Depending on whether the etiological agent is known, neoplasms of poultry are divided into two main categories: virus-induced neoplasms and neoplasms of unknown etiology.
There are three economically important virus-induced neoplastic diseases of poultry: Marek's disease, caused by a herpesvirus, and avian leukosis/sarcoma and reticuloendotheliosis, caused by retroviruses. Although these neoplastic diseases cause economic losses from death and poor performance, some of them have served as highly suitable models to study neoplasia.
Additionally, a rare virus-induced neoplastic disease of turkeys known as lymphoproliferative disease has been reported in Europe and Israel. Lymphoproliferative disease is induced by a retrovirus that is distinct from both the leukosis/sarcoma and reticuloendotheliosis viruses. Although this virus has been detected by PCR assay in a small number of wild turkeys in the US and Canada, the incidence of the disease has always been sporadic.
Neoplasms of unknown etiology are classified according to their morphological characteristics. They include a wide variety of benign and malignant neoplasms, including dermal squamous cell carcinoma (avian keratoacanthoma), multicentric histiocytosis, and adenocarcinoma.
