Other Types of Tumors

In addition to the above-mentioned examples of tumors with disputed relevance to humans, mammary tumors in mice have been regarded as being of uncertain relevance for humans. The incidence of mammary tumors in mice has been shown to be highly influenced by environmental factors such as stress (Riley 1975), which complicates the interpretation of increased mammary tumor incidence in a carcinogenicity study. 

Phaeochromocytoma (a tumor in the adrenal medulla) is not uncommon in rats, but rare in humans. Pheochromocytomas are induced in rats by a variety of non-genotoxic substances that may act indirectly by stimulating chromaffin cell proliferation. They are not known to be similarly inducible in other species. In the rat, a mechanism for the development may be hypercalcaemia (Tischler et al. 1999 Capen et ah, in Haschek et al. 2001). 

Chemical substances, which are injected into laboratory animals, may cause tumors locally at the injection site, e.g., in the muscle, irrespective of the mechanism for the tumor formation. It is now well established that smooth-surfaced foreign bodies, regardless of their chemical composition, will produce sarcomas when transplanted subcutaneously into rodents (Moore 1991). It is difficult to evaluate the relevance for humans of such site-related tumor formation this issue has been further addressed by lARC (1999b). 

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Such low-dose extrapolation is typically only conducted for tumors believed to be caused by a genotoxic effect, which some, but by no means all, scientists believe have no threshold. For other types of tumors and for many nonneoplastic endpoints a threshold cannot be estimated directly from data at a limited number of dose levels a no observed effect level (NOEL) can be estimated by finding the highest dose level at which there is no significant increase in effects. 

Importantly, defects in MMR have been found in colon tumors and other types of tumors in patients that have no known hereditary predisposition to cancer. These are referred to as sporadic forms of cancer. It is thought that in these cases, patients are born with both alleles of a MMR gene intact. However, during there lifetime they acquire mutations in both alleles. This, at least in part, may explain differences in the age of onset of colon cancer in HNPCC patients It usually occurs when patients are in their forties and hfties, but sporadic cases tend to occur after people reach the age of 70. 

Breast and ovarian cancer share responsiveness to steroid hormones, and incidence of the vast majority of tumors in the epithelial rather than the stromal component. In addition, these diseases appear to share etiologic factors Women with one kind of tumor have an increased risk of developing the other type of tumor. Whereas normal ovarian tissue does not overexpress ErbB-... 

Flow cytometry A method of measuring the number of cells in a sample, the percentage of five cells in a sample, and certain characteristics of cells, such as size, shape, and the presence of tumor markers on the cell surface. The cells are stained with a light-sensitive dye, placed in a fluid, and passed in a stream before a laser or other type of light. The measurements are based on how the light-sensitive dye reacts to the light. 

The lead-induced nephropathy observed in humans and rodents shows a comparable early pathology (Goyer 1993). However, in rodents, proximal tubular cell injury induced by lead can progress to adenocarcinomas of the kidney (see Section 2.2.3.8). The observation of lead-induced kidney tumors in rats may not be relevant to humans. Conclusive evidence for lead-induced renal cancers (or any other type of cancer) in humans is lacking, even in populations in which chronic lead nephropathy is evident. 

Kimura, I., Miyake, T., Kubota, S., Kamata, A., Morikawa, S. and Ito, Y. Adenomatous polyps in the stomachs of hatchery-grown salmonids and other types of fishes. Prog. Exp. Tumor Res. (1976) 20, I8I-I9U. 

Substances such as promoters that interfere with cell-to-cell communication allow cancer cells to proliferate wildly. But cell proliferation can be induced by other means as well. Toxicity or other types of injury to tissues can result in a proliferative response. So can certain natural and synthetic hormones, such as estrogens, cause proliferation of certain tissues, such as the breast. Chronic viral infections may cause cell killing and its consequence is cell proliferation. It appears that sustained chronic proliferation induced in any of these ways, either by agents foreign to the body or some, such as the estrogens, that are natural to it, can increase tumor growth. 

The five intermediate filaments and their respective tissues are listed in Table 3. Only the intermediate filament, cytokeratin, is selected as useful in the initial classification of tumors. The other intermediate filaments can cause diagnostic confusion because (1) they are usually not expressed in their poorly differentiated counterparts (especially GFAP, NFP, and Desmin) and (2) they are often coexpressed on many types of tumors. Poorly differentiated neuroectodermal tumors may often express more than two intermediate filaments. Vimentin demonstrates the most lineage infidelity. 

Patients with other types of unresectable cancer also may benefit from chemotherapy, as evidenced by prolongation of life, shrinkage of tumor, and improvement in symptoms. Notable among these are ovarian epithelial and breast carcinomas, oat cell (small cell undifferentiated) carcinoma of the lung, and acute myelocytic leukemia. Cancers that are for the most part resistant to today s agents include melanoma, colorectal and renal carcinomas, and non-oat cell cancers of the lung. 

If phlegm accumulates over a long period of time, if combined with other pathogenic factors it can form masses and can present as different types of tumor. 

Methylation at C-4 of sterol nucleus was one of the other factors affecting activity enhancement. Thus, in general, 4-methylsterols (14,15) and 4,4-dimethylsterols (8,13) exhibited higher activity than 4-desmethylsterols. A similar structure-activity relationship was observed also in the HHPA-induced inflammation on mouse ear [35]. Whereas cholesterol (7) did not show inhibitory activity, several 4,4-dimethylcholestane derivatives, 0-12, exhibited activity. 4,4-Dimethylcholestane-3a,5a-diol (12) was the most potent inhibitor its activity was comparable to that of ursolic acid (210) [35]. Compound 12 reduced also the inflammation induced by teleocidin B (3), one of the indole alkaloid-type of tumor promoters [53]. 

The most convincing evidence for the importance of cytoplasm on nuclear development comes from studies on teratoma, a unique type of tumor found in many kinds of mammals. It is composed both of neoplastic cells, like other tumors, and of many kinds of differentiated cells. A typical teratoma may include nerve, muscle, blood, and skin cells, and other differentiated cells all mixed together with undifferentiated neoplastic stem cells. Only the stem cells are neoplastic, producing more stem cells or more differentiated cells, usually both. In many ways the stem cells behave like... 

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