BMC Cancer 2007, 7:218 http://www.biomedcentral.com/1471-2407/7/218 IFmigmuurneo4histochemical aspects of E-cadherin membrane antigen stain; original magnification, 40× Immunohistochemical aspects of E-cadherin membrane antigen stain; original magnification, 40×.(A) Pleomorphic adenoma in human salivary gland with membrane E-cadherin stain; (B) Mixed tumour in canine mammary gland with membrane E-cadherin stain; (C) Carcinoma ex-pleomorphic adenoma in human salivary gland with evident loss of membrane E-cadherin marker; (D) Metaplastic carcinoma in canine mammary gland with evident loss of E-cadherin membrane marker. Note the loss of expres- sion in malignant tumours. tumours has been reported also by others [38,53-55]. One possible explanation would be the very low level expres- sion of this protein [56], with an mRNA transcription being observed, which was shown by the study of Lei- mola-Virtanen et al. [57], or difficulties in recognition of epitopes through immunohistochemistry. In this work, the absence of ER expression in human salivary gland tumours suggests that these lesions not very responsive to estrogen, in contrast to the lesions in dogs, but further studies should be carried out to better define the role this protein in salivary gland tumorigenesis. Conclusion In the present work, some clinical, histopathological and antigenic similarities were confirmed between mixed-type tumours from human salivary and canine mammary glands. These data could suggest a hypothesis of similar histogenesis between these neoplasias. More interestingly, it encourages the use of spontaneous canine mammary gland tumours as animal models to study human salivary gland mixed neoplasias. However, differences were also identified and, therefore, additional studies should be car- ried out to better define advantages and disadvantages of a comparative assessment between these lesions. Competing interests The author(s) declare that they have no competing inter- ests. Authors' contributions All authors contributed to the writing of the manuscript. All authors read and approved the final manuscript. Acknowledgements The authors would like to thank the Instituto Nacional do Câncer (INCA), Hospital do Câncer A. C. Camargo, Brazil for providing cases of Ca ex-PA, and Luiz Cosme Malaquias, PhD, from Universidade Vale do Rio Doce for having critically reviewed the paper. This work was supported in part by Fundação de Amparo à Pesquisa de Minas Gerais (FAPEMIG), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES). References 1. Lindblad-Toh K, Wade CM, Mikkelsen TS, Karlsson EK, Jaffe DB, Kamal M, Clamp M, Chang JL, Kulbokas EJ 3rd, Zody MC, Mauceli E, Xie X, Breen M, Wayne RK, Ostrander EA, Ponting CP, Galibert F, Page 7 of 9 (page number not for citation purposes)