Prostate cancer is the second most common cancer in men worldwide. IHC is used for diagnosis from prostate biopsy, though the precision and accuracy of the current biomarkers used in this test remain controversial. Therefore, many are looking for alternative, specific, and sensitive prostate cancer biomarkers to improve outcomes. Delays in screening and limitations of current biomarkers can result in prostate cancer being diagnosed at an advanced disease stage, making treatment more challenging and reducing survival rates.

While a panel of IHC prostate cancer biomarkers is commonly used for prostate cancer diagnosis (including PSA, AMACR, and high molecular weight cytokeratins), issues around benign tumors mimicking this profile and the early detection of presence and progression of prostate cancer and recurrence following clinical intervention are still not accurately validated by current biomarkers for prostate cancer. Further testing and careful interpretation of test results are essential when using these biomarker panels to ensure accurate diagnosis and appropriate management.

There remains a lack of reliable biomarkers to predict low-risk cancer and avoid overtreatment accurately. As such, aggressive forms of prostate cancer may be missed, and indolent disease may be subjected to unnecessary radical therapy. New biomarker discovery and validation promise to improve early detection and prognosis and provide therapeutic intervention targets. New tumor markers are being tested and validated to improve early detection and reduce the risk of missing aggressive or advanced disease.

Screening and Diagnosis

Screening for prostate cancer typically involves a combination of a digital rectal exam (DRE) and a prostate-specific antigen (PSA) blood test. The PSA test measures the concentration of PSA in the blood, which can be elevated in men with prostate cancer, but may also rise due to benign prostatic hyperplasia or other non-cancerous conditions. If screening results suggest the possibility of cancer, a prostate biopsy is often performed to obtain tissue samples from the prostate gland. These samples are then examined for the presence of cancer cells, providing a definitive prostate cancer diagnosis. The process of diagnosis and subsequent treatment decisions can be complex, so it is important for patients to discuss the potential benefits and risks of prostate cancer screening and diagnostic tests with their healthcare provider.

Blood Tests for Prostate Cancer

Blood tests play a crucial role in the detection and monitoring of prostate cancer. The PSA test remains the most widely used tool for prostate cancer screening, helping to identify men who may be at increased risk. However, because elevated PSA levels can also result from benign prostatic hyperplasia or inflammation, additional tests have been developed to improve diagnostic accuracy. The free PSA test measures the proportion of PSA in the blood that is not bound to proteins, which can help distinguish between prostate cancer and other prostate conditions. The prostate health index (PHI) combines total PSA, free PSA, and [-2]proPSA levels to provide a more comprehensive assessment of prostate cancer risk. These blood tests, when used together, can help guide decisions about the need for further diagnostic procedures and inform individualized patient care.

Genetic Biomarkers

Advances in research have highlighted the potential of genetic biomarkers to enhance prostate cancer diagnosis and risk assessment. Genetic biomarkers can help identify individuals with a higher risk of developing aggressive prostate cancer, enabling earlier intervention and more personalized treatment strategies. Notable examples include the TMPRSS2-ERG gene fusion, present in about half of prostate cancer cases, which is associated with tumor development and progression. Other genetic markers, such as the PCA3 gene, have been linked to an increased risk of prostate cancer and may aid in distinguishing aggressive disease from indolent forms. Ongoing research continues to explore the utility of these and other genetic biomarkers, with the goal of improving early detection, prognosis, and targeted therapy for prostate cancer patients.

Future of Prostate Cancer Diagnosis

The landscape of prostate cancer diagnosis is rapidly evolving, with new technologies poised to complement traditional screening methods like the PSA test and digital rectal examination. Emerging diagnostic tools, including genetic biomarkers and advanced imaging techniques, promise to enhance the accuracy of prostate cancer diagnosis and facilitate the early detection of aggressive disease. The analysis of circulating tumor cells (CTCs) and other novel biomarkers is also under investigation, offering the potential to provide real-time insights into tumor biology and guide personalized treatment decisions. As research progresses, these innovations are expected to improve outcomes for prostate cancer patients by enabling more precise risk stratification, reducing unnecessary repeat biopsies, and supporting the development of individualized treatment plans. The future holds promise for more effective and less invasive diagnostic strategies, ultimately leading to better prognosis and quality of life for men affected by prostate cancer.

Prostate specific antigen

PSA is the most widely known biomarker for prostate cancer. It is expressed in prostate epithelial cells and secreted to the seminal fluid, where it’s responsible for cleaving semenogelins. PSA is considered to be a highly sensitive and specific biomarker for prostate tumors. It was approved by the FDA for the diagnosis of prostate cancer in conjunction with the digital rectal exam in 1994. The PSA test measures the PSA level in blood, and results are typically reported in ng/mL (nanograms per milliliter), which helps guide further diagnostic decisions. Consequently, the detection of PSA in additional tissues via IHC is typically associated with metastatic cancer of prostatic origin, and the presence of this biomarker is often used to differentiate between prostatic and urothelial carcinomas.

Figure 1. Multiplex immunohistochemistry - Anti-Prostate Specific Antigen antibody [EP1588Y] (ab76113).

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Alpha-methylacyl-CoA racemase

AMACR is a mitochondrial and peroxisomal enzyme that functions to oxidize fatty acids and bile acid intermediates. It is over-expressed in the epithelium of approximately 80% of prostate cancer cases and acts as a robust biomarker of prostate cancer. Detection of AMACR via IHC has been shown to be important in the differential diagnosis of prostate carcinoma from benign prostate mimics. AMACR overexpression in prostate cells is indicative of poor patient prognosis, associated with a high Gleason’s score, high initial PSA levels, and indicative of an increased chance of bone metastasis.

Figure 2. Western blot - Anti-AMACR antibody [AMACR/1864] (ab268062).

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SLC45A3

SLC45A3, also known as prostein, shows a predominantly homogenous Golgi staining pattern in prostatic epithelia. It is highly specific for prostate glandular cells and thus used in the differentiation of metastatic prostate cancers from other tumor types. SLC45A3 may be expressed in PSA-negative prostate tumors, and the use of these markers in conjunction offers increased sensitivity in the identification of prostate cancer metastases. Weaker expression of SLC45A3 has been noted in some aggressive tumors, correlating with increased Gleason scores and risk of cancer relapse.

Figure 3. Immunohistochemistry (Formalin/PFA-fixed paraffin-embedded sections) - Anti-SLC45A3 antibody [EPR4795(2)] (ab137065).

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Prostate-specific membrane antigen (PSMA)

PSMA is a type II membrane glycoprotein with both folate hydrolase and N-acetylated-alpha-linked-acidic peptidase (NAALAD) activity. In contrast to PSA, PSMA is expressed in high-grade prostatic adenocarcinomas and is associated with a high Gleason score. Detection of PSMA can help to identify metastatic prostate cancer in surgical specimens, yielding higher sensitivity than PSA alone. The high sensitivity and specificity of this marker for prostatic carcinoma make it useful to differentiate prostate from urothelial tumors.

Figure 4. Immunohistochemistry (Formalin/PFA-fixed paraffin-embedded sections) - Anti-PSMA antibody [EPR6253] (ab133579).

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Prostatic acid phosphatase

PAP is an acid phosphatase enzyme expressed in prostate tissue at levels approximately two-fold greater than in other tissues. This biomarker has been investigated as a marker for metastatic prostate cancer due to its high and relatively specific expression in prostate epithelial cells and has been considered a target antigen in autologous cellular immunotherapy for patients with prostate cancer.

Knockdown of PAP expression is associated with the promotion of cell growth and tumorigenicity, leading to the development of castration-resistant androgen-specific prostate cancer.

Figure 5. Immunocytochemistry/ Immunofluorescence - Anti-PAP antibody [EPR4067] (ab109004).

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NKX3.1

NKX3.1 is a prostate-specific androgen-regulated transcription factor important in normal prostate development, regulating the proliferation of glandular epithelium and in the formation of ducts in the prostate. Due to its highly specific expression in prostate epithelial cells, NKX3.1 can be used as a diagnostic biomarker for prostate cancer and other metastatic lesions originating in the prostate. Some studies show that NKX3.1 offers improved sensitivity over PSA for the identification of poorly differentiated metastatic prostate cancer.

Figure 6. Immunohistochemistry (Formalin/PFA-fixed paraffin-embedded sections) - Anti-Nkx3.1 antibody [EPR16653] (ab196020).

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p63

A member of the p53 protein family, p63 has pleiotropic functions, including cell proliferation, survival, apoptosis, differentiation, senescence, and aging. This biomarker shows a nuclear localization in basal cells of the prostate and is absent from usual-type acinar prostate cancers. Aberrant p63 expression in prostate cancers may represent a molecularly distinct subclass and rare tumor type, with some studies suggesting that further research of this biomarker may yield identification of the prostate cancer cell-of-origin.

Figure 7. Flow Cytometry (Intracellular) - Anti-p63 antibody [EPR5701] (ab124762).

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ERG

ERG is a transcriptional regulator that is identified in approximately half of all prostatic adenocarcinomas. This emerging biomarker for prostate cancer localizes to the nucleus of cells and is commonly found as a fusion product with TMPRSS2 or SLC45A3. These ERG fusion products play an important role in the carcinogenesis of prostate cancer and may be predictive biomarkers of prostate cancer.

Figure 8. Flow Cytometry (Intracellular) - Anti-ERG antibody [EPR3864] (ab92513).

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PTEN

PTEN (phosphatase and tensin homolog) is a tumor suppressor gene frequently altered in prostate cancer. It encodes a dual-specificity phosphatase that regulates cell growth by antagonizing the PI3K/AKT signaling pathway. Loss or mutation of PTEN leads to increased AKT activity, promoting cell survival and proliferation. PTEN also modulates protein phosphorylation, influencing pathways involved in tumor progression. Its inactivation is associated with aggressive prostate cancer and resistance to therapy. Monitoring PTEN status can support research into disease mechanisms and therapeutic development, making it a valuable marker in prostate cancer studies.

Figure 9. Immunohistochemistry (Formalin/PFA-fixed paraffin-embedded sections) - Anti-PTEN antibody [EPR9941-2] (ab170941).

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Fatty acid synthase

This enzyme plays a role in the synthesis of long-chain fatty acids. Increased fatty acid synthase expression has been observed in high-grade PIN (prostatic intraepithelial neoplasia) lesions, highlighting its potential as an early marker of tumor aggressiveness. Fatty acid synthase overexpression is an emerging biomarker linked to prostate cancer carcinogenesis. Studies suggest that this emerging biomarker may act in cancer by inhibiting apoptosis and associating fatty acid synthase overexpression in prostate cancer IHC with increased Gleason score and more aggressive tumors.

Figure 10. Immunocytochemistry/ Immunofluorescence - Anti-Fatty Acid Synthase antibody [EPR7466] (ab128870).

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FOXA1

Mutations in the FOXA1 transcription factor have been associated with tumor progression in prostate cancer. IHC analysis of FOXA1 as a prostate cancer biomarker has identified overexpression in prostate cancer metastases and linked this biomarker with more aggressive, castration-resistant cancer types. It may also act as an independent predictor of recurrence.

Figure 10. Western blot - Anti-FOXA1 antibody [EPR10881] (ab170933).

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Prostate secretory protein 94

PSP94 (prostate secretory protein of 94 aa; also called PIP) is one of the major secretory proteins from the prostate gland. This potential prostate cancer biomarker shows decreasing expression as prostate cancer progresses from a hormone-dependent to a hormone-independent state, with a complete lack of PSP94 production in highly advanced metastatic prostate cancer. This differential expression could make PSP94 a prognostic clinical marker for prostate cancer and could help distinguish patients with aggressive forms of prostate cancer.

Figure 11. Immunohistochemistry (Formalin/PFA-fixed paraffin-embedded sections) - Anti-Prostate Secretory Protein/PSP antibody [EPR7346] (ab133296).

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Vascular endothelial growth factor

VEGFA is a mediator of angiogenesis and tumor proliferation in many cancer types. Initial studies in prostate cancer suggest it may act as a prognostic biomarker for aggressive forms of prostate cancer and could be used to select prostate cancer patients suitable for novel anti-angiogenic therapies. VEGFA expression has been shown to be significantly elevated in cases of prostatic cancer compared to benign hyperplasia, demonstrating it may serve as a potential diagnostic biomarker. Further, expression levels of VEGFA correlated with cancer grading, suggesting its utility as a prognostic marker. View antibodies to VEGFA.

Figure 12. Immunocytochemistry/ Immunofluorescence - Anti-VEGFA antibody [EP1176Y] - C-terminal (ab52917).

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p27-kip1

In normal tissue, p27^kip1 is a tumor suppressor that inhibits cyclin/cyclin-dependent kinase (CDK) cell cycle progression and regulates cancer cell invasion and migration. Decreased expression of p27^kip1 is associated with poor patient prognosis in prostate adenocarcinomas. Additionally, cytoplasmic localization of p27^kip1 has been linked to cyclin/CDK-independent roles in tumorigenicity.

Figure 13. Immunoprecipitation - Anti-p27 KIP 1 antibody [Y236] (ab32034).

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Cytokeratin 5

Cytokeratin 5 (CK5) is a type of intermediate filament protein found in the basal cells of epithelial tissues, including the prostate. In prostate cancer diagnostics, CK5 is commonly used to help distinguish benign from malignant tissue. Its expression is typically absent in prostate adenocarcinoma, making it a useful marker when combined with others like p63. CK5 staining supports the identification of basal cell layers, aiding pathologists in evaluating biopsy samples. While not used alone, CK5 contributes to a broader panel of markers that improve diagnostic accuracy in prostate cancer research and clinical practice.

Figure 14. Immunohistochemistry (Formalin/PFA-fixed paraffin-embedded sections) - Anti-wide spectrum Cytokeratin antibody (ab9377).

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Cytokeratin 6

CK6 is a basic cytokeratin that dimerizes with cytokeratin 16/17 for function. CK6 is a cytoskeletal protein and serves as a marker for prostate basal cells, showing similar localization to CK5 of diffuse cytoplasmic staining with enrichment in the perinuclear area. Negative staining of this marker is often used in conjunction with CK5- and AMACR+ staining to diagnose problematic prostatic cancers.

Figure 15. Immunohistochemistry (Formalin/PFA-fixed paraffin-embedded sections) - Anti-Cytokeratin 6 antibody [EPR1603Y] (ab52620).

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Kallikrein 2

Kallikrein 2 (KLK2) is a trypsin-like serine protease predominantly expressed in the prostate gland, where its production is regulated by androgen signaling. KLK2 undergoes post-translational modifications to become enzymatically active. Within prostate tissue, KLK2 plays a functional role upstream of prostate-specific antigen (PSA), contributing to the activation of this widely used prostate cancer biomarker. This enzymatic cascade is also linked to the liquefaction of seminal plasma, a physiological process important for male fertility. KLK2’s expression and activity patterns make it a relevant target in prostate cancer research, particularly in studies focused on biomarker development and disease progression.

Figure 16. Western blot - Anti-Kallikrein 2/KLK2 antibody (ab232980).

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