Hemangiosarcoma is a common cancer of middle-aged to older dogs that targets the spleen in 50% of those affected. In fact, it’s the most common tumor of this organ. Less commonly, this cancer can manifest as tumors of the heart, lining of the heart (pericardium), skin, and the tissues underlying the skin. Other sites include the lungs, kidneys, mouth, muscle, bone, bladder, and uterus. Like many aggressive cancers, hemangiosarcoma tumors can also metastasize to other organs.

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