According to the United States (US) Census Bureau, the number of veterans in the US in 2018 was around 19.9 million. Nine out of 10 were males, and 33% were between 50-69 years old, an age group that is at the highest risk for prostate cancer (PCa). The VA Central Cancer Registry consistently shows that PCa is the most frequently diagnosed cancers among male veterans, accounting for >30% of the approximately 50,000 cancer diagnoses. There is growing concern that environmental and/or occupational exposure to metal ions during deployment and post-deployment increases PCa risk in veterans. The International Agency for Cancer Research classified inorganic arsenic (iAs) as a carcinogen, while lead (Pb) is a potential carcinogen in humans. Pb exposure is a known hazard of military service, while data for iAs exposure is less well-established. Further, wide-spread exposure to these metal ions in veterans could be mediated through inhalation, ingestion, and dermal adsorption of toxic smoke from burning oil fields and waste disposal burn-pits. iAs and/or Pb exposure have been considered potential risk factors for PCa, but the underlying mechanism is largely undefined. In a small clinical study, we found that iAs and Pb levels were significantly higher in the urine of PCa patients compared to controls. Using our new 2-hit animal model, we found that exposure to iAs or Pb increased (1) PCa risk in vivo and (2) the ability of prostate epithelial stem-like cells (PrESLCs) isolated from treated animals to form colonies in soft agar, a hallmark of cellular transformation. In this animal model, a 1-month metal treatment followed by chemical carcinogen treatment significantly increased the incidence of PCa and pre-cancerous lesions in iAs-treated mice, with similar trends in Pb-treated animals. Importantly, single-cell RNAseq analyses revealed that Pb was associated with the expansion of a subpopulation of PrESLCs with epithelial lineage markers into stroma-like oncogenic cells, while iAs was associated with the emergence of a rare, unique subpopulation of oncogenic PrESLCs similar to “cancer” stem cells. This proposal will test the hypothesis that iAs and/or Pb dysregulate specific, and likely different, signaling pathways in subpopulations of PrESLCs to initiate or increase the risk of carcinogenesis in the prostate. This is an untested hypothesis in the field of prostate carcinogenesis and in military veterans’ health. Two Aims are proposed. Aim 1: Determine the carcinogenic potential of metal treated PrESLCs in vivo using a renal grafting model of PCa formation. We will evaluate the effects of metals on the formation of PCa in vivo in immune-deficient host mice, either with or without chemical induction of PCa. Aim 2: Characterize stem-like cells with metal-specific transcriptomic signatures. We will use single-cell RNAseq and visualization informatics to identify the unique gene signatures that characterize rare subpopulations of metal-induced cancer stem ce...