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Recommended by C. Cousens and S. Siso
Pathobiology Academic Program, School of Veterinary Medicine, St. George's University, P. O. Box 7, Grenada, West Indies
Received 11 November 2011; Accepted 8 December 2011
1. Introduction
Surveys on skin diseases of dogs demonstrate that neoplastic tumors of the skin are common [1-3]. Several studies report that in dogs the skin is the most commonly affected organ for both neoplastic and nonneoplastic tumors [4-7]. In one study, skin neoplastic and nonneoplastic tumors ranked second only to mammary gland tumors [8].
It has long been recognized among human populations that incidence rates and relative frequencies for several types of neoplasms differ markedly by geographic region [9]. Although studies on cutaneous neoplasms of dogs from different geographic regions report similarities, differences in tumor types and relative frequencies have also been reported. Such studies include those from the United Kingdom [10]; Greece [11]; United States of America [6]; Australia [12]; Korea [13]; Thailand [7]; Brazil [14]; Zimbabwe [15]; India [16]; Zambia [17]. For example, cutaneous histiocytoma was the most frequently reported neoplasm in dogs in India and Zambia [16, 17]; lipoma was the most common skin tumor in dogs in Korea [13], and mast cell tumor ranked first in studies on dogs from the United States, Thailand, the United Kingdom, Greece, Brazil, and Zimbabwe [6, 7, 10, 11, 14, 15]. Transmissible venereal tumor in the skin was only reported in studies from Korea and Brazil [13, 14]. Studies on canine nonneoplastic skin tumors have also reported differences in types and in frequency of these tumors. For example, studies from Korea, Thailand, and Brazil report that epidermal and follicular cysts are the most common nonneoplastic tumors affecting the skin of dogs followed by sebaceous hyperplasia, whereas a study from Serbia reports only the occurrence of dermoid cysts [7, 8, 13, 14].
Although geographic differences for the types and frequencies of canine cutaneous neoplastic and nonneoplastic tumors are recognized, the reasons for these differences are not well understood. For some types of cutaneous tumors it is likely that both climate and the breeds of dogs in respective locations play a role. Ultraviolet radiation from sunlight has been implicated as a risk factor for canine cutaneous hemangiosarcoma, hemangioma, and squamous cell carcinoma [18,...