is a primary bone cancer most frequently found in large or giant breeds of dogs. It is an aggressive cancer, often metastasising into secondary malignancies throughout the dog's body. It is probably the most common cancer found in the Leonberger.
is an aggressive and highly invasive form of cancer that targets blood vessels initially, but can then spread rapidly. The most common locations for the cancer are the blood supplies to the spleen, heart, liver and occasionally near or on the skin. It is a relatively common form of cancer in dogs, and has been known to affect the Leonberger breed. Dogs with hemangiosarcoma rarely show clinical signs until the tumour has become very large and has metastasized, by which time secondary cancers will usually be present.