RESUMEN
Identifying cellular drivers responsible for enhancing cancer cell resistance to therapeutics provides critical information for designing more effective drugs. Populations of slowly growing, self-renewing, chemo-resistant cells purportedly contribute to the development of therapeutic resistance in many solid tumors. In the current study, we implemented a tumor spheroid model to determine whether NAD(P)H quinone oxidoreductase-1 (NQO1) was requisite for self-renewal and promotion of the drug-resistant phenotype in non-small cell lung cancer (NSCLC). We found that stable depletion of NQO1 in A549 and H358 human NSCLC tumor models inhibits self-renewal capabilities, as demonstrated by a reduced ability to form primary, secondary, and tertiary spheroids. In contrast, the rescue of NQO1 expression restored the tumor cells' ability to form spheroids. Additionally, we discovered that NQO1 depletion renders cisplatin-refractory tumor spheroids highly susceptible to drug treatment. Together, these results suggest that NQO1 loss reduces the self-renewing capabilities of NSCLC cells and enhances their susceptibility to clinically relevant therapeutics. These findings describe a novel role for NQO1 and suggest that combining NQO1-inhibitors with conventional chemotherapeutics may enhance anti-tumor effects.
Asunto(s)
Carcinoma de Pulmón de Células no Pequeñas , Resistencia a Antineoplásicos , Neoplasias Pulmonares , NAD(P)H Deshidrogenasa (Quinona) , Humanos , Carcinoma de Pulmón de Células no Pequeñas/tratamiento farmacológico , Carcinoma de Pulmón de Células no Pequeñas/genética , Carcinoma de Pulmón de Células no Pequeñas/patología , Resistencia a Antineoplásicos/genética , Neoplasias Pulmonares/tratamiento farmacológico , Neoplasias Pulmonares/genética , Neoplasias Pulmonares/metabolismo , NAD , NAD(P)H Deshidrogenasa (Quinona)/genética , NAD(P)H Deshidrogenasa (Quinona)/metabolismo , NADH NADPH Oxidorreductasas , Quinonas , Células A549/efectos de los fármacos , Células A549/metabolismoRESUMEN
BACKGROUND: New approaches to ovarian cancer are needed to improve survival. Wilms' tumour 1 (WT1) is a tumour-associated antigen expressed in many ovarian cancers. P53 is also often altered. The clinical significance of the combined expression of these two transcription factors has not been studied. METHODS: One hundred ninety-six ovarian tumours were classified histopathologically. Tumours were stained for WT1 and p53 immunohistochemically. Stains were analysed according to tumour type, grade and FIGO stage. Kaplan-Meier analyses on 96 invasive carcinomas determined whether categorical variables were related to survival. RESULTS: WT1 and p53 were related to ovarian tumour type, grade, FIGO stage and patient survival. Uniform nuclear p53 expression was associated with invasion and WT1 expression was associated with advanced grade, FIGO stage and poor survival. When WT1 and p53 were both in the age-adjusted Cox model, WT1 was significant while p53 was not. When we combined tumours expressing WT1 and p53, then adjusted for age and tumour subtype, the hazard ratio compared to tumours without WT1 and with normal p53 was 2.70; when adjusted for age and FIGO stage, the hazard ratio was 2.40. CONCLUSIONS: WT1, an antigen target, is a biomarker for poor prognosis, particularly when combined with altered p53.
Asunto(s)
Biomarcadores de Tumor/metabolismo , Núcleo Celular/metabolismo , Neoplasias Ováricas/patología , Proteína p53 Supresora de Tumor/metabolismo , Regulación hacia Arriba , Proteínas WT1/metabolismo , Factores de Edad , Anciano , Femenino , Regulación Neoplásica de la Expresión Génica , Humanos , Estimación de Kaplan-Meier , Persona de Mediana Edad , Clasificación del Tumor , Invasividad Neoplásica , Estadificación de Neoplasias , Neoplasias Ováricas/metabolismo , Pronóstico , Estudios RetrospectivosRESUMEN
Early-life environmental factors can influence later-life susceptibility to cancer. Recent evidence suggests that metabolic pathways may mediate this type of latency effect. Previously, we reported that short-term exposure to dichloroacetic acid (DCA) increased liver cancer in mice 84 weeks after exposure was stopped. Here, we evaluated time course dynamics for key events related to this effect. This study followed a stop-exposure design in which 28-day-old male B6C3F1 mice were given the following treatments in drinking water for up to 93 weeks: deionized water (dH2O, control); 3.5 g/l DCA continuously; or 3.5 g/l DCA for 4-52 weeks followed by dH2O. Effects were evaluated at eight interim time points. A short-term biomarker study was used to evaluate DCA effects at 6, 15, and 30 days. Liver tumor incidence was higher in all DCA treatment groups, including carcinomas in 82% of mice previously treated with DCA for only 4 weeks. Direct effects of DCA in the short-term study included decreased liver cell proliferation and marked mRNA changes related to mitochondrial dysfunction and altered cell metabolism. However, all observed short-term effects of DCA were ultimately reversible, and prior DCA treatment did not affect liver cell proliferation, apoptosis, necrosis, or DNA sequence variants with age. Key intermediate events resulting from transient DCA exposure do not fit classical cytotoxic, mitogenic, or genotoxic modes of action for carcinogenesis, suggesting a distinct mechanism associated with early-life metabolic disruption.
Asunto(s)
Carcinógenos/toxicidad , Ácido Dicloroacético/toxicidad , Neoplasias Hepáticas Experimentales/inducido químicamente , Animales , Neoplasias Hepáticas Experimentales/patología , Masculino , Ratones , Ratones Endogámicos , Tamaño de los Órganos/efectos de los fármacosRESUMEN
Treatment of metastatic gastric cancer typically involves chemotherapy and monoclonal antibodies targeting HER2 (ERBB2) and VEGFR2 (KDR). However, reliable methods to identify patients who would benefit most from a combination of treatment modalities targeting the tumor stroma, including new immunotherapy approaches, are still lacking. Therefore, we integrated a mouse model of stromal activation and gastric cancer genomic information to identify gene expression signatures that may inform treatment strategies. We generated a mouse model in which VEGF-A is expressed via adenovirus, enabling a stromal response marked by immune infiltration and angiogenesis at the injection site, and identified distinct stromal gene expression signatures. With these data, we designed multiplexed IHC assays that were applied to human primary gastric tumors and classified each tumor to a dominant stromal phenotype representative of the vascular and immune diversity found in gastric cancer. We also refined the stromal gene signatures and explored their relation to the dominant patient phenotypes identified by recent large-scale studies of gastric cancer genomics (The Cancer Genome Atlas and Asian Cancer Research Group), revealing four distinct stromal phenotypes. Collectively, these findings suggest that a genomics-based systems approach focused on the tumor stroma can be used to discover putative predictive biomarkers of treatment response, especially to antiangiogenesis agents and immunotherapy, thus offering an opportunity to improve patient stratification. Cancer Res; 76(9); 2573-86. ©2016 AACR.
Asunto(s)
Neoplasias Gástricas/clasificación , Neoplasias Gástricas/genética , Transcriptoma/genética , Microambiente Tumoral/genética , Animales , Biomarcadores de Tumor/análisis , Biomarcadores de Tumor/genética , Biología Computacional/métodos , Modelos Animales de Enfermedad , Perfilación de la Expresión Génica/métodos , Xenoinjertos , Humanos , Procesamiento de Imagen Asistido por Computador , Inmunohistoquímica , Ratones , Neovascularización Patológica/genética , Análisis de Secuencia por Matrices de Oligonucleótidos , Análisis de Matrices Tisulares , Factor A de Crecimiento Endotelial Vascular/metabolismoRESUMEN
BACKGROUND: Melanoma is a disease that primarily arises in the skin but is a derivative of the neural crest. Eukaryotic translation initiation factor 4E (eIF4E) regulates translation of multiple malignancy-associated mRNAs and is overexpressed in many epithelial tumours. However, expression in human tumours derived from the neural crest is unknown. Here, we determined the association of eIF4E and phospho-eIF4E expression in melanocytic lesions with malignant conversion, metastatic potential and patient survival. METHODS: Archived formalin-fixed, paraffin-embedded surgical specimens from 114 patients with melanocytic lesions were stained immunohistochemically for eIF4E and phospho-eIF4E and evaluated semiquantitatively. The relationship between cytoplasmic and nuclear eIF4E and phospho-eIF4E protein expression, melanocytic lesion subtype and tumour progression was determined. Kaplan-Meier survival analyses and Cox proportional hazard regression were performed. RESULTS: Increased eIF4E and phospho-eIF4E expression was highly associated with malignancy (P<0.0001). High nuclear phospho-eIF4E was associated with synchronous or future metastasis (P=0.0059). Kaplan-Meier analyses demonstrated highly significant associations between high histoscores for cytoplasmic and nuclear phospho-eIF4E and reduced survival in all patients (P=0.0003 and 0.0009, respectively). CONCLUSIONS: Increased melanoma expression of eIF4E and phospho-eIF4E is associated with metastatic potential, reduced survival and increased risk of death.
Asunto(s)
Biomarcadores de Tumor/metabolismo , Factor 4E Eucariótico de Iniciación/metabolismo , Melanoma/metabolismo , Serina/metabolismo , Adulto , Progresión de la Enfermedad , Femenino , Humanos , Inmunohistoquímica , Estimación de Kaplan-Meier , Masculino , Melanoma/mortalidad , Melanoma/patología , Fosforilación , Estudios RetrospectivosRESUMEN
More efficient models are needed to assess potential carcinogenicity hazard of environmental chemicals based on early events in tumorigenesis. Here, we investigated time course profiles for key events in an established cancer mode of action. Using a case study approach, we evaluated two reference phthalates, di(2-ethylhexyl) phthalate (DEHP) and its stereoisomer di-n-octyl phthalate (DNOP), across the span of a two-year carcinogenicity bioassay. Male B6C3F1 mice received diets with no phthalate added (control), DEHP at 0.12, 0.60, or 1.20%, or DNOP at 0.10, 0.50, or 1.00% (n = 80-83/group) for up to 104 weeks with six interim evaluations starting at week 4. Mean phthalate doses were 139, 845, and 3147 mg/kg/day for DEHP and 113, 755, and 1281 mg/kg/day for DNOP groups, respectively. Incidence and number of hepatocellular tumors (adenoma and/or carcinoma) were greater at ≥ 60 weeks for all DEHP groups with time and dose trends, whereas DNOP had no significant effects. Key events supported a peroxisome proliferator-activated receptor alpha (PPARα) mode of action for DEHP, with secondary cytotoxicity at the high dose, whereas DNOP induced modest increases in PPARα activity without proliferative or cytotoxic effects. Threshold estimates for later tumorigenic effects were identified at week 4 for relative liver weight (+24%) and PPARα activity (+79%) relative to the control group. Benchmark doses (BMDs) for these measures at week 4 clearly distinguished DEHP and DNOP and showed strong concordance with values at later time points and tumorigenic BMDs. Other target sites included testis and kidney, which showed degenerative changes at higher doses of DEHP but not DNOP. Our results highlight marked differences in the chronic toxicity profiles of structurally similar phthalates and demonstrate quantitative relationships between early bioindicators and later tumor outcomes.
Asunto(s)
Ácidos Ftálicos/toxicidad , Animales , Carcinogénesis , Relación Dosis-Respuesta a Droga , Hígado/efectos de los fármacos , Hígado/metabolismo , Neoplasias Hepáticas Experimentales/inducido químicamente , Neoplasias Hepáticas Experimentales/metabolismo , Masculino , Ratones , PPAR alfa/metabolismo , Ácidos Ftálicos/administración & dosificación , Ácidos Ftálicos/química , EstereoisomerismoRESUMEN
Elevated eukaryotic translation initiation factor 4E (eIF4E) function induces malignancy in experimental models by selectively enhancing translation of key malignancy-related mRNAs (c-myc and BCL-2). eIF4E activation may reflect increased eIF4E expression or phosphorylation of its inhibitory binding proteins (4E-BP). By immunohistochemical analyses of 148 tissues from 89 prostate cancer patients, we now show that both eIF4E expression and 4E-BP1 phosphorylation (p4E-BP1) are increased significantly, particularly in advanced prostate cancer versus benign prostatic hyperplasia tissues. Further, increased eIF4E and p4E-BP1 levels are significantly related to reduced patient survival, whereas uniform 4E-BP1 expression is significantly related to better patient survival. Both immunohistochemistry and Western blotting reveal that elevated eIF4E and p4E-BP1 are evident in the same prostate cancer tissues. In two distinct prostate cancer cell models, the progression to androgen independence also involves increased eIF4E activation. In these prostate cancer cells, reducing eIF4E expression with an eIF4E-specific antisense oligonucleotide currently in phase I clinical trials robustly induces apoptosis, regardless of cell cycle phase, and reduces expression of the eIF4E-regulated proteins BCL-2 and c-myc. Collectively, these data implicate eIF4E activation in prostate cancer and suggest that targeting eIF4E may be attractive for prostate cancer therapy.
Asunto(s)
Factor 4E Eucariótico de Iniciación/biosíntesis , Neoplasias de la Próstata/metabolismo , Proteínas Adaptadoras Transductoras de Señales/metabolismo , Apoptosis/fisiología , Ciclo Celular/fisiología , Proteínas de Ciclo Celular , Línea Celular Tumoral , Progresión de la Enfermedad , Factor 4E Eucariótico de Iniciación/genética , Humanos , Inmunohistoquímica , Masculino , Oligonucleótidos Antisentido/genética , Fosfoproteínas/metabolismo , Fosforilación , Neoplasias de la Próstata/patología , Proteínas Proto-Oncogénicas c-bcl-2/biosíntesis , Proteínas Proto-Oncogénicas c-bcl-2/metabolismo , Proteínas Proto-Oncogénicas c-myc/metabolismoRESUMEN
The eukaryotic translation initiation factor 4E (eIF4E) is frequently overexpressed in human cancers in relation to disease progression and drives cellular transformation, tumorigenesis, and metastatic progression in experimental models. Enhanced eIF4E function results from eIF4E overexpression and/or activation of the ras and phosphatidylinositol 3-kinase/AKT pathways and selectively increases the translation of key mRNAs involved in tumor growth, angiogenesis, and cell survival. Consequently, by simultaneously and selectively reducing the expression of numerous potent growth and survival factors critical for malignancy, targeting eIF4E for inhibition may provide an attractive therapy for many different tumor types. Recent work has now shown the plausibility of therapeutically targeting eIF4E and has resulted in the advance of the first eIF4E-specific therapy to clinical trials. These studies illustrate the increased susceptibility of tumor tissues to eIF4E inhibition and support the notion that the enhanced eIF4E function common to many tumor types may represent an Achilles' heel for cancer.
Asunto(s)
Factor 4E Eucariótico de Iniciación/antagonistas & inhibidores , Neoplasias/terapia , Animales , Factor 4E Eucariótico de Iniciación/biosíntesis , Factor 4E Eucariótico de Iniciación/genética , Humanos , Neoplasias/genética , Neoplasias/metabolismo , ARN Mensajero/biosíntesis , ARN Mensajero/genéticaRESUMEN
Expression of eukaryotic translation initiation factor 4E (eIF4E) is commonly elevated in human and experimental cancers, promoting angiogenesis and tumor growth. Elevated eIF4E levels selectively increase translation of growth factors important in malignancy (e.g., VEGF, cyclin D1) and is thereby an attractive anticancer therapeutic target. Yet to date, no eIF4E-specific therapy has been developed. Herein we report development of eIF4E-specific antisense oligonucleotides (ASOs) designed to have the necessary tissue stability and nuclease resistance required for systemic anticancer therapy. In mammalian cultured cells, these ASOs specifically targeted the eIF4E mRNA for destruction, repressing expression of eIF4E-regulated proteins (e.g., VEGF, cyclin D1, survivin, c-myc, Bcl-2), inducing apoptosis, and preventing endothelial cells from forming vessel-like structures. Most importantly, intravenous ASO administration selectively and significantly reduced eIF4E expression in human tumor xenografts, significantly suppressing tumor growth. Because these ASOs also target murine eIF4E, we assessed the impact of eIF4E reduction in normal tissues. Despite reducing eIF4E levels by 80% in mouse liver, eIF4E-specific ASO administration did not affect body weight, organ weight, or liver transaminase levels, thereby providing the first in vivo evidence that cancers may be more susceptible to eIF4E inhibition than normal tissues. These data have prompted eIF4E-specific ASO clinical trials for the treatment of human cancers.
Asunto(s)
Factor 4E Eucariótico de Iniciación/metabolismo , Regulación Neoplásica de la Expresión Génica , Neoplasias/metabolismo , Neoplasias/terapia , Biosíntesis de Proteínas/genética , Animales , Apoptosis , Secuencia de Bases , Células Cultivadas , Células Endoteliales/metabolismo , Factor 4E Eucariótico de Iniciación/genética , Humanos , Ratones , Neoplasias/irrigación sanguínea , Neoplasias/patología , Ensayos Antitumor por Modelo de XenoinjertoRESUMEN
PURPOSE: The transforming growth factor-beta (TGF-beta) signaling pathway has been frequently implicated in breast cancer. An intronic variant (Int7G24A) of TGF-beta receptor type I (TGFBR1) is associated with kidney and bladder cancers in our recent study. We hypothesize that this germline variant may be involved in development and progression of breast cancer. EXPERIMENTAL DESIGN: Case-control studies were designed from archived paraffin-embedded tissue specimens from the same geographic area with a homogenous ethnic population. We analyzed 223 patients (25 with preinvasive tumors and 198 with invasive and metastatic breast cancers) and 153 noncancer controls. The Int7G24A was identified by PCR-RFLP. Another germline deletion (TGFBR1*6A) and somatic mutations in the TGFBR1 were also analyzed by PCR and single-strand conformational polymorphism. RESULTS: The Int7G24A allele was evident in 32% of patients with preinvasive neoplasms and 48% of patients with invasive breast cancers compared with 26% controls (P = 0.00008). In addition, 11 (5.6%) homozygous Int7G24A carriers were found in patients with invasive breast cancers, whereas only 3 (2%) homozygous carriers were found in the control group. The TGFBR1*6A allele was not significantly associated with breast cancer patients and only one somatic mutation was found in 71 breast cancers. CONCLUSION: These data suggest that the germline Int7G24A variant may represent a risk factor for invasive breast cancer and a marker for breast cancer progression. A separate study with a larger sample size is warranted to validate the association of the Int7G24A with human breast cancer.
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Receptores de Activinas Tipo I/genética , Neoplasias de la Mama/genética , Variación Genética , Intrones/genética , Invasividad Neoplásica/genética , Receptores de Factores de Crecimiento Transformadores beta/genética , Adulto , Anciano , Anciano de 80 o más Años , Neoplasias de la Mama/metabolismo , Neoplasias de la Mama/patología , Carcinoma Ductal de Mama/genética , Carcinoma Ductal de Mama/metabolismo , Carcinoma Ductal de Mama/secundario , Carcinoma Lobular/genética , Carcinoma Lobular/metabolismo , Carcinoma Lobular/secundario , Estudios de Casos y Controles , Progresión de la Enfermedad , Femenino , Mutación de Línea Germinal/genética , Humanos , Masculino , Persona de Mediana Edad , Invasividad Neoplásica/patología , Reacción en Cadena de la Polimerasa , Polimorfismo de Longitud del Fragmento de Restricción , Polimorfismo Conformacional Retorcido-Simple , Proteínas Serina-Treonina Quinasas , Receptor Tipo I de Factor de Crecimiento Transformador beta , Factores de Riesgo , Eliminación de Secuencia/genéticaRESUMEN
TGF-beta signaling is frequently perturbed in many human cancers, including renal cell carcinomas (RCCs) and transitional cell carcinomas (TCCs) of the bladder. Genetic alterations of the TGF-beta type 1 receptor (TGFBR1) may contribute to these perturbations. We therefore examined variations in the TGFBR1 gene by PCR, SSCP and RFLP in carcinomas of the urinary system and in tissues from noncancer, age-matched controls. A G-->A variant 24 bp downstream of the exon/intron 7 boundary of the TGFBR1 gene (Int7G24A) was evident in patients with RCC (46.5%, n = 86) and bladder and upper urinary tract TCC (49.2%, n = 65) significantly more frequently than in age-matched controls (28.3%, n = 113, p < 0.002 by chi2 test). Moreover, 8 homozygous variant carriers were found in the cancer groups, whereas not a single homozygous variant carrier was found in the control group. The Int7G24A allele (both heterozygous G/A and homozygous A/A carriers) was associated with increased RCC incidence (OR = 2.20, 95% CI 1.22-3.96) and TCC incidence (OR = 2.45, 95% CI 1.89-3.16). One somatic mutation of serine to phenylalanine at codon 57 of the TGFBR1 gene was confirmed in an upper urinary tract TCC. In conclusion, the Int7G24A variant in the TGFBR1 gene is significantly more frequent in patients with RCC and TCC than normal age-matched controls, suggesting that it may represent a risk factor for the development of kidney and bladder carcinomas.
Asunto(s)
Receptores de Activinas Tipo I/genética , Carcinoma de Células Renales/genética , Carcinoma de Células Transicionales/genética , Variación Genética , Intrones/genética , Neoplasias Renales/genética , Receptores de Factores de Crecimiento Transformadores beta/genética , Neoplasias de la Vejiga Urinaria/genética , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Estudios de Casos y Controles , Femenino , Homocigoto , Humanos , Riñón , Masculino , Persona de Mediana Edad , Mutación/genética , Reacción en Cadena de la Polimerasa , Polimorfismo de Longitud del Fragmento de Restricción , Polimorfismo Conformacional Retorcido-Simple , Proteínas Serina-Treonina Quinasas , Receptor Tipo I de Factor de Crecimiento Transformador beta , Vejiga UrinariaRESUMEN
PURPOSE: The p21-activated kinase-1 (Pak-1) promotes cell motility and invasiveness. Pak-1 is activated by the Rac, Rho, and Cdc42 small GTPases in response to a variety of stimuli including ras and phosphatidylinositol 3'-kinase/AKT pathway activation. Because Pak-1 plays a central role in regulating cell motility and invasiveness, we sought to determine whether Pak-1 may be involved in the malignant progression of colorectal carcinoma. EXPERIMENTAL DESIGN: Pak-1 expression was examined by immunohistochemistry in archived tissues from normal human colons, tubular and tubulovillous adenomas, invasive adenocarcinomas (stages I-III/IV), and lymph node metastases (184 total specimens from 38 patients). Specific cytoplasmic immunostaining was evaluated for overall intensity and uniformity to derive a combined histoscore (stain intensity x percentage of epithelium stained). RESULTS: Pak-1 expression was increased significantly with colorectal cancer progression from normal tissue to lymph node metastases (P < 0.0001). Furthermore, Pak-1 expression was increased significantly in adenomas, invasive carcinomas, and lymph node metastases compared with normal colon (P < 0.0001). Strikingly, Pak-1 expression was significantly higher in lymph node metastases than in invasive cancers, adenomas, or normal colon (P < 0.0001). Moreover, in patients with multiple lesions representing different stages of disease, Pak-1 expression was increased specifically in the most advanced lesions. CONCLUSIONS: This study demonstrates that Pak-1 expression is increased significantly with malignant progression of human colorectal carcinoma. These data, along with numerous functional studies demonstrating a central role for Pak-1 activity in tumor invasiveness and motility, implicate Pak-1 as an exciting target for therapy of colorectal carcinoma.
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Neoplasias Colorrectales/patología , Proteínas Serina-Treonina Quinasas/biosíntesis , Adenoma/metabolismo , Carcinoma/metabolismo , Colon/patología , Neoplasias del Colon/patología , Neoplasias Colorrectales/metabolismo , Citoplasma/metabolismo , Progresión de la Enfermedad , GTP Fosfohidrolasas/metabolismo , Humanos , Inmunohistoquímica , Metástasis Linfática , Metástasis de la Neoplasia , Fosfatidilinositol 3-Quinasas/metabolismo , Proteínas Serina-Treonina Quinasas/metabolismo , Resultado del Tratamiento , Proteína de Unión al GTP cdc42/metabolismo , Quinasas p21 Activadas , Proteínas ras/metabolismoRESUMEN
Dichloroacetic acid (DCA) is carcinogenic to the B6C3F(1) mouse and the F344 rat. Given the carcinogenic potential of DCA in rodent liver and the known concentrations of this compound in drinking water, reliable biologically based models to reduce the uncertainty of risk assessment for human exposure to DCA are needed. Development of such models requires identification and quantification of premalignant hepatic lesions, identification of the doses at which these lesions occur, and determination of the likelihood that these lesions will progress to cancer. In this study we determined the dose response of histopathologic changes occurring in the livers of mice exposed to DCA (0.05-3.5 g/L) for 26-100 weeks. Lesions were classified as foci of cellular alteration smaller than one liver lobule (altered hepatic foci; AHF), foci of cellular alteration larger than one liver lobule (large foci of cellular alteration; LFCA), adenomas (ADs), or carcinomas (CAs). Histopathologic analysis of 598 premalignant lesions revealed that (a)) each lesion class had a predominant phenotype; (b)) AHF, LFCA, and AD demonstrated neoplastic progression with time; and (c)) independent of DCA dose and length of exposure effects, some toxic/adaptive changes in non-involved liver were related to this neoplastic progression. A lesion sequence for carcinogenesis in male B6C3F(1) mouse liver has been proposed that will enable development of a biologically based mathematical model for DCA. Because all classes of premalignant lesions and CAs were found at both lower and higher doses, these data are consistent with the conclusion that nongenotoxic mechanisms, such as negative selection, are relevant to DCA carcinogenesis at lower doses where DCA genotoxicity has not been observed.