Bone cancer (osteosarcoma) causes the death of many large and giant dogs. This study aims to identify the genetic mutations that increase the risk of Irish Wolfhounds developing osteosarcoma. The study may have an impact beyond the Irish Wolfhound, as osteosarcoma susceptibility genes found in the Irish Wolfhound may also be responsible for the predisposition of other breeds (Borzoi, Great Danes, Greyhounds, Rottweilers and Scottish Deerhounds) that have a high risk of developing osteosarcoma. If successful, the study will enable the development of a diagnostic test that would help breeders to reduce the number of dogs developing these tumours. The study will also increase understanding of the process by which bone tumours develop, and may lead to new treatments for affected dogs. Through the study, we will also test a new method for finding the gene defects that contribute to the development of complex diseases such as cancer.