for breast cancer. However, other tumors can also express mammaglobin-A. To comprehensively study patterns of mammaglobin-A expression, a tissue microarray containing 16,328 samples from 128 different tumor types as well as 608 samples of 76 different normal tissue types was analyzed using immunohistochemistry. Mammaglobin-A positivity was found in only a few normal tissues, including luminal cells of the breast as well as endocervical and endometrial glands. In tumor tissues, 37 of 128 tumor categories showed mamma-globin-A staining, 32 of which were derived from one of four organs: breast (6 tumor categories), endometrium (5 tumor categories), ovary (5 tumor categories), and salivary glands (16 tumor categories). Only five additional tumor types showed occasional weak mammaglobin positivity, including medullary thyroid cancer, teratoma of the testis, squamous cell carcinoma of the skin and pharynx, and prostatic adenocarcinoma. Among 1139 evaluable invasive breast carcinomas of no special type, low mammaglobin-A immunostaining was linked to high BRE grade (p = 0.0011), loss of estrogen and progesterone receptor expression (p < 0.0001 each), and triple-negative status (p < 0.0001) but not to patient survival. In endometrial cancer, mammaglobin-A loss was linked to an advanced tumor stage (p = 0.0198). Our data characterize mammaglobin-A as a highly specific marker for tumors derived from either the breast, female genitals, or salivary gland.

As a result of its expression in corresponding normal cell types, inhibin alpha (INHA) is used as an immunohistochemical marker for adrenocortical neoplasms and testicular or ovarian sex cord stromal tumors. However, other tumors can also express INHA. To comprehensively determine INHA expression in cancer, a tissue microarray containing 15,012 samples from 134 different tumor types and subtypes was analyzed by immunohistochemistry. INHA positivity was found in 72 of 134 tumor categories, including 26 categories with ≥1 strongly positive case. A moderate to strong INHA positivity was found in 100% of 37 granulosa cell tumors of the ovary, 100% of 43 other sex cord stromal tumors of the ovary/testis, 100% of 31 granular cell tumors, 78.5% of 28 adenomas, 44% of 25 carcinomas of the adrenal cortex, and 46.7% of 15 pancreatic acinar cell carcinomas. At least a weak INHA positivity was seen in

Uroplakin 3B (Upk3b) is involved in stabilizing and strengthening the urothelial cell layer of the bladder. Based on RNA expression studies, Upk3b is expressed in a limited number of normal and tumor tissues. The potential use of Upk3b as a diagnostic or prognostic marker in tumor diagnosis has not yet been extensively investigated. A tissue microarray containing 17,693 samples from 151 different tumor types/subtypes and 608 samples of 76 different normal tissue types was analyzed by immunohistochemistry. In normal tissues, Upk3b expression was largely limited to mesothelial cells, urothelial umbrella cells, and amnion cells. In tumor tissues, Upk3b was detectable in only 17 of 151 (11.3%) of tumor types. Upk3b expression was most frequent in mesotheliomas (82.1% of epithelioid and 30.8% of biphasic) and in urothelial tumors of the urinary bladder, where the positivity rate decreased from 61.9% in pTaG2 (low grade) to 58.0% in pTaG3 (high grade) and 14.6% in pT2-4 cancers. Among pT2-4 urothelial carcinomas, Upk3b staining was unrelated to tumor stage, lymph node status, and patient prognosis. Less commonly, Upk3b expression was also seen in Brenner tumors of the ovary (10.8%), as well as in four other subtypes of ovarian cancer (0.9–10.6%). Four additional tumor entities showed a weak to moderate Upk3b positivity in less than 5% of cases. In summary, Upk3b immunohistochemistry is a useful diagnostic tool for the distinction of mesotheliomas from other thoracic tumors and the visualization of normal mesothelial and umbrella cells.

Background: Although quantification of tumor infiltrating lymphocytes (TILs) has become of increasing interest in immuno-oncology, only little is known about TILs infiltration in the tumor microenvironment and its predictive value in vulvar cancer. Methods: Immunohistochemistry and automated digital image analysis was applied to measure the densities of CD3+ (DAKO, #IR503) and CD8+ (DAKO, #IR623) TILs at the invasive margin and in the center of 530 vulvar squamous cell cancers. Results: An elevated density of CD3+ T-cell at the invasive margin was significantly associated with low tumor stage (p = 0.0012) and prolonged survival (overall survival [OS] p = 0.0027, progression free survival [PFS] p = 0.024) and was independent from tumor stage, nodal stage, grade, and HPV-status in multivariate analysis (p < 0.05). The prognostic impact of CD3+ cells in the center of the tumor was weaker compared to the invasive margin (OS p = 0.046, PFS p = 0.031) and lacking for CD8+ T-cell densities at any location (p ≥ 0.14 each). Unsupervised clustering of CD3+ and CD8+ T-cell densities identified three major subgroups corresponding to the immune desert (137 patients), immune excluded (220 patients) and immune inflamed phenotypes (133 patients). Survival analysis revealed a particular poor prognosis for the immune desert phenotype for OS (p = 0.0071) and PFS (p = 0.0027). Conclusion: Our data demonstrate a high prognostic value of CD3+ T-cells at the invasive margin and immune phenotypes in vulvar squamous cell cancer.

The current risk stratification in prostate cancer (PCa) is frequently insufficient to adequately predict disease development and outcome. One hallmark of cancer is telomere maintenance. For telomere maintenance, PCa cells exclusively employ telomerase, making it essential for this cancer entity. However, TERT, the catalytic protein component of the reverse transcriptase telomerase, itself does not suit as a prognostic marker for prostate cancer as it is rather low expressed. We investigated if, instead of TERT, transcription factors regulating TERT may suit as prognostic markers. To identify transcription factors regulating TERT, we developed and applied a new gene regulatory modeling strategy to a comprehensive transcriptome dataset of 445 primary PCa. Six transcription factors were predicted as TERT regulators, and most prominently, the developmental morphogenic factor PITX1. PITX1 expression positively correlated with telomere staining intensity in PCa tumor samples. Functional assays and chromatin immune-precipitation showed that PITX1 activates TERT expression in PCa cells. Clinically, we observed that PITX1 is an excellent prognostic marker, as concluded from an analysis of more than 15,000 PCa samples. PITX1 expression in tumor samples associated with (i) increased Ki67 expression indicating increased tumor growth, (ii) a worse prognosis, and (iii) correlated with telomere length.

Angiotensin-converting enzyme 2 (ACE2) is a regulator in the renin-angiotensin system. ACE2 expression was analysed immunohistochemically in 15,306 samples from 119 tumour types and in 608 samples of 76 normal tissue types. In normal tissue, ACE2 was most abundant in testis and corpus luteum, kidney, small intestine and capillaries of selected organs. At least an occasional weak ACE2 positivity of tumour cells was seen in 83 of 119 (70%) tumour types. ACE2 tumour cell positivity was particularly frequent in papillary (94%) and clear cell (86%) renal cell carcinoma, colorectal adenocarcinoma (81%), mucinous ovarian cancer (61%), cholangiocarcinoma (58%), hepatocellular carcinoma (56%), and in adenocarcinomas of the stomach (47%), pancreas (42%), and the lung (35%). ACE2-positive capillaries were found in 409/12,644 (3%) of analysable tumours, most frequently in tumours with endocrine/neuroendocrine activity. Presence of ACE2-positive capillaries was linked to low stage in papillary thyroid cancer and low grade in neuroendocrine neoplasms. In conclusion, ACE2 expression can occur both in tumour cells and tumour-associated capillaries in a broad variety of different tumour types at highly variable frequencies.

Arginase-1 catalyzes the conversion of arginine to ornithine and urea. Because of its predominant expression in hepatocytes, it serves as a marker for hepatocellular carcinoma, although other tumor entities can also express arginase-1. To comprehensively determine arginase-1 expression in normal and neoplastic tissues, tissue microarrays containing 14,912 samples from 117 different tumor types and 608 samples of 76 different normal tissue types were analyzed by immunohistochemistry. In normal tissues, arginase-1 was expressed in the liver, the granular layer of the epidermis, and in granulocytes. Among tumors, a nuclear and cytoplasmic arginase-1 immunostaining was predominantly observed in hepatocellular carcinoma, where 96% of 49 cancers were at least moderately positive. Although 22 additional tumor categories showed occasional arginase immunostaining, strong staining was exceedingly rare in these entities. Staining of a few tumor cells was observed in squamous cell carcinomas of various sites. Staining typically involved maturing cells with the beginning of keratinization in these tumors and was significantly associated with a low grade in 635 squamous cell carcinomas of various sites (p = 0.003). Teratoma, urothelial carcinoma and pleomorphic adenomas sometimes also showed arginase expression in areas with squamous differentiation. In summary, arginase-1 immunohistochemistry is highly sensitive and specific for hepatocellular carcinoma if weak and focal staining is disregarded.

Mesothelin (MSLN) represents an attractive molecule for targeted cancer therapies. To identify tumors that might benefit from such therapies, tissue microarrays including 15,050 tumors from 122 different tumor types and 76 healthy organs were analyzed for MSLN expression by immunohistochemistry. Sixty-six (54%) tumor types showed at least occasional weak staining, including 50 (41%) tumor types with at least one strongly positive sample. Highest prevalence of MSLN positivity had ovarian carcinomas (serous 97%, clear cell 83%, endometrioid 77%, mucinous 71%, carcinosarcoma 65%), pancreatic adenocarcinoma (ductal 75%, ampullary 81%), endometrial carcinomas (clear cell 71%, serous 57%, carcinosarcoma 50%, endometrioid 45%), malignant mesothelioma (69%), and adenocarcinoma of the lung (55%). MSLN was rare in cancers of the breast (7% of 1138), kidney (7% of 807), thyroid gland (1% of 638), soft tissues (0.3% of 931), and prostate (0 of 481). High expression was linked to advanced pathological tumor (pT) stage (p < 0.0001) and metastasis (p < 0.0001) in 1619 colorectal adenocarcinomas, but unrelated to parameters of malignancy in 1072 breast-, 386 ovarian-, 174 lung-, 757 kidney-, 171 endometrial-, 373 gastric-, and 925 bladder carcinomas. In summary, numerous important cancer types with high-level MSLN expression might benefit from future anti-MSLN therapies, but MSLN’s prognostic relevance appears to be limited.

Colorectal cancer (CRC) is a heterogeneous disease that results from the accumulation of mutations in colonic mucosa cells. A subclass of CRC is characterized by microsatellite instability, which is thought to occur mainly through inactivation of the DNA mismatch repair genes MLH1 and MSH2. The inositol 5-phosphatase SHIP1 is expressed predominantly in hematopoietic cells. In this study, the expression of SHIP1 in carcinomas and its putative correlation with clinicopathologic parameters, expression of DNA repair genes and microsatellite instability was investigated. By analyzing a multi-tumor tissue microarray, expression of SHIP1 was detected in 48 out of 72 cancer entities analyzed. The expression of SHIP1 protein of 145 kDa was confirmed by Western blot analysis in 7 out of 14 carcinoma cell lines. Analysis of a large colorectal cancer tissue microarray with 1009 specimens revealed SHIP1 expression in 62% of the samples analyzed. SHIP1 expression was inversely correlated with lymph node metastasis, vascular invasion and tumor grade, and it was positively associated with left-sided tumor localization. Interestingly, a strong relationship between the expression of SHIP1 and nuclear and membranous beta-catenin and the DNA repair genes MLH1 and MSH2 was observed.

Background: Pathological routine lymph node staging is postulated to be the main oncological prognosticator in esophageal cancer (EC). However, micrometastases in lymph nodes (LNMM) and bone marrow (BNMM) are discussed as the key events in tumor recurrence. We assessed the prognostic significance of the LNMM/BNMM status in initially pN0 staged patients with curative esophagectomy. Methods: From 110 patients bone marrow aspirates and lymph node tissues were analyzed. For LNMM detection immunohistochemistry was performed using the anticytokeratin antibody AE1/AE3. To detect micrometastases in the bone marrow a staining with the pan-keratin antibody A45-B/B3 was done. Results were correlated with clinicopathologic parameters as well as recurrence and death during follow-up time. Results: Thirty-eight (34.5%) patients showed LNMM, whereas in 54 (49.1%) patients BNMM could be detected. LNMM and BNMM positive patients showed a correlation to an increased pT category (p = 0.017). Univariate and multivariate analyses revealed that the LNMM/BNMM status and especially LNMM skipping the anatomical lymph node chain were significant independent predictors of overall survival and recurrence-free survival. Conclusions: This study indicates that routine pathological staging of EC is insufficient. Micrometastases in lymph nodes and the bone marrow seem to be the main reason for tumor recurrence and they are a strong prognosticator following curative treatment of pN0 EC.

The formation of distant metastases often determines the fate of patients with head and neck squamous cell carcinoma (HNSCC). The expression of cell adhesion molecules (CAMs) and their ligands of the leukocyte adhesion cascade has been associated with metastatic competence in several malignant entities. In this study, human HNSCC cell lines were analyzed in vitro and in a spontaneous metastatic xenograft model. Immunohistochemical analyses of several CAMs were performed on xenograft tumors and tissue microarrays (TMA) from 453 patients with head and neck squamous cell carcinomas with full histo-pathological and clinical follow-up data. UTSCC 24A and 24B cells bind to E-selectin in vitro, show E-selectin dependent binding to human umbilical vein endothelial cells (HUVECs), and express sLeX. All HNSCC cells engrafted into severe combined immunodeficient (SCID) mice, and UTSCC 24A cells formed sporadically spontaneous lung metastases. The expression of CAMs varied between the cell lines, but a correlation between tumor growth and metastatic potential did not exist. None of the CAMS or their ligands could be identified to be of prognostic relevance in the TMA study. The in vitro results indicate that E-selectin and sLeX are involved in the adhesion of HNSCC cells to endothelium. However, specific prognostic markers chosen from the leukocyte adhesion cascade for HNSCC were not identified.

The VEGFR-1 is suggested to promote tumor progression. In the current study we analyzed prevalence and prognostic impact of the VEGFR-1 by immunohistochemistry on a tissue microarray containing more than 3000 prostate cancer specimens. Results were compared to tumor phenotype, ETS-related gene (ERG) status, and biochemical recurrence. Membranous VEGFR-1 expression was detectable in 32.6% of 2669 interpretable cancers and considered strong in 1.7%, moderate in 6.7% and weak in 24.2% of cases. Strong VEGFR-1 expression was associated with TMPRSS2:ERG fusion status as determined by fluorescence in situ hybridization (FISH) and immunohistochemistry (p < 0.0001 each). Elevated VEGFR-1 expression was linked to high Gleason grade and advanced pT stage in TMPRSS2:ERG negative cancers (p = 0.0008 and p = 0.001), while these associations were absent in TMPRSS2:ERG positive cancers. VEGFR-1 expression was also linked to phosphatase and tensin homolog (PTEN) deletions. A comparison with prostate specific antigen (PSA) recurrence revealed that the 1.7% of prostate cancers with the highest VEGFR-1 levels had a strikingly unfavorable prognosis. This could be seen in all cancers, in the subsets of TMPRSS2:ERG positive or negative, PTEN deleted or undeleted carcinomas (p < 0.0001 each). High level VEGFR-1 expression is infrequent in prostate cancer, but identifies a subgroup of aggressive cancers, which may be candidates for anti-VEGFR-1 targeted therapy.