Multi-Organ Carcinogenicity of 3,3′-Dimethoxybenzidine Dihydrochloride Given in Drinking Water to F344/N Rats

3,3′-Dimethoxybenzidine dihydrochloride (DMOB) was evaluated for chronic toxicity and carcinogenicity because benzidine, a structurally related chemical, is a known human carcinogen, and because of potential human exposure during production of bisazobiphenyl dyes. Previous carcinogenicity studies of DMOB were considered to be inadequate. Toxicology and carcinogenesis studies were conducted by administering 0,80,170, or 330 ppm DMOB (>97.5% purity) in drinking water to groups of F344/N rats for 21 months. Seventy rats of each sex were used in the control group, 45 in the low-dose, 75 in the mid-dose, and 70 in the high-dose group. Ten rats of each sex in the control and 330 ppm dose groups were evaluated after 9 months. After exposure for 9 months, chemical-related neoplastic effects included liver foci, carcinoma of the preputial gland in one male, carcinoma of the clitoral gland in one female, and carcinoma of the Zymbal gland in two male rats. Although designed for 24 months, these studies were terminated at 21 months because significant numbers of exposed rats died with tumors or were sacrificed in moribund condition. Chemical-related nonneoplastic effects were hematopoietic cell proliferation in the spleen, and cystic and centrilobular degeneration and necrosis of the liver. 3,3′-Dimethoxybenzidine was clearly carcinogenic for male and female F344/N rats. After exposure for up to 21 months, significantly increased incidences of neoplasms were observed in multiple sites: skin, Zymbal gland, preputial and clitoral glands, oral cavity, small and large intestines, liver, brain, mesothelium, mammary gland, and uterus of treated rats.

Carcinogenesis Bioassay of Propyl Gallate in F344 Rats and B6C3FJ Mice

Chronic toxicity studies were conducted by maintaining groups of 50 F344 rats and 50 B6C3F1 mice of each sex on nutritionally complete diets containing 0%, 0.6%, or 1.2% propyl gallate for 103 weeks. Survival of rats and mice of both sexes was not significantly affected by the administration of this compound. Dosed rats and mice showed growth retardation and reduced feed utilization efficiency. Increased incidence of hepatic cytoplasmic vacuolization and suppurative inflammation of the prostate gland were observed in dosed male rats and were considered to be related to propyl gallate administration. Tumors of the preputial gland, islet ceil tumors of the pancreas, and pheochromocytoma of the adrenal gland were observed with significantly (p < 0.05) higher incidence in the low-dose male rats; however, there was little evidence of a dose response or of an effect in the high-dose group. Rare tumors (an astrocytoma and a glioma) were found in the brains of two low-dose female rats but none was found in the high-dose group. Malignant lymphoma occurred with a significant (p < 0.05) positive trend in male mice and the incidence in the high-dose group was significantly (p < 0.05) higher than that of the concurrent controls. However, the high-dose incidence was not significantly different from the historical control rate for the laboratory that conducted the bioassay. Under the conditions of the bioassay, propyl gallate was not considered to be clearly carcinogenic for F344 rats, although the increased incidence of preputial gland tumors, islet-cell tumors of the pancreas, and pheochromocytoma of the adrenal glands in low-dose male rats may have been related to compound administration. Thus, the evidence for carcinogenicity in male rats is regarded as being equivocal, while there was no indication of a carcinogenic response in female rats. Propyl gallate was not considered to be carcinogenic for B6C3F1 mice, although the increased incidence of malignant lymphoma in dosed male mice may have been related to administration of the test compound.

Prediction of Rodent Carcinogenesis: An Evaluation of Prechronic Liver Lesions as Forecasters of Liver Tumors in NTP Carcinogenicity Studies

The National Toxicology Program (NTP) developed the chronic 2-year bioassay as a mechanism for predicting the carcinogenic potential of chemicals in humans. The cost and duration of these studies has limited their use to small numbers of selected chemicals. Many different short-term methods aimed at increasing predictive accuracy and the number of chemicals evaluated have been developed in attempts to successfully correlate their results with evidence of carcinogenicity (or lack of carcinogenicity). Using NTP studies, the effectiveness of correlating prechronic liver lesions with liver cancer encompassing multiple studies using mice (83 compounds) and rats (87 compounds) was assessed. These lesions include hepatocellular necrosis, hepatocellular hypertrophy, hepatocellular cytomegaly, bile duct hyperplasia, and hepatocellular degeneration, along with increased liver weight. Our results indicate that pooling 3 of these prechronic data points (hepatocellular necrosis, hepatocellular hypertrophy, and hepatocellular cytomegaly) can be very predictive of carcinogenicity in the 2-year study ( p < 0 .05). The inclusion of increased liver weight as an endpoint in the pool of data points increases the number of rodent liver carcinogens that are successfully predicted ( p < 0 .05), but also results in the prediction of increased numbers of noncarcinogenic chemicals as carcinogens. The use of multiple prechronic study endpoints provides supplementary information that enhances the predictivity of identifying chemicals with carcinogenic potential.

Selecting the appropriate rodent diet for endocrine disruptor research and testing studies

Selecting the optimum diet for endocrine disruptor (ED) research and testing studies in rodents is critical because the diet may determine the sensitivity to detect or properly evaluate an ED compound. Dietary estrogens can profoundly influence many molecular and cellular event actions on estrogen receptors and estrogen-sensitive genes. The source, concentration, relative potency, and significance of dietary estrogens in rodent diets are reviewed, including dietary factors that focus specifically on total metabolizable energy and phytoestrogen content, which potentially affect ED studies in rodents. Research efforts to determine dietary factors in commercially available rodent diets that affect uterotrophic assays and the time of vaginal opening in immature CD-1 mice are summarized. A checklist is provided of important factors to consider when selecting diets for ED research and testing studies in rodents. Specific metabolizable energy levels are recommended for particular bioassays. Discussions include the between-batch variation in content of the phytoestrogens daidzein and genistein, the effects of total metabolizable energy and phytoestrogens on the timing (i.e., acceleration) of vaginal opening, and increased uterine weight in immature CD-1 mice. It is concluded that rodent diets differ significantly in estrogenic activity primarily due to the large variations in phytoestrogen content; therefore animal diets used in all ED studies should ideally be free of endocrine-modulating compounds.

Toxicology and carcinogenesis studies of microencapsulated trans-cinnamaldehyde in rats and mice

trans-Cinnamaldehyde is a widely used natural ingredient that is added to foods and cosmetics as a flavoring and fragrance agent. Male and female F344/N rats and B6C3F(1) mice were exposed to microencapsulated trans-cinnamaldehyde in the feed for three months or two years. All studies included untreated and vehicle control groups. In the three-month studies, rats and mice were given diets containing 4100, 8200, 16,500, or 33,000 ppm trans-cinnamaldehyde. In rats, feed consumption was reduced in all exposed groups. In mice, feed consumption was reduced in the highest dose groups. Body weights of all treated males were less than controls. Body weights were reduced in female rats exposed to 16,500 or 33,000 ppm and female mice exposed to 8200 ppm or greater. All rats survived to the end of the study but some male mice in the highest dose groups died due to inanition from unpalatability of the dosed feed. The incidence of squamous epithelial hyperplasia of the forestomach was significantly increased in rats exposed to 8200 ppm or greater and female mice exposed to 33,000 ppm. In mice, the incidence of olfactory epithelial degeneration of the nasal cavity was significantly increased in males and females exposed to 16,500 ppm and females exposed to 33,000 ppm. In the two-year studies, rats and mice were exposed to 1000, 2100, or 4100 ppm trans-cinnamaldehyde. Body weights were reduced in mice exposed to 2100 ppm and in rats and mice exposed to 4100 ppm. In rats, hippuric acid excretion was dose proportional indicating that absorption, metabolism, and excretion were not saturated. No neoplasms were attributed to trans-cinnamaldehyde in rats or mice. Squamous cell papillomas and carcinomas of the forestomach were observed in male and female mice but the incidences were within the NTP historical control range and were not considered to be related to trans-cinnamaldehyde exposure.

An alternative perspective: a critical evaluation of the Waddell threshold extrapolation model in chemical carcinogenesis

In a recent Perspective article (Toxicologic Pathology 31: 260-262, 2003) Waddell asserts that he has developed a log linear extrapolation model that can demonstrate a threshold and resolve for once and for all the uncertainies associated with low dose cancer risk extrapolation. However, his method essentially forces, rather than demonstrates, a threshold, and has many serious flaws that result in significant under-estimation of low dose risk. It would be a serious mistake for the scientific community to adopt Waddell's log linear extrapolation model for chemical carcinogenesis risk assessment.

Carcinogenicity of inhaled vanadium pentoxide in F344/N rats and B6C3F1 mice

Vanadium pentoxide (V2O5) is a slightly soluble compound found in airborne particle emissions from metallurgical works and oil and coal burning. Because the carcinogenic potential of V2O5 was not known, F344/N rats and B6C3F1 mice (N=50/sex/species) were exposed to V2O5 at concentrations of 0, 0.5 (rats only), 1, 2, or 4 (mice only) mg/m3, by whole-body inhalation for 2 years. The survival and body weights of rats were minimally affected by exposure to V2O5. The survival and body weights of male mice exposed to 4 mg/m3 and body weights of all exposed groups of female mice were lower than the controls. Alveolar/bronchiolar (A/B) neoplasms occurred in male rats exposed to 0.5 and 2 mg/m3 at incidences exceeding the National Toxicology Program (NTP) historical control ranges. A marginal increase in A/B neoplasms was also observed in female rats exposed to 0.5 mg/m3. Increases in chronic inflammation, interstitial fibrosis, and alveolar and bronchiolar hyperplasia/metaplasia and squamous metaplasia were observed in exposed male and female rats. A/B neoplasms were significantly increased in all groups of exposed mice. As with rats, increases in chronic inflammation, interstitial fibrosis, and alveolar and bronchiolar epithelial hyperplasia were observed in mice exposed to V2O5. Thus, V2O5 exposure was a pulmonary carcinogen in male rats and male and female mice. The marginal tumor response in the lungs of female rats could not be attributed conclusively to exposure to V2O5. These responses were noted at and slightly above the OSHA permissible occupational exposure limit of 0.5 mg/m3 (dust) (National Institute for Occupational Safety and Health, NIOSH Pocket Guide to Chemical Hazards, U.S. Department of Health and Human Services, Washington, DC, 1997, p. 328).

Toxicology and carcinogenesis studies of microencapsulated citral in rats and mice

Citral, a widely used natural ingredient, is added to foods and cosmetics as a flavoring and fragrance agent. Male and female F344/N rats and B6C3F1 mice were exposed to microencapsulated citral in the feed for 14 weeks or two years. All studies included untreated and vehicle control groups. In the 14-week studies, rats and mice were given diets containing 3,900, 7,800, 15,600, or 31,300 ppm citral. In rats, food consumption was reduced in the two highest dose groups. In mice an apparent increase in food consumption was observed, but was due to mice scattering the feed. Body weights of all treated animals were less than controls. All rats and four male mice were killed moribund in the high dose groups. In rats, forestomach and kidney lesions were observed. At the higher doses, lesions observed in the bone marrow, testes, and thymus in rats and in the ovary in mice were considered related to inanition and resultant moribundity. In the two-year studies, rats were exposed to 1,000, 2,000, or 4,000 ppm citral. Body weights were reduced in the 4,000 ppm rats. Mice were exposed to 500, 1,000, or 2,000 ppm citral. Body weights in the 1,000 and 2,000 ppm groups were reduced. No neoplasms were attributed to citral in rats or mice. Malignant lymphoma occurred with a positive trend and was significantly greater than controls in female mice in the 2,000 ppm group. However, the incidences were within the NTP historical control range and could not be clearly related to citral administration.

Photocarcinogenesis in the Tg.AC mouse: lomefloxacin and 8-methoxypsoralen

The Tg.AC mouse is a good predictor of carcinogenic potential when the test article is administered by dorsal painting (Tennant et al. (1995) Environ. Health Perspect. 103, 942). We have used lomefloxacin (LOME) and 8-methoxypsoralen (8-MOP) in combination with UVA to determine whether the Tg.AC transgenic mouse also responds to parenterally administered photocarcinogens. Female Tg.AC mice were given LOME (25 mg/kg intraperitoneal in normal saline) followed by UVA (25 J/cm2) 1-2 h later, five times every 2 weeks on a repetitive schedule. Other groups received LOME, UVA or vehicle alone. After 16 weeks, the mean numbers of papillomas/mouse +/- SD (% responding) were: saline, 0.3 +/- 0.5 (33%); UVA + saline, 1.3 +/- 0.6 (100%); LOME, 1.9 +/- 1.6 (86%) and LOME-UVA, 1.5 +/- 1.9 (64%). Only the 100% incidence of tumors in the UVA group and the maximum tumor yields in the LOME and UVA groups are significant (P < 0.05) when compared with the control. In a second study, Tg.AC mice were administered the classical photocarcinogen 8-MOP (8 mg/kg intragastric in corn oil) followed by 2 J/cm2 UVA 1-2 h later, five times every 2 weeks on a repetitive schedule. The second group received 8-MOP, whereas the third was exposed to UVA alone. Papillomas began to appear at 2 weeks in the 8-MOP-UVA group, and after 17 weeks the mean numbers of papillomas/mouse +/- SD (% responding) were: 8-MOP-UVA, 6.9 +/- 8.6 (93%); UVA + corn oil, 1.1 +/- 1.2 (69%) and 8-MOP, 1.1 +/- 1.6 (50%). The maximum tumor yield in the 8-MOP-UVA group was significantly higher (P < 0.01) than that in the other two groups. Our findings suggest that more studies need to be done before the Tg.AC mouse can be used with confidence to identify parenterally administered photocarcinogens.

Structure and control of a cell-cell adhesion complex associated with spermiation in rat seminiferous epithelium

Spermiation, the release of late spermatids from the Sertoli cell, is disrupted by a number of toxicants. Control of the spermiation process, and the proteins that interact to adhere mature spermatids to Sertoli cells, is poorly understood. In these studies we used immunohistochemistry, coimmunoprecipitation/Western blotting, and mass spectrometry to refine an earlier model of sperm adhesion proposed by our laboratory. We have identified specific proteins linked together as part of a multiprotein complex, as well as several additional proteins (cortactin, ERK1/2, and 14-3-3 zeta) that may be functioning in both structural and signal transduction roles. The current and prior data suggest that protein phosphorylation is central to the control of spermiation. We also present and characterize an in vitro tubule culture system that allowed functional testing of the spermiation model by pharmacologic manipulation, and yielded data consistent with the importance of protein phosphorylation in spermiation.

Use of historical control data in carcinogenicity studies in rodents

This paper considers the use of historical control data in the evaluation of tumor incidences from carcinogenicity studies in rodents. Although the most appropriate control group for interpretative purposes is always the concurrent control, there are instances in which the use of historical control information can aid an investigator in the overall evaluation of tumor incidence data. One example is rare tumors; another is a tumor that shows a marginally significant result relative to concurrent controls. However, before historical control data can be used in a formal testing framework, a number of important issues must first be considered. The nomenclature conventions and diagnostic criteria for each study should be identical to insure unambiguous identification of all relevant tumors in the historical control database. Criteria should be established that will aid in determining whether a particular study should be included in the database. This will assure a homogeneous set of studies upon which to base statistical comparisons. Since study-to-study variability in tumor rates may exceed what would be expected by chance alone, these sources of variability should be identified and controlled. Finally, statistical procedures should be employed that adjust for extra-binomial variability. This paper also summarizes tumor incidence data from untreated Fischer 344 rats and B6C3F1 mice in the National Toxicology Program (NTP) historical control database. All studies in the database are of two years duration, and all neoplasms occurring with a frequency of 0.5% or more are reported.

Antiretroviral therapy effects on genetic and morphologic end points in lymphocytes and sperm of men with human immunodeficiency virus infection

Many human immunodeficiency virus (HIV)-infected persons receive prolonged treatment with DNA-reactive antiretroviral drugs. A prospective study was conducted of 26 HIV-infected men who provided samples before treatment and at multiple times after beginning treatment, to investigate effects of antiretrovirals on lymphocyte and sperm chromosomes and semen quality. Several antiretroviral regimens, all including a nucleoside component, were used. Lymphocyte metaphase analysis and sperm fluorescence in situ hybridization were used for cytogenetic studies. Semen analyses included conventional parameters (volume, concentration, viability, motility, and morphology). No significant effects on cytogenetic parameters, semen volume, or sperm concentration were detected. However, there were significant improvements in sperm motility for men with study entry CD4 cell counts >200 cells/mm(3), sperm morphology for men with entry CD4 cell counts < or =200 cells/mm(3), and the percentage of viable sperm in both groups. These findings suggest that nucleoside-containing antiretrovirals administered via recommended protocols do not induce chromosomal changes in lymphocytes or sperm but may produce improvements in semen quality.

A retrospective analysis of background lesions and tissue accountability for male accessory sex organs in Fischer-344 rats

Because the paired lobes (ventral, dorsal, lateral, and anterior) of the rat prostate have not been consistently sampled in many carcinogenicity and toxicity studies, comparison among different investigations has been compromised. The lack of specific site identification for prostatic lesions further lessens the value of incidences reported. We present here the lobe-specific incidences and degree of severity of background prostatic, seminal vesicular, and ampullary glandular lesions in 1768 control Fischer-344 rats from 35 recent National Toxicology Program 2-year carcinogenicity and toxicity studies conducted in 4 laboratories. The dorsal and lateral lobes were combined and considered the dorsolateral lobe where inflammation, epithelial degeneration, mucinous cysts, and edema were observed. Inflammation in the dorsolateral lobes was significantly associated with pituitary gland adenoma whose prolactin was suggested to play an important role in pathogenesis of prostatic inflammation. Epithelial degeneration, epithelial hyperplasia, inflammation, edema, and adenoma were conspicuous in the ventral lobes. Inflammation and edema occurred in the anterior lobes (coagulating glands). Inflammation, dilatation, epithelial hyperplasia, edema, and adenoma were observed in the seminal vesicles. Inflammation was also present in the ampullary glands. We suggest an optimal embedment and trimming method in rat prostate and seminal vesicle to ensure adequate, consistent sampling.

Unique renal tubule changes induced in rats and mice by the peroxisome proliferators 2,4-dichlorophenoxyacetic acid (2,4-D) and WY-14643

Peroxisome proliferators are non-mutagenic carcinogens in the liver of rodents, acting both as initiators and promoters. The National Toxicology Program (NTP) conducted a study of several peroxisome proliferators (PPs), including Wyeth (WY)-14643 as a prototypical PP and 2,4-dichlorophenoxyacetic acid (2,4-D) as a weak PP, in Sprague-Dawley rats. B6C3F1 mice, and Syrian hamsters. In the kidney, an unusual change was observed in the outer stripe of the outer medulla, especially in rats treated with 2,4-D or WY-14643. This change was characterized by foci of tubules that were partially or completely lined by basophilic epithelial cells with decreased cytoplasm and high nuclear density. Changes typical of chronic nephropathy such as interstitial fibrosis or basement membrane thickening were not associated with these foci. Results of immunohistochemical staining for catalase and cytochrome P-450 4A in the kidney indicated increased staining intensity in renal tubular epithelial cells primarily in the region where the affected tubules were observed: however, the altered cells were negative for both immunohistochemical markers. Ultrastructurally, affected cells had long brush borders typical of the P3 tubule segment. The most distinguishing ultrastructural change was a decreased amount of electronlucent cytoplasm that contained few differentiated organelles and, in particular, a prominent reduced volume and number of mitochondria; changes in peroxisomes were not apparent. In addition to the lesion in rats, mice treated with the highest dose of 2,4-D, but not WY-14643, manifested similar renal tubular changes as seen by light microscopy. Neither chemical induced renal tubular lesions in hamsters. Hepatocellular changes characteristic of PPs were present in all 3 species treated with WY-14643, but not 2,4-D. These results indicate that the rat is the species most sensitive to the nephrotoxic effects of PPs and there is a site specificity to this toxicity related to areas of PP-related enzyme induction. Although 2,4-D is considered a weak PP for the liver, it was the most effective at inducing renal lesions, indicating that the toxic potency of various PPs will depend on the target organ.

Effects of water-soluble antioxidant from spinach, NAO, on doxorubicin-induced heart injury

Doxorubicin (DOX) produces clinically restorative responses in numerous human cancers, but its cardiotoxicity has limited its usefulness. Because reactive oxygen species may affect DOX-induced antitumor activity and cardiotoxicity, we evaluated the prophylactic effect of spinach natural antioxidant (NAO) on DOX-induced cardiotoxicity and oxidative stress in female Balb/c mice using histological, electron microscopical and biochemical parameters. Mice were treated with NAO for 7 days prior to and/or for 6 days after DOX administration. Pretreatment with NAO (cumulative dose: 130 mg/kg) did not hinder the effectiveness of DOX. Light and electron microscopy of DOX-treated heart revealed myocardial degeneration. When administered combined before and after DOX, NAO conferred the most significant cardiac protection. The effects of NAO on the lipid peroxidation product, malondialdehyde, and on H2O2/ hydroperoxides were examined on day 6 following DOX administration; levels of both were elevated in DOX-treated mice, compared to control. Pretreatment with NAO prevented these changes. Pretreatment with NAO before DOX administration decreased catalase and increased superoxide dismutase activities compared to the DOX group. Our results suggest usage of NAO in combination with DOX as a prophylactic strategy to protect heart muscle from DOX-induced cellular damage.

Statistical Issues in the Analysis of Low-Dose Endocrine Disruptor Data

The National Institute of Environmental Health Sciences (NIEHS) and the U.S. Environmental Protection Agency (U.S. EPA) recently cosponsored the Endocrine Disruptors Low-Dose Peer

REVIEW

The purpose of this meeting was to examine data supporting the presence or absence of low-dose effects of endocrine disruptors in specific studies and then to evaluate the likelihood and significance of these and/or other potential low-dose effects for humans. All invited speakers agreed to provide their raw data in advance of the meeting to a Statistics Subpanel, which was asked to reevaluate the authors' experimental design, data analysis, and interpretation of experimental results. The purpose of this statistical reevaluation was to provide an independent assessment of the experimental design and data analysis used in each of the studies and to identify key statistical issues relevant to the evaluation and interpretation of the data. This paper presents a summary of the Statistics Subpanel's evaluation. Specific examples are presented to illustrate problems that arose in the experimental design and data analysis of certain studies. The statistical principles and issues that are discussed in this paper are not unique to endocrine disruptor studies and should provide important guidelines regarding appropriate experimental design and statistical analysis for other types of laboratory investigations.

Effects of the dietary phytoestrogens daidzein and genistein on the incidence of vulvar carcinomas in 129/J mice

The objective of this study was to determine the effect of dietary phytoestrogens on the incidence of spontaneous vulvar carcinomas in 129/J mice using three natural ingredient diets and two purified diets containing predetermined levels of daidzein and genistein. Eighty weanling female mice without clinical evidence of vulvar carcinomas were randomly assigned 16 per diet to each of 5 test diets. Mice were clinically examined for vulvar masses weekly for 3 months and at monthly intervals thereafter. Vulvar carcinomas in representative groups of mice were confirmed using routine histological procedures. The incidence of vulvar carcinomas increased sharply in mice on all test diets during the first 2 months with minor changes during the remainder of the study. Within one month, the incidence of vulvar carcinomas in mice fed the AIN-76A modified soy protein diet was significantly (P < .05) increased over those of mice fed the AIN-76A modified casein diet, the #5K96, or the # 5058 diet. At three months, the incidence of vulvar carcinomas in mice fed the soy protein diet was significantly (P < .05) increased over those of mice fed the NIH-31 diet or the PMI #5K96 diet. There was a marginally significant (P < .10) correlation between the total daidzein and genistein levels in the five test diets and the incidence of vulvar carcinomas in mice as determined by clinical examination. We concluded that dietary levels of daidzein and genistein were associated with an increase in the incidence of vulvar carcinomas in mice and that the 129/J mouse may provide an animal model for studying the development of vulvar carcinomas.

Immunohistochemical localization of growth factors and their receptors in uterine leiomyomas and matched myometrium

Immunolocalization of transforming growth factor alpha (TGF-Alpha), epidermal growth factor (EGF), insulinlike growth factor (IGF)-I, vascular endothelial growth factor (VEGF(165,189,121)), basic fibroblast growth factor (FGF)-2, EGF receptor (R), IGF-IRbeta, and FGFR-1 was studied in uterine leiomyomas and matched myometrial samples taken from seven women (42-47 years of age) in the proliferative phase of the menstrual cycle. Immunolocalization of growth factor peptides was accomplished with either monoclonal or polyclonal antibodies to the amino or carboxy terminus of growth factor peptides or their respective receptors, or against full-length recombinant growth factor. All reactions were conducted using the avidin-biotin complex method. Immunolocalization of TGF-alpha, EGF, EGF-R, IGF-I, IGF-IRbeta, FGF-2, FGFR-1, and VEGF was observed in the cytoplasm of smooth-muscle cells of leiomyomas and matched myometrium. The cytoplasm of vascular smooth-muscle cells expressed TGF-alpha, EGF, EGF-R, IGF-I, IGF-IRbeta, FGF-2, FGFR-1, and VEGF, whereas the vascular endothelium was positive for TGF-alpha, EGF, EGF-R, FGF-2, and FGFR-1 in both leiomyomas and matched myometria. Fibroblasts within the fibrous component of some leiomyomas were positive for IGF-I and FGF-2 and minimally positive for FGFR-1. In addition, the extracellular matrix of leiomyomas showed focal localization of FGF-2 and IGF-I in some tumors. When scores of intensity and percent positive staining were compared, IGF-IRbeta was significantly increased in the leiomyomas compared to matched myometria, whereas EGF was significantly decreased in the uterine leiomyomas compared to matched myometria. In summary, these data revealed growth factors to be expressed differentially in smooth muscle, vascular and fibroblastic cell types of leiomyomas and matched myometria. Specifically, IGF-IRbeta was significantly increased in leiomyomas; although a similar increase was seen with IGF-I peptide, statistical significance was not achieved. The EGF peptide was significantly decreased in the leiomyomas compared to matched myometrium. These data suggest that IGF-IRbeta and IGF-I peptide may be one of several growth factor/receptor pathways important in uterine leiomyoma growth during the proliferative phase of the menstrual cycle. In addition, decreased EGF may be secondary to the predominant estrogenic milieu present at time of sampling, as it has been proposed that progesterone, and not estrogen, may regulate EGF.