A cross-sectional study of the association of dental health factors with progression and all-cause mortality in men diagnosed with HPV-associated oropharyngeal cancer

BACKGROUND

Human Papillomavirus-associated oropharyngeal cancer (HPV-OPC) incidence is increasing among men in the United States. Poor dental health has previously been associated with risk of head and neck cancers, oral HPV infection, and persistence but it is not understood whether dental health is associated with outcomes. We sought to determine the association of dental health with progression free survival and overall mortality among men with an HPV-OPC.

METHODS

A cross sectional study of men diagnosed with HPV-OPC between 2014-2020 at Moffitt Cancer Center in Tampa, FL was conducted. Dental records were abstracted for assessment of dental fitness prior to cancer treatment. Five dental factors including number of teeth lost, pocket depth, gingival score, loss of attachment, and bone loss were individually examined. Risk factor and outcome data were collected from a patient risk questionnaire and medical record. Using item response theory, an overall dental fitness score from five dental factors was developed in which missing data were multiply imputed. Cox proportional hazards model was used to assess whether dental factors were associated with progression-free survival or overall mortality.

RESULTS

Among 206 HPV-OPC cases, median follow-up was 3.4 years (IQR: 2.4-4.4) during which 40 cases involved progression or mortality and 25 deaths occurred. Overall dentition was significantly associated with progression free survival (p = 0.04) and with overall survival (p = 0.03) though findings were not significant after adjustment for age at diagnosis, stage, and smoking history (p = 0.146 and p = 0.120, respectively). A pocket depth of 7 mm or more was associated with overall survival (HR: 5.21; 95% CI: 1.43-19.11) and this remained significant after adjustment for confounding (aHR: 4.14; 95% CI: 1.72-16.26).

CONCLUSIONS

Among men diagnosed with an HPV-associated OPC in the US, worse dental health was associated with reduced progression free survival and overall survival, but not after adjustment for confounders. Further studies are needed to examine whether dental health is associated with other prognostic factors and subsequent treatment-related outcomes.

Effects of prexasertib, a CHK1 inhibitor, in the immune microenvironment of head and neck squamous cell carcinoma (HNSCC)

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Background: Despite considerable advancements in the standard therapies including surgery, chemotherapy and radiotherapy, the clinical outcome for head and neck squamous cell carcinoma (HNSCC) remains poor due to tumor recurrence and metastasis. Molecular-targeted therapies have evolved as novel and promising treatment for HNSCC patients. Herein, we identified a CHK1 inhibitor, prexasertib, as a therapeutic target that enhanced the infiltration of innate and adaptive immune markers in the mice tumor immune microenvironment (TIME) and subsequently sensitizes the tumors. Methods: For this study we used syngeneic mouse model of HNSCC developed using mouse tonsil epithelial cells transformed with HRAS expression and PTPN13 knockdown to represent tobacco-induced HNSCC (MTE-Ras). In vitro drug activity of prexasertib was determined using immunoblotting, flow cytometry, cell proliferation and colony formation assays. The effect of prexasertib on TIME was quantified by Quantigene Plex panel and multiplex immunohistochemistry (mIHC). Results: We found that in vitro treatment with prexasertib increased the amount of DNA damage in the cancer cells and eventually lead to their death. Similarly, our in vivo data showed that treatment with prexasertib resulted in significant tumor regression and increased mice survival. At the molecular level, prexasertib treatment resulted in an upregulation of transcripts associated with T-cell activation, cytokines, chemokines and macrophages indicating an upregulation of inflammatory gene signature. This was further supported by our findings from mIHC staining of mice tumors showing increased infiltration of natural killer cells, natural killer T cells and dendritic cells, following prexasertib treatment. Interestingly, we also saw an increase in the Tregs after prexasertib treatment, which is indicative of an immunosuppressive environment, and we speculate this could be as a result of negative feedback following immune activation by prexasertib treatment. Conclusions: Our results uncover a previously unidentified role of prexasertib in regulating the innate and adaptive immune response in HNSCC, and therefore further corroborate CHK1 as a promising therapeutic target in HNSCC.

Abstract 5314: Smad4 loss upregulates chemokine expression and promotes tumor inflammation and growth in head and neck cancer

Background: Head and neck squamous cell carcinoma (HNSCC) is the 6th most common cancer worldwide. Of the patients diagnosed with HNSCC, previous findings show that SMAD4 loss is more common in recurrent HNSCC patients compared with newly diagnosed cases and is strongly associated with poor patient survival and metastases. SMAD4 is a tumor suppressor gene and is a central mediator of the transforming growth factor β (TGF-β) signaling pathway and acts as a co-SMAD which binds receptor-regulated SMADs such as SMAD2 and 3. SMAD2/3/4 complex is important for regulating downstream gene transcription that is involved in tumor invasion and metastasis.

Purpose: Since the TGF-β pathway is highly dysregulated in HNSCC, we investigate in this study how SMAD4 downregulation alters TGF-β pathway signaling and the tumor microenvironment.

Results: Using isogenic HNSCC cell lines, we visualized using immunofluorescence staining that levels of activated phospho-SMAD2 in the nucleus are correlated with expression of SMAD4. Genome-wide screening using Gene Set Enrichment Analysis (GSEA) further revealed changes in gene expression during SMAD4 knockdown in HNSCC cells. From GSEA results, the 20 most significantly altered Gene Ontology (GO) pathways were determined. It was shown that majority of these GO pathways are associated with regulating neutrophil migration and chemotaxis with an upregulation of CXC chemokine gene expression, specifically with CXCL1. In contrast, anti-tumor chemokines, such as CXCL9 and CXCL11, were downregulated during loss of SMAD4 expression. Using an orthotopic mouse model we show that in vivo, decreased expression of SMAD4 promotes tumor take and growth.

Conclusion: Collectively, these results suggest that HNSCC tumors with SMAD4 loss may have poor prognosis attributed to immunosuppressive functions of chemokine expression that acts on tumor-associated neutrophils.

Citation Format: Jude Masannat, Xuefeng Wang, Biwei Cao, FeiFei Song, Ritu Chaudhary, Janis de la Iglasia, Ciaara Gorgoglione, Robbert Slebos, Christine Chung. Smad4 loss upregulates chemokine expression and promotes tumor inflammation and growth in head and neck cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5314.

A phase II study of capecitabine (Cape) or 5-fluorouracil (5-FU) with pegylated interferon alpha-2b (Peg-IFNA-2b) in unresectable/metastatic cutaneous squamous cell carcinoma (CSCC)

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Background: Patients (pts) with unresectable/metastatic CSCC have a poor prognosis, and until recently had limited treatment options. Based on encouraging efficacy in case report series, we conducted a phase 2 trial to evaluate the efficacy of CAP or 5-FU in combination with Peg-IFNA-2b in advanced CSCC. Methods: Eligible pts with measurable unresectable/metastatic CSCC were treated with CAP (1000mg/m2 PO twice daily days 1-14) or 5-FU (800 mg/m2 IV days 1-4), and Peg-IFNA-2b (subcutaneously at 3ug/kg weekly) in a 21-day cycle for up to 9 cycles, intolerable toxicity or progression. The primary objective was to assess overall response rate (ORR) while secondary objectives were safety and survival. Exploratory correlative tissue immune markers were studied using multiplex immunohistochemistry (mIHC) on pre- and post-treatment optional tumor biopsies. Results: Poor accrual led to early study closure after enrolling 8 pts. All pts were male, median age was 73.5 yrs. The ORR was 25% (1 CR, 1 PR); 4 pts had SD, 1 with PD and 1 withdrew consent prior to first restaging. The pt with CR had previously progressed on anti-PD1 therapy; tissue mIHC from this pt showed an increase in CD8+ cells prior to starting trial therapy. Due to the low sample size the 6 and 12-month survival estimates for OS and PFS are the same, 87.5% and 50% for 6 and 12 months respectively. Grade ≥ 3 or higher toxicities included decreased WBC (n = 3), fatigue, failure to thrive, anemia (all n = 2), and neutropenia, dehydration, hand-foot syndrome (all n = 1). Dose reductions were frequently encountered. Conclusions: Combination CAP/5-FU plus Peg-IFNA-2b has activity in advanced CSCC but with considerable toxicity at studied doses. The small sample size precludes meaningful conclusions on efficacy, though the CR observed post-PD1 progression might warrant further investigation of this combination as a therapeutic strategy given the recent approval of cemiplimab in CSCC. Clinical trial information: NCT02218164.

Association between human papillomavirus (HPV) status and duration of response of anti-programmed cell death protein-1 (PD-1) inhibitors in patients with recurrent/metastatic (R/M) head and neck squamous cell carcinoma (HNSCC)

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Background: Human papillomavirus status is known to be prognostic for patients with HNSCC. Current data suggests that HPV-positive HNSCC tumors exhibit increased infiltration of immune cells and higher levels of T-cell exhaustion markers compared with HPV-negative tumors, possibly suggesting a difference in response patterns to immunotherapy. We evaluated whether HPV status is associated with duration of response in patients receiving anti-PD-1 inhibitors. Methods: We performed a retrospective chart review of 54 patients at Moffitt Cancer Center who received either pembrolizumab (N = 32) or nivolumab (N = 22) from February 2016 to July 2018 for R/M HNSCC. We collected the following data for our patient population: primary site of disease, stage, smoking status, duration of treatment, and overall survival (OS). Overall survival time was defined as the date of starting anti-PD-1 inhibitors to death. Primary disease site was oropharynx (N = 25), oral cavity (N = 13), larynx (N = 11), nasopharynx (N = 3) and unknown primary (N = 2). HPV status was available for 37 patients. Analysis of survival and time on treatment was done using log-rank test. Results: Overall survival was not different with respect to primary site of disease, smoking, ECOG status, or type of anti-PD-1 inhibitor, but was significantly longer for patients with HPV-positive vs HPV-negative HNSCCs (17 months vs 4.5 months; log rank p < 0.001). Time on anti-PD-1 inhibitor was also significantly longer for patients with HPV-positive HNSCCs (7 months vs 3 months; log rank p < 0.001). Conclusions: Our data suggests patients with HPV-positive R/M HNSCCs have longer duration of response and OS on anti-PD-1 inhibitors compared to HPV-negative patients.

An Analysis of the Sensitivity of Proteogenomic Mapping of Somatic Mutations and Novel Splicing Events in Cancer

Improvements in mass spectrometry (MS)-based peptide sequencing provide a new opportunity to determine whether polymorphisms, mutations, and splice variants identified in cancer cells are translated. Herein, we apply a proteogenomic data integration tool (QUILTS) to illustrate protein variant discovery using whole genome, whole transcriptome, and global proteome datasets generated from a pair of luminal and basal-like breast-cancer-patient-derived xenografts (PDX). The sensitivity of proteogenomic analysis for singe nucleotide variant (SNV) expression and novel splice junction (NSJ) detection was probed using multiple MS/MS sample process replicates defined here as an independent tandem MS experiment using identical sample material. Despite analysis of over 30 sample process replicates, only about 10% of SNVs (somatic and germline) detected by both DNA and RNA sequencing were observed as peptides. An even smaller proportion of peptides corresponding to NSJ observed by RNA sequencing were detected (<0.1%). Peptides mapping to DNA-detected SNVs without a detectable mRNA transcript were also observed, suggesting that transcriptome coverage was incomplete (∼80%). In contrast to germline variants, somatic variants were less likely to be detected at the peptide level in the basal-like tumor than in the luminal tumor, raising the possibility of differential translation or protein degradation effects. In conclusion, this large-scale proteogenomic integration allowed us to determine the degree to which mutations are translated and identify gaps in sequence coverage, thereby benchmarking current technology and progress toward whole cancer proteome and transcriptome analysis.

Association of the 3'-untranslated region KRAS-variant with cisplatin resistance in patients with recurrent and/or metastatic head and neck squamous cell carcinoma

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Background: A germline mutation in let-7 complementary site 6 (LCS6) within the KRAS 3'-untranslated region (rs61764370, the KRAS-variant: TG/GG) is known to associate with poor outcome and drug resistance in various cancers compared to the wild type allele (TT). We examine the prognostic significance of the KRAS-variant in recurrent/metastatic (R/M) head and neck squamous cell carcinoma (HNSCC). Methods: The KRAS-variant was determined in 116 tumor DNA samples from HNSCC patients enrolled in 3 clinical trials and a tissue collection study using a previously validated PCR-based assay. Results: KRAS-variant status could be determined in 108/116 (93%) samples and an allele frequency of TG/GG was 28.7%. These results were correlated with patient demographics, p16/human papillomavirus (HPV) status and clinical outcome. There was no association between p16/HPV status and the KRAS-variant status (Fisher’s exact test, p=1.0). The KRAS-variant was associated with poor progression-free survival in patients treated with cisplatin+/-cetuximab (log-rank p=0.002) but this association was not observed in docetaxel/bortezomib treated patients (log-rank p=0.89). Conclusions: KRAS-variant is a potentially promising biomarker of poor prognosis and a predictive biomarker of cisplatin resistance in R/M HNSCC. Prospective validation is warranted. Clinical trial information: NCT00003809.

Nuclear epidermal growth factor receptor and p16 expression in head and neck squamous cell carcinoma

OBJECTIVES/HYPOTHESIS

Epidermal growth factor receptor (EGFR) and p16 (a surrogate marker of human papillomavirus [HPV] infection) expression are strong prognostic factors in patients with head and neck squamous cell carcinoma (HNSCC).

STUDY DESIGN

We examined expression levels of total and nuclear EGFR as well as p16 status based on evidence that nuclear EGFR may have a role in DNA damage repair.

METHODS

An HPV-negative (SQ20B) and an HPV-positive (UMSCC47) HNSCC cell line were examined for EGFR and γH2AX expression. A tissue microarray containing 123 cores obtained from 101 HNSCC tumors was analyzed for EGFR expression by automated quantitative analysis and p16 expression by immunohistochemical staining, and these results were correlated with available clinical data.

RESULTS

SQ20B had higher EGFR expression than UMSCC47. Nuclear localization of EGFR on activation with transforming growth factor-α was observed in SQ20B, but not in UMSCC47. SQ20B also had increased γH2AX foci compared to UMSCC47, suggesting that SQ20B has more DNA damage compared to UMSCC47. Total and nuclear EGFR was reliably obtained from 80 of 101 patients. p16 levels were determined in 87 of 101 patients. p16 levels were strongly associated with the oropharyngeal subsite and poorly differentiated histology. Expression of total and nuclear EGFR was higher in p16-negative tumors compared to p16-positive tumors (Wilcoxon rank test, P = .038 and P = .014, respectively).

CONCLUSIONS

Further studies are required to determine a mechanistic link between these two prognostic factors and the significance of EGFR localization to nucleus in DNA damage repair pathway activation.

Application of genomic and proteomic technologies in biomarker discovery

Sequencing of the human genome was completed in 2001. Building on the technology and experience of whole-exome sequencing, numerous cancer genomes have been sequenced, including head and neck squamous cell carcinoma (HNSCC) in 2011. Although DNA sequencing data reveals a complex genome with numerous mutations, the biologic interaction and clinical significance of the overall genetic aberrations are largely unknown. Comprehensive analyses of the tumors using genomics and proteomics beyond sequencing data can potentially accelerate the rate and number of biomarker discoveries to improve biology-driven classification of tumors for prognosis and patient selection for a specific therapy. In this review, we will summarize the current genomic and proteomic technologies, general biomarker-discovery paradigms using the technology and published data in HNSCC-including potential clinical applications and limitations.

Abstract 2254: Nuclear and cytoplasmic epidermal growth factor receptor and p16 expression as prognostic biomarkers in head and neck squamous cell carcinoma

Introduction: Epidermal growth factor receptor (EGFR) and p16 staining have demonstrated to be strong prognostic factors in patients with head and neck squamous cell carcinoma (HNSCC). Patients with higher expression of EGFR in their tumors have been correlated with decreased survival and shorter time to recurrence. Patients with p16-positive (+) tumors [a surrogate marker of human papillomavirus (HPV) infection] have improved survival compared to p16-negative (−) tumors. We examined the interaction between the expression levels of total EGFR and p16 status, and further examined the association between nuclear EGFR and p16 status based on evidence that nuclear EGFR may have a distinct role in DNA damage repair and may function as a transcription factor.

Methods: A tissue microarray (TMA) containing 123 cores obtained from 101 HNSCC tumors was analyzed for EGFR expression (clone H11; DAKO, Carpinteria, CA) using an automated quantitative analysis (AQUA), and for p16 expression (clone E6H4; MTM Laboratories Inc., Westbrough, MA) using immunohistochemical (IHC) staining. Duplicate cores from a patient were averaged for analyses. The EGFR and p16 data were correlated with clinical data including demographics, primary subsite, disease stage, and survival.

Results: The total and nuclear EGFR data could be reliably obtained from 80 of 101 patients. The p16 data could be obtained from 87 of 101 patients [p16 (+), n=29; p16 (−), n=58]. The p16 staining was strongly associated with the oropharyngeal subsite (Chi2, p=&lt;0.0001) and poorly differentiated histology (Cochran-Armitage Trend Test, p=0.01). The expression of total and nuclear EGFR was higher in p16 (−) tumors compared to p16 (+) tumors (Wilcoxon Rank Test, p=0.038 and p=0.014, respectively). Interestingly, the higher expression of non-nuclear EGFR (combined cytoplasmic and membranous) staining did not associate significantly with p16 (−) tumors. Statistically significant differences in recurrence-free survival or overall survival were not detectable based on the EGFR and p16 expression, likely due to the small sample size and heterogeneity in the patient population.

Conclusions: The total and nuclear EGFR expression levels were higher in p16 (−) tumors compared to p16 (+); this may relate to recurrence and poor survival. Additionally, localization of EGFR may be a significant factor in its association with clinical outcomes. Further studies are indicated to determine the mechanistic link between these two prognostic factors and define the significance of EGFR localization to nucleus upon activation of the pathway.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2254. doi:10.1158/1538-7445.AM2011-2254

Abstract 2276: Proteomic analysis of chemoresistance in colorectal cancer cells: potential paracrine mechanisms of resistance

Background: Chemoresistance occurs in nearly all patients with metastatic colorectal cancer (CRC), and mechanisms to reverse chemoresistance remain elusive. We tested the hypothesis that CRC cells resistant to 5-fluorouracil (5FU-R) and oxaliplatin (Ox-R) exhibit proteomic profiles that may identify previously unrecognized mediators of resistance. In prior studies, we found that conditioned media from oxaliplatin-resistant HT29 cells (Ox-R) could mediate growth and chemoresistance in chemonaive parental HT29 cells in vitro. We sought to identify soluble factors in conditioned media that are potential mediators of the paracrine cell survival mechanisms.

Methods: Parental HT29 (Par) cells were grown in increasing concentrations of 5-FU and oxaliplatin to generate 5FU-R and Ox-R cells. Protein from cell lysates and conditioned media (CM) were analyzed by liquid chromatography-mass spectrometry (LC-MS), and spectral counts were compared. Antibody-conjugated bead technology and ELISAs were used to obtain cytokine profiles of CM. Reverse phase proteomic arrays (RPMA) were used to determine signal transduction pathways activated in cells treated with CM. Ox-R cells were injected into nude mice to determine the paracrine effect on Par cells growing on the opposite flank.

Results: Chemoresistant cells displayed significantly different proteomic profiles. In 5FU-R cells, pathways involving oxidative phosphorylation, inositol metabolism, actin cytoskeleton signaling, regulation of actin-based motility by Rho, and ATM signaling were significantly altered vs Par cells. In Ox-R cells, pathways mediating pyruvate metabolism, integrin signaling, caveolar-mediated endocytosis signaling, and mitochondrial dysfunction were among the most altered vs Par cells. Comparison of 5FU-R and Ox-R cells revealed differences in RNA post-transcriptional modification, ERK/MAPK, RAN, and chemokine signaling. Cytokine profiling demonstrated a significant increase in stem cell factor/c-Kit ligand (p=0.02) and a decrease in TRAIL (p=0.008) and IL-10 (p=0.04). RPPA analysis demonstrated early phosphorylation of EGFR and MEK1 followed by GSK, and mTOR activation. Ox-R tumors growing in vivo induced faster and larger tumor growth of contralateral Par tumors indicating a systemic effect. Conclusions: Chemoresistant CRC cells exhibit proteomes that reflect specific survival pathways, with many previously unrecognized potential mediators of resistance. Analysis of soluble factors from chemoresistant CRC cells demonstrates the presence of numerous potential mediators of cancer cell survival that may act, not only in an autocrine/paracrine manner, but also systemically.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2276.

Phosphoinositide kinase-3 status associated with presence or absence of human papillomavirus in head and neck squamous cell carcinomas

PURPOSE

To investigate phosphoinositide kinase-3 (PI3K) activation in relation to human papillomavirus (HPV) status in head and neck squamous cell carcinoma (HNSCC).

METHODS AND MATERIALS

Gene expression microarray data were analyzed to determine differentially expressed genes between HPV(+) and HPV(-) HNSCC. PIK3CA gene expression was confirmed by quantitative reverse transcriptase-polymerase chain reaction in seven HPV(+) and seven HPV(-) primary HNSCCs. PIK3CA mutation status in three HPV(+) and nine HPV(-) cell lines was determined by polymerase chain reaction amplification of hot spot exons (1, 9, 20) followed by direct sequencing.

RESULTS

PIK3CA was overexpressed in HPV(+)-associated HNSCC compared with the expression in HPV(-) HNSCC. Activation of PIK3CA by mutation was found in 1 of the 12 tested HNSCC cell lines.

CONCLUSION

Activation of PI3K by mutation of PIK3CA is rare in HNSCC cell lines and was not found in three HPV(+) cell lines. One mechanism by which HPV-associated HNSCC might activate PI3K is increased expression of PIK3CA.

Carcinogen-induced lymphomagenesis in pim-1 transgenic mice: dose dependence and involvement of myc and ras

Transgenic mice overexpressing the pim-1 oncogene in their lymphoid compartments are predisposed to T-cell lymphomagenesis but only to the extent that approximately 10% of the transgenic mice develop lymphomas within 34 weeks after birth. Recently, we have shown that lymphomagenesis in pim-1 transgenic mice can be accelerated by infecting pim-1 transgenic mice with murine leukemia viruses or by treating the mice with a relatively low dose of 60 mg of the carcinogen N-ethyl-N-nitrosourea (ENU) per kg of body weight. Here we describe the incidence of tumors as a function of the dose of ENU. Either 200, 15, 4, 1, or 0.1 mg/kg ENU was injected into transgenic and control mice and the tumor incidence was monitored. T-cell lymphomas developed in 100 and 70% of the pim-1 transgenic mice treated with 200 and 15 mg/kg ENU, respectively. Approximately 20% of the Emu-pim-1 transgenic mice developed lymphomas after treatment with either 4, 1, or 0.1 mg/kg ENU. The nontransgenic mice developed lymphomas only after injection with 200 mg/kg (45%). The data show that Emu-pim-1 transgenic mice are approximately 25-fold more susceptible to ENU-induced lymphomagenesis than control mice. In most tumors the expression of c-myc was strongly elevated, probably as a direct or indirect effect of ENU. Analysis of the lymphomas for ras mutations revealed that approximately 10% of the lymphomas bear a ras mutation. The data indicate that at least some of these mutations are not the direct result of alkylation by ENU but rather represent spontaneous mutations that occurred later in the tumorigenic process.

Very high frequency of lymphoma induction by a chemical carcinogen in pim-1 transgenic mice

Infection of mice with Moloney murine leukaemia virus (MuLV) induces T-cell lymphomas after an average latency period of 150 days. In these lymphomas the MuLV DNA is frequently integrated into the mouse chromosomal DNA in the vicinity of the pim-1 oncogene. Transgenic mice overexpressing the pim-1 oncogene are predisposed to develop T-cell lymphomas, but only to the extent that approximately 10% of the mice develop a lymphoma within 240 days. When these mice are infected with MuLV, lymphomas develop in all mice in only 50-60 days. In these lymphomas MuLV DNA is integrated near either the c-myc or N-myc gene, suggesting that pim-1 and myc synergize in lymphomagenesis. To determine whether this system has a more general application, we have now tested the susceptibility of pim-1 transgenic mice to N-ethyl-N-nitrosourea (ENU), a chemical carcinogen. With a single low dose of ENU, nearly all pim-1 transgenic mice, but only 15% of non-transgenic mice, develop T-cell lymphomas within 200 days. All ENU-induced lymphomas in both pim-1 transgenic and non-transgenic mice express high levels of c-myc messenger RNA, supporting the notion that pim-1 and c-myc synergize in lymphoma induction. We propose that pim-1 transgenic mice could be used to test the oncogenic potential of other chemical compounds.