Depending on whether the etiologic agent is known, neoplasms of poultry are divided into 2 main categories: virus-induced neoplasms and neoplasms of unknown etiology. There are 3 economically important virus-induced neoplastic diseases of poultry: Marek's disease, caused by a herpesvirus, and avian leukosis/sarcoma and reticuloendotheliosis, caused by retroviruses. While these neoplastic diseases cause economic losses from tumor mortality and poor performance, some of them have served as highly suitable models for studying neoplasia.

A rare neoplastic disease of turkeys known as lymphoproliferative disease that has been reported in Europe and Israel is induced by a retrovirus that is distinct from both the leukosis/sarcoma and reticuloendotheliosis viruses. The incidence of lymphoproliferative disease of turkeys has always been sporadic and therefore is not discussed in this chapter.

Neoplasms of unknown etiology are classified according to their morphologic characteristics; they include a wide variety of benign and malignant neoplasms. Of these tumors, only dermal squamous cell carcinoma, multicentric histiocytosis, and adenocarcinoma are discussed in this chapter.

Last full review/revision March 2012 by Aly M. Fadly, DVM, PhD, DACPV