Hyperplastic lesion

Rats and mice were exposed 6 hours/day, 5 days/week for 2 years at 2 or 5 ppm or 0.5 or 2 ppm, respectively Tetranitromethane was found to cause mild irritation and hyperplastic lesions in the nasal passages. Nearly all animals exposed at the higher dose levels developed alveolar/bronchiolar adenoma or carcinoma squamous cell neoplasms of the lung also occurred in exposed rats. The carcinogenic activity of tetranitromethane appears to be the result of chronic epithelial irritation mitotic stimulation and ensuing hyperplastic response. ... 

The characteristics of the nasal lesions in mice following chronic inhalation of ethylene dibromide were investigated. Male and female B6C3F, mice were exposed to 10 or 40 ppm [77 or 308 mg/m- ] ethylene dibromide for 6 h per day on five days per week for 103 (10 ppm) or 90 (40 ppm) weeks. The incidence of hyperplastic lesions was related to the dose of ethylene dibromide and was equivalent in males and females. Lesions consisted of focal areas of cuboidal to columnar cells arranged in a glandular pattern with foci of hyperplastic squamous epithelium also seen occasionally. Lesions were usually located in the anterior (respiratory turbinates) of the nasal cavities. A broad spectrum of proliferative lesions was observed (Stinson et al., 1981). 

Methyl bromide was tested by oral administration in rats and by inhalation in mice and rats. In one 90-day study by oral administration in rats, methyl bromide was reported to produce squamous-cell carcinomas of the forestomach. In a second, 25-week study designed to investigate further the findings of the previous study, early hyperplastic lesions of the forestomach developed after 25 weeks of continuous treatment by gavage. In two inhalation studies in mice, no significant increase in the incidence of tumours was observ ed. In one inhalation study in rats, an increase in the incidence of adenomas of the pituitary gland was observed in high-dose male rats. In another study in rats, no increase in tumour incidence was observed. 

Groups of BD IX rats sex not specified] received a single subcutaneous injection of 40 mg/kg bw 1,2-dimethylhydrazine at the age of one day (11 rats), 10 days (7 rats) or 30 days (13 rats). The rats lived until their natural death. Among 11 rats treated at one day of age, one developed a colon carcinoma, with no dysplasia or hyperplasia in other rats. Among rats treated at the age of 10 days, 3/7 developed 4 colon carcinomas. One rat had a dysplasia and another had a hyperplasia. Four of 13 rats treated at the age of 30 days developed 13 carcinomas and three rats developed carcinomas of the small bowel. Six rats had dysplastic and four rats hyperplastic colon lesions. One rat had a dysplastic lesion and one a hyperplastic lesion of the small bowel (Martin et al., 1974). 

Similarly, no respiratory effects were found in rats and mice chronically exposed by diet to 5/ 10" and 1.3 10s g/kg/day of 2,7-DCDD, respectively (NCI/NTP 1979a). In contrast, rats exposed chronically by gavage to a mixture of 1,2,3,6,7,8-HxCDD and 1,2,3,7,8,9-HxCDD at 0.18, 0.34, and 0.7 g/kg/day had a dose-related increased incidence of adenomatous hyperplastic lesions in terminal bronchioles and adjacent alveoli of both males and females no such effects were found in mice exposed chronically to 0.7 g/kg/day of that same mixture (NCI/NTP 1980). The existing information suggests that in animals, the respiratory system is not a sensitive target for CDDs toxicity via oral exposure. 

Early papillomas (10 wks) during promotion are well differentiated hyperplastic lesions with either mild or no cellular atypia, whereas late ones (40 wks) are dysplastic, show atypia and are aneuploid. 

Polyps between 6 and 9 mm are defined as intermediate lesions. Most of them are eventually found to be low-grade dysplasia adenomas, less than 1% are found to be harbour invasive carcinomas and 30% are found to be hyperplastic lesions. Thus, surveillance either with conventional or virtual colonoscopy may be a reasonable option in these cases... 

Solt, D. B., Medline, A., and Farber, E., 1977, Rapid emergence of carcinogen-induced hyperplastic lesions in a new model for the sequential analysis of liver carcinogenesis. Am, J. Pathol 88 595. 

Small sessile polyps frequently represent hyperplastic polyps. Hyperplastic lesions tend to flatten out in well distended segments, explaining the fact that those lesions might only be visible in somewhat underdistended segments. In that way, those lesions are frequently only recognised on either prone or supine position, and can therefore be mistaken as residual stool. 

Hyperplastic lesions however are not to be considered precancerous, and should therefore be considered as "leave-alone lesions. Misinterpreting those lesions as residual stool is therefore rather beneficial for the patients, avoiding unnecessary conventional colonoscopy (Pickhardt et al. 2004a) (Fig. 8.17). 

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