Prostate cancer (PCa) is one of the most common cancers in men worldwide, with approximately 1.4 million new cases and 375,000 deaths annually. While genetic research has advanced our understanding significantly, genetics alone cannot explain the full complexity of how prostate cancer grows, spreads, and resists treatment.
The tumor microenvironment (TME) is the ecosystem surrounding cancer cells -- made up of immune cells, blood vessels, structural support cells, and even microorganisms. These components interact constantly with cancer cells, influencing how aggressively a tumor grows and how well treatments work.
A major challenge in advanced prostate cancer is the progression to castration-resistant prostate cancer (CRPC) -- a stage where tumors no longer respond to standard hormone-blocking therapy called androgen deprivation therapy (ADT). The microenvironment plays a central role in driving this resistance.
This review synthesizes recent research on four key microenvironmental components: immune cells, the vascular system, stromal cells, and microbiota, with the goal of identifying new targets for diagnosis and treatment.
The prostate tumor microenvironment contains diverse immune cells including T lymphocytes, B cells, tumor-associated macrophages (TAMs), and myeloid-derived suppressor cells (MDSCs). Rather than mounting an effective attack on cancer, many of these cells are redirected by the tumor into roles that support its growth.
Androgen receptor (AR) signaling -- the same pathway that drives prostate cancer cell growth -- also directly suppresses immune defenses. AR upregulates the immune checkpoint protein PD-L1, which weakens T cells and natural killer (NK) cells, helping the tumor evade immune surveillance.
MDSCs are immature immune cells that are abnormally abundant in prostate tumors. They reduce the infiltration of cancer-killing CD8+ T cells and secrete interleukin-23 (IL-23), a molecule that promotes CRPC progression and resistance to androgen deprivation therapy. Blocking IL-23 or MDSC recruitment is a promising therapeutic direction.
Different subsets of T cells play opposing roles. Th1 cells support anti-tumor immunity and are associated with better prognosis, while Th2 cells and regulatory T cells (Tregs) promote tumor progression and help cancer cells evade detection. Cytotoxic T lymphocytes (CTLs) can kill prostate cancer cells but are often suppressed by inhibitory signals within the TME.
Angiogenesis -- the formation of new blood vessels -- is a critical process that prostate tumors exploit to secure nutrients and oxygen. New vessels also serve as highways that allow cancer cells to spread to distant organs, making angiogenesis directly linked to metastasis and poor prognosis.
The VEGF (vascular endothelial growth factor) family is the most potent driver of tumor angiogenesis in prostate cancer. VEGF-A activates signaling pathways including Ras/MAPK and PI3K/Akt, stimulating endothelial cells to proliferate, migrate, and form new blood vessels. VEGF also modulates immune cells within the tumor, further reinforcing immune escape.
The FGF (fibroblast growth factor) family plays a complementary role, stimulating cell division, migration, and differentiation. FGF1 and FGF2 are the most studied members; FGF2 directly stimulates angiogenesis and may contribute to the transition of prostate cancer to the treatment-resistant CRPC state.
The PDGF (platelet-derived growth factor) family contributes to invasion and metastasis by promoting tumor cell spread into surrounding tissues. PDGF also indirectly boosts angiogenesis by upregulating VEGF expression, creating a reinforcing cycle of blood vessel growth that continuously supplies the growing tumor.
Stromal cells normally maintain the physical structure of prostate tissue, but during cancer development they are reprogrammed to support tumor invasion. They remodel the extracellular matrix (ECM) -- the scaffold between cells -- making the tissue environment more permissive for cancer cell infiltration and spread.
Cancer-associated fibroblasts (CAFs) are the most influential stromal cells in the prostate tumor microenvironment. Activated by signals from cancer cells including interleukin-6 (IL-6), CAFs secrete growth factors and promote epithelial-mesenchymal transition (EMT) -- a process by which cancer cells gain the ability to migrate and invade other tissues.
AR signaling controls CAF behavior as well, inducing the secretion of TGF-beta, which enhances tumor cell invasiveness and drug resistance. CAFs also create a physical barrier that limits drug delivery to the tumor, contributing directly to treatment failure.
Adipocytes (fat cells) in and around prostate tissue can be transformed into malignant adipocytes that release fatty acids and lipid metabolites, providing an energy source that fuels cancer cell growth and metastasis. ECM stiffening caused by continuous stromal remodeling activates PI3K/Akt and MAPK pathways, further driving aggressive tumor behavior.
Emerging research reveals that microorganisms -- including bacteria and viruses -- inhabit prostate tissue and the gut, and both can influence prostate cancer development and treatment response. This is an area of rapidly growing scientific interest.
Gut microbiota can produce androgens by metabolizing precursor molecules, potentially undermining androgen deprivation therapy even in patients actively receiving it. Specific bacterial species have been linked to treatment response: patients responding to enzalutamide (a hormone therapy) showed higher levels of Streptococcus salivarius, and responders to PD-1 immunotherapy had higher levels of a bacterium called Akkermansia muciniphila.
Bacteria found within prostate tissue itself, including Propionibacterium acnes and Escherichia coli, can trigger inflammatory pathways and induce epigenetic changes in cancer cells. Ruminococcus, enriched in CRPC patients, is associated with altered phospholipid metabolism -- a sign that microbiome composition may reflect or drive disease progression.
Viruses including HPV (human papillomavirus), EBV (Epstein-Barr virus), and HHV (human herpesvirus) have been detected in prostate cancer tissue. HPV-16 increases prostate cancer risk (odds ratio 1.61), and its E6 and E7 proteins disrupt tumor suppressor proteins p53 and Rb, destabilizing cell cycle control and potentially facilitating cancer development.
Within prostate cancer cells, specific signaling pathways serve as master regulators of growth, immune evasion, and treatment resistance. Two of the most important are the Wnt/beta-catenin and PI3K/Akt/mTOR pathways.
The Wnt/beta-catenin pathway controls cancer stem cell self-renewal, enabling a small population of treatment-resistant cells to regenerate the tumor after therapy. It also regulates cell adhesion and migration, promotes immune escape by suppressing anti-tumor immune responses, and drives angiogenesis by stimulating endothelial cell proliferation.
The PI3K/Akt/mTOR pathway is frequently hyperactivated in CRPC. It promotes cancer cell metabolism and survival, induces inflammatory responses in the TME, enhances PD-L1 expression to suppress immune cells, and drives angiogenesis through VEGF upregulation. As prostate cancer progresses to CRPC, it often shifts dependence from AR signaling to this pathway, making PI3K/Akt/mTOR inhibition a compelling therapeutic target.
The transcription factor NF-kB acts as a key regulator of inflammation and immune evasion in the prostate tumor microenvironment. It activates pro-inflammatory cytokines including TNF-alpha, IL-6, and IL-1beta, and promotes PD-L1 expression, helping cancer cells evade T cell surveillance and persist within the TME.
A deeper understanding of the tumor microenvironment is opening new avenues for both earlier diagnosis and more targeted treatment. Microenvironmental biomarkers -- measurable molecules that reflect what is happening inside and around the tumor -- include ECM proteins, cancer stem cell markers, cytokines, growth factors, and metabolites detectable in blood or tissue.
Key diagnostic targets include matrix metalloproteinases (MMPs) that indicate tumor invasiveness, interleukins such as IL-6 and IL-8 that reflect TME inflammation, VEGF and FGF levels reflecting angiogenic activity, and chemokines like CXCL12 involved in cancer cell migration. Analyzing extracellular vesicles -- tiny particles secreted by cancer cells -- offers a minimally invasive route to detecting these markers.
On the treatment front, immune checkpoint inhibitors targeting PD-L1/PD-1 have shown promise, particularly for treatment-resistant cases, and combining them with anti-angiogenic therapy targeting VEGF can overcome the limitations of either approach alone. Nanoparticles and oncolytic viruses are being developed to deliver drugs that can penetrate the physical barriers of the tumor stroma.
Modulating the gut microbiome -- for example through fecal microbiota transplantation from immunotherapy responders -- represents an emerging strategy to improve treatment response. Because different patients have radically different microenvironment profiles, personalized approaches integrating genomic, metabolomic, and microbiome data are essential to match patients with the treatments most likely to work for their specific tumor ecosystem.