Abstract  For random effects meta-regression inference, variance estimation for the parameter estimates is discussed. Because estimated weights are used for meta-regression analysis in practice, the assumed or estimated covariance matrix used in meta-regression is not strictly correct, due to possible errors in estimating the weights. Therefore, this note investigates the use of a robust variance estimation approach for obtaining variances of the parameter estimates in random effects meta-regression inference. This method treats the assumed covariance matrix of the effect measure variables as a working covariance matrix. Using an example of meta-analysis data from clinical trials of a vaccine, the robust variance estimation approach is illustrated in comparison with two other methods of variance estimation. A simulation study is presented, comparing the three methods of variance estimation in terms of bias and coverage probability. We find that, despite the seeming suitability of the robust estimator for random effects meta-regression, the improved variance estimator of Knapp and Hartung (2003) yields the best performance among the three estimators, and thus may provide the best protection against errors in the estimated weights.

Abstract  BACKGROUND: Primary thyroid gland lymphomas are uncommon tumours that occur in the setting of lymphocytic thyroiditis or Hashimoto's disease in almost all cases. In this condition a distinction between an inflammatory lymphoid infiltrate and a low grade lymphoma may be extremely difficult and precise criteria are necessary for a correct diagnosis.

PATIENT AND METHODS: We report a case of a minute focus of primary extranodal marginal zone B-cell lymphoma (EMZBCL), incidentally discovered in a 63-year-old man with Hashimoto thyroiditis (HT) and diagnosed by means of polymerase chain reaction (PCR) after laser capture microdissection.The histological examination of surgical specimen confirmed the diagnosis of HT and showed a minute focus of dense lymphoid infiltrate (less than 4 mm in diameter), composed by centrocyte-like cells forming MALT balls. Immunoistochemistry was not useful. A microscopic focus of EMZBCL was suspected on the basis of morphological features. PCR assays revealed the rearrangement of the heavy chain of immunoglobulins only in the microdissected suspicious area, confirming the diagnosis of EMZBCL.

CONCLUSION: Our finding suggests that in cases of autoimmune thyroiditis a careful examination of the thyroid specimen is warranted, in order to disclose areas or small foci of lymphomatous transformation. Furthermore, in difficult cases with doubtful immunohistological findings, ancillary techniques, such as molecular studies, are necessary for a conclusive diagnosis.

Abstract  The results of rat and mouse carcinogenicity studies for 282 human pharmaceuticals in the FDA database were analyzed and compared as part of an International Conference on Harmonization (ICH) evaluation of rodent carcinogenicity studies and their utility for carcinogenicity testing. A majority of the carcinogenicity studies in the FDA database were carried out in Sprague-Dawley-derived rats and Swiss-Webster-derived CD-1 mice in contrast to Fisher 344 rats and B6C3F1 mice employed in National Toxicology Program (NTP) studies. Despite the differences in rodent strains, the relative proportion of compounds with positive findings (44.3%) and the degree of overall concordance between rats and mice (74.1%) in the FDA database were similar to the NTP rodent carcinogenicity database. Carcinogenicity studies in two rodent species are necessary primarily to identify trans-species tumorigens, which are considered to pose a relatively greater potential risk to humans than single species positive compounds. Two-year carcinogenicity studies in both rats and mice may not be the only means of identifying trans-species tumorigens. Sufficient experience is now available for some alternative in vivo carcinogenicity models to support their application as complementary studies in combination with a single 2-year carcinogenicity study to identify trans-species tumorigens. Our analysis of the rodent carcinogenicity studies supports such an approach for assessing carcinogenic potential without compromising the public health.

Abstract  The United States Environmental Protection Agency (EPA) recently proposed a hypothetical mode of action (MOA) to explain how inhaled formaldehyde (FA) might induce leukemia, lymphoma and a variety of other lymphohematopoietic (LHP) malignancies in occupationally exposed workers. The central hypothesis requires that B lymphocytes or hematopoietic progenitor cells (HPC) present at the “portal of entry (POE)” undergo sustained mutagenic change as a result of direct FA exposure. These modified cells would then migrate back to the bone marrow or primary lymphatic tissue and subsequently develop into specific LHP disease states. Chemical interaction at the POE is an absolute requirement for the hypothesized MOA as there is no convincing evidence that inhaled FA causes distant site (e.g., bone marrow) toxicity. The purpose of this review is to critically evaluate this proposed MOA within the context of the existing data concerning the toxicokinetic and biological properties of FA, the current understanding of the induction of chemically-induced leukemias and lymphomas, as well as within EPA’s specific guidelines for evaluating the MOA of chemically-induced cancers. Specifically, we examine the scientific support for the hypothesis that FA exposure may induce carcinogenic transformation of localized lymphocytes or peripheral hematopoietic progenitor cells (HPC) in the absence of discernable systemic hematopoietic toxicity (i.e., peripheral transformation). While little or no empirical evidence exists upon which to fully evaluate the proposed hypothesis, available data does not support the proposed concept of “peripheral transformation” at the chemical entry site. Numerous animal bioassays evaluating chronic inhalation of FA clearly do not support this hypothesis since no properly conducted study as ever shown an increase in any LHP malignancy. Moreover, the notion that FA can cause any LHP malignancy is not supported with either epidemiologic data or current understanding of differing etiologies and risk factors for the various hematopoietic and lymphoproliferative malignancies. It is therefore concluded that existing science does not support the proposed MOA as a logical explanation for proposing that FA is a realistic etiological factor for any LHP malignancy.

Abstract  This publication originates from a workshop held in 1997 to consider how rodent tumours of urinary bladder, renal cortex, and thyroid gland should be treated within the IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. The workshop also addressed the predictive value of these tumours for the identification of carcinogenic hazards to humans when they occur alone and when they occur along with tumours in other organs. In the following sections, etiological risk factors in humans and experimental animals as well as the hypotheses underlying the proposed species-specific mechanisms for each of the above-mentioned tumour types are summarized. Finally, for each tumour type, recommendations are presented on how the mechanistic data could be used in the overall evaluation of carcinogenicity to humans.

Abstract  Vinyl chloride was administered by inhalation, 7 hours daily, 5 days weekly, at concentrations of 2500 and 0 ppm, to Sprague-Dawley rats. The treatment was started on 13-week-old breeders and male and female offspring (12-day embryos). The breeders and part of the offspring were exposed for 104 weeks; the other part of the offspring was exposed for 15 weeks only. Under the experimental conditions, vinyl chloride caused an exceptionally high incidence of brain neuroblastomas, liver angiosarcomas, and hepatocarcinomas. The age at start and/or length of treatment may affect the onset of these tumors in different ways.

Abstract  Vinyl acetate monomer (VAM) was administered in drinking water supplied ad libitum at doses of 5,000, 1,000, and 0 ppm (v/v) to 17-week-old Sprague-Dawley rats (breeders) and to 12-day embryos (offspring). Treatment lasted for 104 weeks; thereafter, animals were kept under control conditions until spontaneous death. VAM was found to cause an increase in total malignant tumors and in carcinomas and/or precursor lesions of the oral cavity, lips, tongue, esophagus, and forestomach. Based on these data, VAM must be considered a multipotent carcinogen.

Abstract  Trichloroethylene was administered by inhalation, 7 hours daily, 5 days weekly, for 8 weeks, at concentrations of 600, 100 and 0 ppm, to Sprague-Dawley rats and Swiss mice; and for 104 weeks to Sprague-Dawley rats; and for 78 weeks to Swiss and B6C3F1 mice at concentrations of 600, 300, 100 and 0 ppm. The animals were kept under observation until spontaneous death. In the experiments reported herein, 3768 animals were studied. Under the experimental conditions, trichloroethylene appears to be carcinogenic in rats and mice (particularly in male Swiss mice). The most relevant finding was the dose-related increased incidence of Leydig cell tumors in male rats, and the onset of few renal tubuli adenocarcinomas at the highest dose, always in rats (4/130 males and 1/130 females). The renal tubuli adenocarcinomas were preceded by, and associated with, a characteristic lesion of the kidney: tubuli cell karyomegaly (megalonucleocytosis).

Abstract  In a continuing review of long-term toxicology and carcinogenesis studies in rats and mice, the National Toxicology Program (NTP) is confronted with many problems concerning the interpretation of tumor data. A frequently raised question is: "Should certain neoplasms be combined for overall assessment of rodent carcinogenesis data?" NTP policy is that certain neoplasms may be combined for statistical assessment of tumor data and that hyperplastic responses may be used as supportive evidence. The primary reason for combining neoplastic lesions is to gain more insight into the evidence of the carcinogenicity of a given chemical in that species of animal. This report gives the rationale, criteria, and guidelines used by the NTP for combining neoplasms for the evaluation of long-term rodent toxicology and carcinogenesis studies. The guidelines are based mainly on lesions occurring in the F344/N inbred rat and (C57BL/6 X C3H)F1 mouse and may or may not be appropriate for other strains or species. The concepts of combining neoplasms and sites should be viewed in terms of the study as a whole, since tumor formation is only one of many responses caused by chemicals in mammals. The resulting information becomes part of the "weight of the evidence" for estimating the potential hazard of a given chemical.

Abstract  Male and female Sprague-Dawley rats of different ages at the start of the experiments (12 day embryos, and 7 and 25 weeks old) were administered fromaldehyde in drinking water at different doses (2,500 or 1,500, 1,000, 500, 100, 50, 10, 0 ppm). An increased incidence of leukemias and of gastro-intestinal tumors was observed in formaldehyde treated rats. Gastro-intestinal tumors are exceptionally rare in the rats of the colony used. These results, together with the ones obtained by other Authors on rats exposed by inhalation to formaldehyde, indicate that this compound is an experimental multipotential carcinogen. The experimental results presented in this report give scientific support to the epidemiological observation of a higher incidence of leukemias and of gastro-intestinal cancers among the people occupationally exposed.

Abstract  Tert-amyl-methyl ether (TAME) was administered by gavage in extra virgin olive oil solution at concentrations of 750, 250, or 0 mg/kg bw to groups of 100 male and 100 female Sprague-Dawley rats 8 weeks old at the start of the experiment. Di-isopropyl ether (DIPE) was administered in the same manner at the doses of 1000, 250, or 0 mg/kg body weight to groups of 100 male and 100 female Sprague-Dawley rats. TAME and DIPE were each delivered in 1-mL solution 4 days a week for 78 weeks. Control animals received 1 mL of extra virgin olive oil without TAME or DIPE. At the end of the treatment period, all animals were kept under observation until spontaneous death. Under these test conditions, TAME and DIPE were found to be potential carcinogenic agents for various organs and tissues.

Abstract  The National Toxicology Program rodent cancer bioassay program design evolved from that of the National Cancer Institute in the 1970s. Groups of 50 or more mice are assigned to control or treatment groups. Test substances are given at three dose levels by intubation, dietary or drinking water consumption, or dermal or inhalation exposure. Dosing starts at age 5-6 weeks and lasts for 2 years, when surviving animals receive a complete histopathologic examination. Statistical approaches accommodate survival differences and no longer require differentiation between fatal and incidental tumors. Photocarcinogenicity studies, employing SKH-1 hairless mice, evaluate onset of skin papillomas and incidences at 1 year. Top doses are chosen to expose animals to a minimally toxic challenge and lower doses to operate within the linear range of kinetics. This dosing allows comparison of results across studies. Bioassay and ancillary studies successfully identify tumor-causing agents in rodents, provide information on dose-response, and characterize other chemical-related toxicities. NTP and Ramazzini Foundation bioassay designs differ in several aspects, but bioassays at both institutions provide chemical-specific information for predicting human carcinogens, thus providing for protection of public health. Bioassays constitute an essential information reference set for new assay development and further investigations into mechanisms of action. The scientific community and the public owe a huge debt of gratitude to Dr. Cesare Maltoni of the European Foundation of Oncology and Environmental Sciences and to Dr. David P. Rall of the National Institute of Environmental Health Sciences for their foresight and wisdom in creating and nurturing these bioassay programs.

Abstract  Lymphomas were reported to be induced in rats in bioassays of aspartame, methyl-tertiary-butyl ether (MTBE), and other chemicals conducted by a nonprofit cancer research organization. European regulatory authorities concluded that lymphomas in the aspartame study were caused by Mycoplasma pulmonis and suggested that this also was the case for the MTBE bioassay. To assess the role of M. pulmonis in these bioassays, we reviewed the tumor data for the aspartame and MTBE bioassays and, additionally, the organization's bioassay of methanol. For all 3 studies, the most frequently reported hematopoietic neoplasm was lympho-immunoblastic lymphoma, the most frequently affected organ was the lung, and, in almost half of the rats with this diagnosis, the lung was the only affected organ. Lesions diagnosed as lymphoma in published illustrations had pleomorphic cellular morphology and appeared to contain neutrophils. Information from these reports and other sources indicated that lesions typical of M. pulmonis disease were prevalent among the aspartame and MTBE study rats and that the rats were not specific-pathogen?free. Because the lymphoma type, cellular morphology, and organ distribution reported in these studies are atypical of lymphoma in rats, because lymphocyte and plasma cell accumulation in the lung is characteristic of M. pulmonis disease, and because M. pulmonis disease can be exacerbated by experimental manipulations, including chemical treatment, we suggest that a plausible alternative explanation for the reported results of these bioassays is that the studies were confounded by M. pulmonis disease and that lesions of the disease were interpreted as lymphoma.

Abstract  Use of laboratory animals to identify carcinogenic potential of chemicals, mixtures, and other agents has a modern history of greater than 40 years from which much useful scientific and public health information can be derived. While laboratory animals differ from humans in some respects that may affect responses to hazardous exposures, use of such models is based on experimental evidence indicating that there are more genetic, genomic, physiological, biochemical, and metabolic similarities than differences among mammalian species. Issues of concordance of responses between rodent species and between rodents and humans as well as repeatability and site-specificity are important considerations in evaluating laboratory animal carcinogenicity results. Variables in experimental design such as animal strain, diet, route of exposure, and study duration as well as single-site versus multisite carcinogenic responses all influence interpretation and intelligent use of study data. Similarities and differences in site-specific laboratory animal and corresponding human cancers should also be considered in study evaluation. Recent attempts to explore genetically engineered mice and to humanize the mouse for more relevant identification of carcinogen hazard identification have yielded mixed results. In the end we are confronted by the realization that virtually all animal cancer models are useful but imperfect surrogates for humans. Assuming the percentage of chemicals currently in commerce that are estimated to be potent animal or human carcinogens is quite low, the task of identifying agents with significant carcinogenic potential is daunting and important. The biological conundrum of scientific debate regarding the relevance of carcinogenicity studies in laboratory animals is likely to continue. Nonetheless public health considerations must take precedence when deciding human safety issues.

Abstract  Aspartame (APM) or L-aspartyl-L-phenylalanine, and a 3 : 1 combination of APM with its decomposition product, 5-benzyl-3,6-dioxo-2-piperazine acetic acid (DKP), were incorporated at levels of up to 4 g/kg in the diet of male and female Wistar rats from 6 weeks to 104 weeks of age. There was a dose-dependent depression of body weight gain at 2 and 4 g/kg AMP and at 4 g/kg APM + DKP in males, and at all dose levels in females, correlated with decreased food consumption and attributed to liberation of amino acids from hydrolysis of APM. Increases in urinary specific gravity and pH, with increase of relative kidney weight, were attributed to the urinary excretion DKP and acidic metabolites of APM. A dose-related increase in urinary calcium probably reflected increased calcium absorption, as from high protein diets. A slight decrease in serum cholesterol and an increase in relative spleen weight appeared to be without adverse effect. It is concluded that the treatments were without toxic effect.

Abstract  An international, interdisciplinary working group of expert scientists met in June 2004 to develop IARC Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans (IARC Monographs) on formaldehyde, 2-butoxyethanol, and 1-tert-butoxy-2-propanol. Each IARC Monograph includes a critical review of the pertinent scientific literature and an evaluation of an agent's potential to cause cancer in humans. After a thorough discussion of the epidemiologic, experimental, and other relevant data, the working group concluded that formaldehyde is carcinogenic to humans, based on sufficient evidence in humans and in experimental animals. In the epidemiologic studies, there was sufficient evidence that formaldehyde causes nasopharyngeal cancer, "strong but not sufficient" evidence of leukemia, and limited evidence of sinonasal cancer. The working group also concluded that 2-butoxyethanol and 1-tert-butoxy-2-propanol are not classifiable as to their carcinogenicity to humans, each having limited evidence in experimental animals and inadequate evidence in humans. These three evaluations and the supporting data will be published as Volume 88 of the IARC Monographs.

Abstract  The rapid advances in the field of immunology and an understanding of the potential adverse effects of xenobiotics on the immune system have resulted in the development of a discipline in toxicology now referred to as immunotoxicology. This discipline has evolved steadily over the last 2 decades as a result of research in the national and international communities. Various US, European, and Japanese regulatory agencies have recognized a need to promulgate testing guidelines for immunotoxicity in support of the approval process involving toxicological testing. The US Food and Drug Administration "Redbook II" guidelines and some of the research conducted in support of the concepts and testing strategies are presented here. Concerns raised with regard to these guidelines are included, as are on-going initiatives in development of experimental approaches for assessing allergic potential and/or hypersensitivity responses to new foods and food constituents.