Abstract BACKGROUND: Like many cancers, prostate cancer (PCa) relies on tissue- and lineage-specific transcription factors essential for normal tissue function and tumor progression. A key master factor is the androgen receptor (AR), which regulates prostate tissue identity and differentiation, maintaining normal, growth-suppressive, prostate-specific luminal programs via androgen response elements (AREs). However, during tumorigenesis, AR is co-opted to drive oncogenic transcription programs, including the reprogramming factors like FOXA1 and HOXB13. Despite AR’s critical role, the mechanisms and functional implications of both its oncogenic and growth-suppressive programs in PCa remain incompletely understood. We hypothesized that the previously known methyl-CpG reader and DNA repair protein, MBD4, safeguards these lineage trajectories by restraining pioneer factor engagement. METHODS: We performed an epigenetic-focused CRISPR screen (2,508 genes) in an LNCaP ARE-activated model to nominate the regulators of AR programs. We engineered MBD4 knockout and inducible overexpression models and profiled chromatin and transcription by ATAC-seq; CUT&RUN (AR, FOXA1, H3K27ac, H3K4me3, H3K27me3); and RNA-seq across AR+ and AR- lines. Proliferation and lineage-identity programs were also evaluated in normal mouse prostate organoids. Clinical relevance was assessed using multi-cohort patient transcriptomes and cancer-dependency datasets. RESULTS: MBD4 emerged as a gatekeeper of the AR/ARE-mediated growth-suppressive program. MBD4 loss increased chromatin accessibility and enhancer acetylation at FOXA1-enriched loci, with FOXA1 binding expanding upon loss and decreasing with MBD4 overexpression. MBD4 localized to AR/FOXA1 enhancers and limited FOXA1 engagement. Functionally, MBD4 knockout accelerated proliferation in AR+ lines (e.g., LNCaP, MDA-PCa-2b) and slowed growth in AR- lines (e.g., PC3, DU145). In normal mouse prostate organoids, MBD4 disruption biased luminal epithelial identity programs and reprogrammed enhancer architecture. Across patient cohorts, MBD4 expression and dependency patterns tightly tracked with AR status/lineage, linking lineage context to chromatin plasticity. CONCLUSIONS: MBD4 acts as a gatekeeper of the AR/ARE-mediated growth-suppressive program by limiting lineage-specific enhancers and restraining FOXA1 engagement. Loss of MBD4 promotes FOXA1-driven reprogramming and lineage plasticity, nominating the MBD4-FOXA1 axis as a potential therapeutic target. AI DISCLOSURE: Generative AI was used to help draft the wording of this abstract; all content was supplied, reviewed, and approved by the authors. Citation Format: Xuanrong Chen, Janny Alexander Villa-Pulgarin, Jiansheng Wu, Un In Chan, Aaron Orgel, Jude Owiredu, Anjali Yadav, Andrea Sboner, Christopher E. Barbieri. MBD4 regulates FOXA1 lineage-specific enhancers to promote prostate tumorigenesis and progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 4062.

Supplementary Figure S5. Immunostaining of tissues excised from prostate tumor regions.

Supplementary Table S1. Bootstrap-based 95% confidence bounds for MMUS1469 migration counts and seeding topologies for all clonal populations (CPs). Supplementary Table S2. Bootstrap-based 95% confidence bounds for MMUS1495 migration counts and seeding topologies for all clonal populations (CPs).

Supplementary Figure S1. Validation of EvoCaP platform in vitro. Supplementary Figure S2. BC10 exhibited robust editing efficiency in vitro. Supplementary Figure S3. Technical markers to identify tumor cells are present in organs. Supplementary Figure S4. Consistent bioluminescence and fluorescence imaging of tissues from EvoCaP mice.

Acquired resistance to androgen receptor (AR)-targeted therapies and the progression to metastatic-castrate resistant prostate cancer (CRPC) remains a significant clinical problem. Mechanisms of acquired resistance include lineage plasticity, by which CRPC tumors can become AR-negative and progress to neuroendocrine prostate cancer (NEPC). Clinical prognoses for patients with NEPC are poor and more work is needed to understand the underlying molecular mechanisms driving lineage plasticity and CRPC to NEPC progression. FOXA2, a key lineage-determining pioneer transcription factor (TF), is significantly upregulated in subsets of CRPC and the majority of NEPC patient tumors. However, little is known about the role of FOXA2 in regulating lineage plasticity and progression from CRPC to NEPC. We queried single-cell RNAseq data from CRPC patient tumors and performed RNAseq and immunohistochemical assessment in patient tumors from 2 independent cohort of patient tumors. In CRPC and NEPC patient-derived organoids, we assessed transcriptional, chromatin accessibility changes and TF/pioneer factor and SWI-SNF chromatin occupancy changes. We performed unbiased approach of rapid immunoprecipitation mass spectrometry of endogenous protein for FOXA2 in adenocarcinoma and NEPC models to identify chromatin-bound, FOXA2-interacting proteins. We validated FOXA2-co-factor protein-protein interacting using co-immunoprecipitation. Lastly, we generated knock-in degron alleles for FOXA2 in NEPC patient-derived organoids to understand how FOXA2 is required for NEPC maintenance. In the CRPC tumors, high FOXA2 expression was correlated with high ONECUT2 and SOX2 expression, high NEPC score, low AR signaling score, and poorer patient prognosis. We also found that FOXA2 overexpression suppressed androgen signaling and reprograms the chromatin accessibility landscape to close AR binding sites and open chromatin related to neural reprogramming. Additionally, we found that FOXA2 interacts with the SWI-SNF complex, AR, and HOXB13 to redirect AR and HOXB13 DNA binding away from canonical AR-regulated sites. We found that FOXA2 is bound at regulatory regions of known NEPC driver genes and epigenetic modifiers. Lastly, we discovered that FOXA2 physically interacts with key NEPC TFs and epigenetic regulators, suggesting that these FOXA2 physical interactions are required for NEPC progression. Loss of FOXA2 was sufficient to suppress key NEPC genes. Overall, our data from murine and human models indicate that FOXA2 functions to suppress androgen signaling by redirecting AR and AR cofactor binding. Our data also shows that FOXA2 functions as a pioneer TF to redirect chromatin accessibility and, through its interaction with key NEPC-associated TFs and a chromatin-modifying protein complex, drives the NEPC-associated molecular program. These findings provide novel mechanistic insights underlying how FOXA2 regulates lineage plasticity and NEPC progression. Richard Garner, Nicholas Brady, Xuanrong Chen, Alessandra Ferri, Richa Singh, Kate Dunmore, Filippo Pederzolli, Hubert Pakula, Jagpreet Singh Nanda, Michael Freeman, Michael Haffner, Colm Morrissey, Brian Robinson, Antonio Marzio, Massimo Loda, Christopher Barbieri, David S. Rickman. FOXA2 reprograms AR signaling to promote lineage plasticity in advanced prostate cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Innovations in Prostate Cancer Research and Treatment; 2026 Jan 20-22; Philadelphia PA. Philadelphia (PA): AACR; Cancer Res 2026;86(2_Suppl):Abstract nr PR033.

Supplementary Figure S6. Barcode design and analysis. Supplementary Figure S7. Analysis and simulation barcode data to evaluate EvoTraceR performance. Supplementary Figure S8. Pipeline for detecting and calling edits in barcode. Supplementary Figure S9. Temporal accumulation of barcode edits in vivo. Supplementary Figure S10. Eco-statistical analysis of MMUS1495. Supplementary Figure S11. Metastatic trajectories for EvoCaP mouse cohorts. Supplementary Figure S12. Organ diversity between EvoCaP mice. Supplementary Figure S13. Expansion of EvoCaP platform in vitro.

The prostate cancer (PCa) tumor microenvironment (TME) is enriched in myeloid cells that drive progression and therapy resistance. Tumor-associated macrophages (TAM) can promote tumor growth by suppressing antitumor immunity. We have previously shown that stereotactic body radiotherapy (SBRT) induces inflammatory remodeling of the PCa TME with enrichment of a population of radiation-induced TREM2+ TAM. Herein, we characterize the immunological impact of TREM2-expressing TAM on intratumoral T-cell function and explore the therapeutic potential of TREM2 blockade in the context of radiotherapy. We performed 10x scRNA-seq on prostatectomy specimens from high-risk PCa patients treated with preoperative SBRT or non-irradiated controls. THP-1 and bone marrow–derived macrophages (BMDMs) were used to assess radiation-induced immune response. In vivo studies in C57BL/6 mice bearing PTEN-/-SPOPmutCHD1del organoid-derived or B6CaP flank tumors assessed immune changes after SBRT. Anti-TREM2 mAb treatment +/- SBRT was used to evaluate the immune remodeling of the TME. scRNA-seq analysis of human samples revealed enrichment of a myeloid cluster expressing a damage-associated macrophage signature (Trem2, Apoe, Spp1, Lgals3) in SBRT-treated versus controls (35.6% vs 5.7%). Irradiation increased TREM2 expression in BMDMs (p<0.01) and THP-1 cells under M0 and TAM-like conditions. When co-cultured with irradiated (vs. non-irradiated) BMDM-M0 cells, CD8+ T-cells demonstrate a decrease in CD8+ T-cell proliferation (p<0.012) and IFN-γ production (p<0.0005). Further, CD8+ T-cells co-cultured with TREM2hi TAMs (vs. TREM2lo) from irradiated organoid PCa tumors demonstrated a higher proportion of T-cells expressing Tim-3+ (p<0.001) and PD-1+ (p<0.01), suggesting that TREM2hi TAMs may induce a terminally exhausted phenotype in CD8+ T-cells. In vivo studies demonstrated that SBRT reduces tumor volume and was associated with a corresponding increase in intra-tumoral density of TREM2+ TAMs and FoxP3+ regulatory T-cells (Tregs) (p<0.008) in both organoid-derived PCa and B6CaP flank models. Tumor lysate from irradiated tumors demonstrated elevated soluble TREM2 (p < 0.028) and TGF-β1 (p < 0.034) levels. scRNA-seq of irradiated and non-irradiated organoid-derived flank tumors confirmed a radiation-induced anti-inflammatory TAM program (Arg1, Mrc1, Msr1, Tgfbi), corroborating our human PCa data. The combination of TREM2 blockade and SBRT remodeled the TME with a reduction in the density of intratumoral FoxP3+ Tregs and reduced Treg:Teff ratio as well as fewer TAMs expressing Arg1 and TGF-β1, collectively suggesting abrogation of SBRT-induced immunosuppression. Our findings in irradiated human PCa and subsequent validation studies in preclinical PCa models suggest that SBRT promotes a TREM2-driven anti-inflammatory macrophage program that remodels the immune TME. TREM2 blockade represents a potential strategy to reverse immune suppression and promote anti-tumor immunity when combined with SBRT. Janny A. Villa-Pulgarin, Un In Chan, Jiansheng Wu, Fabio Socciarelli, Jeffrey Kraynak, Sidney Wolfe, Hubert Pakula, Luigi Marchionni, Francesca Khani, Massimo Loda, Himanshu Nagar, Christopher Barbieri, Ariel E. Marciscano. Radiotherapy remodels the tumor microenvironment via a TREM2-associated macrophage program that can be therapeutically targeted with TREM2 blockade [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Innovations in Prostate Cancer Research and Treatment; 2026 Jan 20-22; Philadelphia PA. Philadelphia (PA): AACR; Cancer Res 2026;86(2_Suppl):Abstract nr A069.

Like many cancers, prostate cancer (PCa) relies on tissue- and lineage-specific transcription factors essential for normal tissue function and tumor progression. A key master factor is the androgen receptor (AR), which regulates prostate tissue identity and differentiation, maintaining normal, growth-suppressive, prostate-specific luminal programs via androgen response elements (AREs). However, during tumorigenesis, AR is co-opted to drive oncogenic transcription programs, including reprogramming factors like FOXA1 and HOXB13. Despite AR’s critical role, the mechanisms and functional implications of both its oncogenic and growth-suppressive programs in PCa remain incompletely understood. We hypothesized that the methyl-CpG reader and DNA repair protein MBD4 safeguards lineage trajectories by restraining pioneer factor engagement. We performed an epigenetic-focused CRISPR screen (2,508 genes) in an LNCaP ARE-activated model to nominate the regulators of AR programs. We engineered MBD4 knockout and inducible overexpression models and profiled chromatin and transcription by ATAC-seq; CUT&RUN (AR, FOXA1, H3K27ac, H3K4me3, H3K27me3); and RNA-seq across AR+ and AR- lines. Proliferation and lineage-identity programs were also evaluated in normal mouse prostate organoids. Clinical relevance was assessed using multi-cohort patient transcriptomes and cancer-dependency datasets. MBD4 emerged as a gatekeeper of the AR/ARE-mediated growth-suppressive program. MBD4 loss increased chromatin accessibility and enhancer acetylation at FOXA1-enriched loci, with FOXA1 binding expanding upon loss and decreasing with MBD4 overexpression. MBD4 localized to AR/FOXA1 enhancers and limited FOXA1 engagement. Functionally, MBD4 knockout accelerated proliferation in AR+ lines and slowed growth in AR- lines (e.g., PC3, DU145). In normal mouse prostate organoids, MBD4 disruption biased luminal epithelial identity programs and reprogrammed enhancer architecture. Across patient cohorts, MBD4 expression and dependency patterns tightly tracked with AR status/lineage, linking lineage context to chromatin plasticity. MBD4 acts as a gatekeeper of the AR/ARE-mediated growth-suppressive program by limiting lineage-specific enhancers and restraining FOXA1 engagement. Loss of MBD4 promotes FOXA1-driven reprogramming and lineage plasticity, nominating the MBD4–FOXA1 axis as a potential therapeutic target. AI DISCLOSURE: Generative AI was used to help draft the wording of this abstract; all content was supplied, reviewed, and approved by the authors. Xuanrong Chen, Janny Villa-Pulgarin, Jiansheng Wu, Un In Chan, Jude Owiredu, Anjali Yadav, Andrea Sboner, Christopher Barbieri. MBD4 regulates FOXA1 lineage-specific enhancers to promote prostate tumorigenesis and progression [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Innovations in Prostate Cancer Research and Treatment; 2026 Jan 20-22; Philadelphia PA. Philadelphia (PA): AACR; Cancer Res 2026;86(2_Suppl):Abstract nr A010.

Enhanced cholesterol synthesis and lipid droplet accumulation are hallmarks of aggressive prostate cancer, yet how tumour cells sense metabolic inputs to dynamically regulate cholesterol homeostasis remains poorly defined. Here we uncover a metabolic signalling mechanism in which prostate cancer cells remodel propionyl-CoA metabolism to support stress adaptation during disease progression. We show that the catabolism of branched-chain amino acid, specifically isoleucine and valine, is the primary source of intracellular propionyl-CoA in prostate cancer cells. Beyond its metabolic role, propionyl-CoA functions as a signalling molecule that stabilizes nuclear sterol regulatory element-binding protein 2 (SREBP2) through site-specific lysine propionylation, thereby enhancing its transcriptional activity. This activation promotes cholesterol biosynthesis, fuels de novo androgen production, and sustains androgen receptor signalling under metabolic and therapeutic stress, including androgen deprivation. Together, our findings establish propionyl-CoA as a key metabolic signal linking amino acid catabolism to cholesterol-driven oncogenic programmes and highlight targeting isoleucine and valine metabolism as a potential strategy to disrupt lipid reprogramming in prostate cancer.

Background Irreversible electroporation (IRE) is a nonthermal local therapy for prostate cancer (PCa). However, the feasibility, outcomes, and safety of reduced-dose radiation therapy (RT) following IRE (RTIRE) for the treatment of intermediate-risk PCa are unknown. Purpose To assess the feasibility of RTIRE for the treatment of intermediate-risk PCa. Materials and Methods This was a prospective study from May 2022 to April 2024 and included participants with intermediate-risk PCa with a focal index lesion (grade group 2 or 3 disease) visible at MRI. Participants underwent RTIRE (to 32.5 Gy in five fractions) with follow-up at 3, 6, 9, and 12 months. The primary end point was enrollment feasibility. Secondary end points included early oncologic control, quality-of-life outcomes, and adverse events. The Wilcoxon rank-sum test was used to compare continuous values at different time points. Results A total of 10 men (median age, 66 years [IQR, 61-72 years]) successfully completed RTIRE. At 12 months, no residual disease was detected at biopsy in 100% (10 of 10) of participants. Median prostate-specific antigen level decreased from baseline (7.65 ng/mL) to 3 months (0.98 ng/mL; P = .002) and remained stable at 12 months (0.56 ng/mL; P = .002 vs baseline). Median Expanded Prostate Cancer Index Composite for Clinical Practice score increased from baseline (3.5 [IQR, 3-8]) to 6 months (13 [IQR, 9-19]; P = .02), returning to near baseline at 12 months (6 [IQR, 5-15.75]; P = .05). International Index of Erectile Function score decreased from baseline (median, 23.5) to 6 months (median, 12; P = .02), with recovery by 12 months (median, 22; P = .16 vs baseline). Median International Prostate Symptom Score was stable at 12 months (P = .56 vs baseline). No severe adverse events occurred (100% [27 of 27] of adverse events were grade 1 or 2). Conclusion Treatment of participants with intermediate-risk PCa with RTIRE was feasible and showed no clinically meaningful decline in patient-reported outcomes and no severe adverse events. Clinical trial registration no. NCT05345444 © RSNA, 2026 Supplemental material is available for this article. See also the editorial by Nezami and Unger in this issue.

The biological mechanisms underlying the cooperation between germline genetic variants and somatic mutations during carcinogenesis are rarely elucidated. In this study, characterizing isogenic prostate cancer cell lines, we dissected the interplay between a germline variant at the 7p14.3 locus (rs1376350, G>A) and early recurrent prostate cancer-specific mutation in the speckle-type POZ protein (SPOP) gene across human prostate adenocarcinomas. The transcriptomes of multiple edited models pointed to GLI3 and the Hedgehog signaling pathway in a genotype-specific manner, whereas SPOP mutation and androgen receptor stimulation promote GLI3 accumulation in the full-length, transcriptionally active form. This, in turn, triggers the cell-autonomous production of steroids that prostate cancer relies on, in line with the enhanced responsiveness of SPOP-mutated prostate cancer to androgen deprivation therapy. These data demonstrate that germline variants dictate prostate cancer somatic evolution and suggest opportunities to jointly model germline-somatic relationship to help untangle the complexity of human cancer. SIGNIFICANCE:Significant heritability is observed for common cancer types worldwide. The molecular mechanisms by which inherited genetics facilitate cancer initiation might transit through its cooperation with specific somatic events that then dictate the tumor features. Through a germline-somatic tandem leading to steroid biosynthesis, we suggest a paradigm to study cancer initiation.

e17164 Background: Prostate cancer (PC) is the most common cancer among men in the U.S. Compared to Caucasians, Black men have a higher PC incidence, are diagnosed at a younger age, and have a higher PC specific mortality. The reasons for this disparity are multi-faceted and include genetic and socioeconomic factors including access to care. Recent PSA screening guidelines recommend screening in Black men from the age of 40. However, studies suggest uptake of this PSA screening recommendation is very low. Development of a low-cost and rapid screening tool that could be performed in the community could increase PSA testing among Black men. Methods: We developed a total PSA (tPSA) POC lateral flow assay test strip that utilizes immunochromatography to yield different signal intensities based on tPSA concentrations and uses a commercial portable strip reader (Cube) to quantify PSA based on the ratio of signal intensity of test and control line (TC ratio). In an IRB approved study, men undergoing standard PSA testing with a PSA 0.1-20 ng/ml enrolled on protocol after providing informed consent. 50 µL of fingerstick collected blood was mixed with 150 µL of buffer (PBS 1X, 1% BSA, 1% Tween-20) and 100 µL deposited in the chip well and the TC ratio read at 20 min and correlated with a venous blood drawn PSA measured in a CLIA lab. Spearman correlation coefficient was used to assess the correlation between the values of the two tests, and a receiver-operating characteristic curve (ROC) analysis was performed to find the optimal cutoff of TC test to maximize its Sensitivity and Specificity using Youden’s index with a PSA test (dichotomized at 4) as the gold standard. Results: PSA values were plotted against the TC values in a scatter plot from 30 men. The Spearman correlation coefficient between fingerstick and venous PSA was 0.89 (95% CI: 0.78, 0.96). Using a dichotomized approach where a PSA < 4 was Negative, >4 Positive, a ROC analysis demonstrated an AUC of 0.98 (95% confidence interval [CI]: 0.94, 1), with a sensitivity of 85% (95% CI: 62.1% - 96.8%), and specificity of 100% (95% CI: 69.2% - NA). A second cohort of 23 men using a different batch of POC test strips similarly demonstrated an AUC of 0.97 (95% CI: 0.93, 1) with a sensitivity of 86.7% (95% CI: 59.5% - 98.3%), and specificity of 100% (95% CI: 63.1% - NA). Conclusions: Our data show that a PSA POC test is feasible and accurate as a screening test to detect PSA > 4 ng/ml. Patients with positive tests may be referred to the appropriate healthcare provider for further evaluation. PSA POC testing is an alternative and convenient low-cost method to test for elevated PSA in a community setting and improve access to care. This will be further tested by utilizing the device for PSA screening in the community at barbershops.

BACKGROUND AND OBJECTIVE:Some patients undergoing prostatectomy develop biochemical recurrence or have persistently detectable prostate-specific antigen level. Salvage radiotherapy (RT), delivered over ≥4 wk, is a current standard of care. Our objective was to demonstrate that salvage RT delivered in a five-fraction stereotactic body radiotherapy (SBRT) regimen does not significantly increase patient-reported genitourinary (GU) and gastrointestinal (GI) symptoms compared with a 20-fraction regimen (HYPO). METHODS:In this randomized noninferiority study, 137 patients were randomized 1:1 to salvage RT with 32.5 Gy in five fractions or 55 Gy in 20 fractions. We report acute changes in Expanded Prostate Cancer Index Composite (EPIC) scores and Common Terminology Criteria for Adverse Events at 3 and 6 mo. KEY FINDINGS AND LIMITATIONS:The difference in the changes in EPIC GU scores between SBRT and HYPO was 3.3 (95% confidence interval [CI], -8.53, 1.93), indicating a lack of a clinically meaningful difference. The difference in the changes in EPIC GI scores between SBRT and HYPO was 1.16 (95% CI, -5.15, 7.46), indicating a lack of a clinically meaningful difference. CONCLUSIONS AND CLINICAL IMPLICATIONS:Salvage RT delivered in five fractions was not associated with a significantly worse decline in patient-reported GU or GI toxicities at 3 or 6 mo. Further follow-up is necessary to monitor for potential differences in late toxicity and patient-reported outcomes.

Supplementary Fig. S3. Original unedited IB images for representative Western blots experiments (n-3) used in Figure 3A.

Mutations that accumulate in the human male germline with age are a major driver of genetic diversity and contribute to genetic diseases. However, aging-related male germline mutation rates have not been measured directly in germline cells (sperm) at the level of individuals. We developed a study design in which we recalled 23 sperm donors with prior banked samples to provide new sperm samples. The old and new sequential sperm samples were separated by long timespans, ranging from 10 to 33 years. We profiled these samples by high-fidelity duplex sequencing and demonstrate that direct high-fidelity sequencing of sperm yields cohort-wide mutation rates and patterns consistent with prior family-based (trio) studies. In every individual, we detected an increase in sperm mutation burden between the two sequential samples, yielding individual-specific measurements of germline mutation rate. Deep whole-genome sequencing of sequential sperm samples from two individuals followed by targeted validation measured remarkably stable mosaicism of clonal mutations that likely arose during embryonic and germline development, suggesting that age did not substantially impact the diversity of spermatogonial stem cell pools in these individuals. Our application of high-fidelity and deep whole-genome sequencing to sequential sperm samples provides insight into aging-related mutation processes in the male germline.

Many chemotherapeutic agents impair cancer growth by inducing DNA damage. The impact of these agents on mutagenesis in normal cells, including sperm, is largely unknown. Here, we applied high-fidelity duplex sequencing to 94 samples from 36 individuals exposed to diverse chemotherapies and 32 controls. We found that in many of the sperm samples from men exposed to chemotherapy, the mutation burden was elevated as compared with controls and the expected burden based on trio studies, with 1 patient having a more than 10-fold increase over that expected for age. Saliva from this same individual also had a markedly higher mutation burden. We then validated this finding using other tissues, also finding an increased mutation burden in the blood and liver of many patients exposed to chemotherapy as compared with unexposed controls. Similarly, mice treated with 3 cycles of cisplatin had an increased mutation burden in sperm but also in the liver and hematopoietic progenitor cells. These results suggest an association between cancer therapies and mutation burden, with implications for counseling patients with cancer considering banking sperm before therapy and for cancer survivors considering the trade-offs of using banked sperm as compared with conceiving naturally.