Mammary fibroadenomas

In a study by MacEwen et al. (1977), groups of 40 male and 40 female Sprague-Dawley rats were exposed to 10 mg/m3 coal tar aerosol 6 hours/day, 5 days/week for 18 months. Control animals were held in a vivarium. After exposures, the animals were returned to the vivarium and held for an additional 6 months of observation prior to necropsy. The tumors found in rats exposed to coal tar aerosol showed 31 of 38 females and all males (38 of 38) with squamous cell carcinoma (lung) and 3 of 38 females with mammary fibroadenoma. Overall tumor incidences for controls were 0% for males and 13% for females. Overall tumor incidences for exposed animals were 100% for males and 82% for females. 

The number of mammary fibroadenomas per animal (multiplicity) and incidence was significantly decreased in 625 (15/50) and 1,250 ppm (7/50) BP-exposed female F344 rats compared with controls (27/50 ppm) (Rhodes et al. 2007). In addition, the incidence of mammary fibroadenomas in the 1,250 ppm group was less than half of that predicted by the historical controls firom dietary (feed) studies. Mammary fibroadenomas are a common spontaneous neoplasm in female rats. The authors note that other BP-based compounds have been identified as inhibitors of the steroid sulfatase, an enzyme that plays a role in the synthesis of estrone and conversion to estradiol. However, the actual mechanism by which BP or its metabolites may have reduced mammary tumor incidences in these cancer bioassays is not known. 

In a two-year rat carcinogenicity study with fluconazole, there was a decreased incidence of mammary fibroadenomas in females and adrenal phaeochromocytomas in males. These effects are also thought to be due to inhibition of steroidogenesis, through the inhibition of aromatase. ... 

Exposed rats also had elevated incidences of splenic hemangiosarcomas (both sexes), mesothelioma of the tunica vaginalis (males), pulmonary alveolar/bronchiolar adenoma or carcinoma (females), and fibroadenoma of the mammary gland (females). 

Two-year inhalation studies (6 hours/day, 5 days/week for 103 weeks) in rodents showed clear evidence of carcinogenicity. Mice exposed at 375 and 750ppm had increased incidences of harderian gland adenomas and carcinomas female mice exposed at 188 and 750 ppm had increased liver neoplasms female rats in the 188 and 375ppm-exposed groups had increased incidences of mammary gland fibroadenomas and carcinomas. Other treatment-related effects were an increase in nasal lesions and degeneration of the respiratory epithelium in mice. 

In 2 year carcinogenicity inhalation bioassays in rats and mice, there were no indications of carcinogenicity in male rats, while equivocal evidence was found in female rats. These findings were evidenced by increased fibroadenomas of the mammary gland. In these 2 year studies in mice, there was no evidence of carcinogenic activity in males and females. 

CN was investigated for oncogenic potential in a 2 year bioassay, in which rats were exposed to 0, 1, or 2 mg m , and mice to 0, 2, or 4 mg m (NTP, 1990a). Compound-related nonneoplastic lesions were seen in the respiratory tract of rats and mice. Neoplastic lesions were not seen in male or female mice or male rats, but female rats had an increase in mammary gland fibroadenomas, indicating equivocal evidence for carcinogenicity. 

Mammary gland Adenomas and fibroadenomas Sometimes Mann et al. (1996)... 

Mammary gland fibroadenomas and fibromas-fibrosarcomas of the subcutis Sometimes Bruner et al. (2001), Evans et til. (1997), ICRT (1993b), Mann et al. (1996)... 

In general, these tumors should not be combined, because they are thought to arise from different parts of the mammary gland. However, when an adenoma or carcinoma arises from a fibroadenoma, it should be combined with other adenomas and carcinomas of the mammary gland. 

Fibroadenomas and phyllodes tumors comprise the vast majority of fibroepithelial tumors of the breast, though mammary hamartomas and periductal stromal tumor are also considered in this category. 

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