Malignant mammary tumor in female dogs: environmental contaminants
© Andrade et al; licensee BioMed Central Ltd. 2010
Received: 8 October 2009
Accepted: 30 June 2010
Published: 30 June 2010
Mammary tumors of female dogs have greatly increased in recent years, thus demanding rapid diagnosis and effective treatment in order to determine the animal survival. There is considerable scientific interest in the possible role of environmental contaminants in the etiology of mammary tumors, specifically in relation to synthetic chemical substances released into the environment to which living beings are either directly or indirectly exposed. In this study, the presence of pyrethroid insecticide was observed in adjacent adipose tissue of canine mammary tumor. High Precision Liquid Chromatography - HPLC was adapted to detect and identify environmental contaminants in adipose tissue adjacent to malignant mammary tumor in nine female dogs, without predilection for breed or age. After surgery, masses were carefully examined for malignant neoplastic lesions. Five grams of adipose tissue adjacent to the tumor were collected to detect of environmental contaminants. The identified pyrethroids were allethrin, cyhalothrin, cypermethrin, deltamethrin and tetramethrin, with a contamination level of 33.3%. Histopathology demonstrated six female dogs (66.7%) as having complex carcinoma and three (33.3%) with simple carcinoma. From these tumors, seven (77.8%) presented aggressiveness degree III and two (22.2%) degree I. Five tumors were positive for estrogen receptors in immunohistochemical analysis. The contamination level was observed in more aggressive tumors. This was the first report in which the level of environmental contaminants could be detected in adipose tissue of female dogs with malignant mammary tumor, by HPLC. Results suggest the possible involvement of pyrethroid in the canine mammary tumor carcinogenesis. Hence, the dog may be used as a sentinel animal for human breast cancer, since human beings share the same environment and basically have the same eating habits.
Currently, mammary tumors represent 50% of all neoplasms that afflict female dogs [1, 2], and from these tumors 41 to 53% are of malignant character [3–5]. Epidemiological and clinical characteristics as well as biological behavior of such tumors in female dogs are similar to breast carcinomas in women, for this reason female dogs present an excellent comparative model to understand various aspects of carcinogenesis in both species . It is believed that mammary neoplasias may occur as a result of complex interactions of distinct factors; however the exact cause is still under research. Through this dynamic process, the mammary tumor can be influenced by internal host factors such as genetics and external factors, including environmental contamination, that can enable or reduce the individual response [7–9]. The pyrethroids are among environmental contaminants the ones whose use has exponentially grown in recent years . They are used to control pests in agriculture, ranching and domestic animals. The overspread use of this contaminant is associated with its efficiency in pest control and its relatively short half-life [11–13]. In humans and other animals, pyrethroids are readily absorbed cutaneously and also in the digestive and respiratory tracts. Once absorbed they are distributed to various tissues, but they are concentrated especially in the adipose tissue. International Agency for Research Cancer (IARC) includes agrotoxins, especially deltamethrin and cypermethrin in group 3 of risk level, that is, non-conclusive carcinogenic for humans, while the World Health Organization (WHO) classifies deltamethrin as a moderately dangerous insecticide [14, 15]. Considering that this research line is still not used in regular basis for the veterinary medicine, the present study aimed to detect and identify levels of pyrethroid insecticides in adipose tissue adjacent to malignant mammary tumor in female dogs by the HPLC method and correlate these contaminants with the aggressiveness degree of the neoplasias.
Material and Methods
Veterinary and Human histopathological classification of Malignant mammary tumor in female dogs showing their malignity, positive immunemarking for estrogen receptors, and pyrethroid identification with their respective concentration levels in the analyzed samples
Classification - Carcinoma
It is very little the number of studies connecting steroid hormone receptors and mammary tumors in female dogs. However, some human and canine carcinogenic hormone aspects seem to be similar. Toxicological and Epidemiological studies have shown that steroid hormones and synthetic derived trigger the development of mammary gland, suggesting that they may play an important role in the canine mammary tumor pathogenesis .
Epidemiological studies and tests on rodents have demonstrated the influence of environmental contaminants on neoplasia development, including breast cancer [10, 25, 26]. Garey et al, (1998)  emphasized that pyrethroids can induce a breakdown in the homeostasis of hormones such as estrogens and indirectly influence cell proliferation or apoptosis, either increasing or diminishing them in mammary epithelial cells, thereby triggering the neoplastic process. Results obtained in the present study detected the presence of 33.3% of pyrethroid pesticides in adipose tissue of female dogs with mammary carcinoma.
In order to improve results, and collection of data, our group is still researching such environmental contamination, increasing the number of samples as well as including samples from control animals.
We acknowledge CAPES and FAPESP (2008/57.309-5) for the financial support.
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