Tumors and Your Dog

Mesenchymal tissue is made up of loosely associated cells, meaning this type of tissue can migrate easily. Because of its lack of polarity, mesenchymal tissue can sometimes form tumors on your dog’s body, and these tumors can spread to other areas, or proliferate. Only a veterinarian can determine if a tumor is malignant or benign. It’s essential to have your veterinarian examine your dog whenever you find an unusual growth on his body.

Mesenchymal Proliferation Tumors

Proliferation is defined as something that increases rapidly, and the types of mesenchymal tumors that proliferate can do just that. Lipomas, fibroma, fibrosarcoma, dermal hemangiosarcoma, and subcutaneous hemangiosarcomas are all canine mesenchymal tumors which can proliferate, or spread rapidly.


Lipomas are very common soft and fatty growths, which can proliferate in many areas of a dog’s body. Oftentimes, these growths are nothing to worry about, but you should contact your veterinarian so he can determine the growth is, in fact, lipoma. If you allowed lipoma to go unchecked by a veterinarian, you could be putting your dog in grave danger, as the tumor could be a more serious malignant cancer. If your veterinarian determines your dog has a lipoma growth, he’ll likely document it, and ask that you report any future changes in its size or location.


Fibroma is the name given to encapsulated benign tumors. These tumors occur when fibrocytes and collagen proliferate. Typically, fibromas will form on your dog’s skin, but can also form anywhere there is connective tissue. Fibroma may be difficult to detect, as these mesenchymal tumors are generally small, and will require a microscopic exam to determine if the growth is fibroma, or something else. Older female boxers are especially prone to fibroma, as are Boston terriers, Doberman pinschers, golden retrievers, and fox terriers.


Fibrosarcoma tumors are cancerous, and they proliferate aggressively, even after treatment. The malignant tumors are often found in middle-age to senior dogs, around the limbs. Early detection is essential, especially if your dog is under a year old. If you suspect your dog has a fibrosarcoma tumor, or any tumor, it’s essential to get him to the veterinarian right away. Your veterinarian will perform a physical exam, as well as blood work, to determine if your dog is suffering this aggressive cancer.

Dermal and Subcutaneous Hemangiosarcomas

About one-third of hemangiosarcomas will proliferate, so it’s important that these malignant tumors are treated quickly. Sun exposure is the leading cause of dermal hemangiosarcoma, which can be identified by small red or black growths on your dog’s skin. Subcutaneous hemangiosarcomas are red blood growths located under the skin. Both hemangiosarcomas usually occur in large breeds from middle-age to senior-age. If your veterinarian determines that your dog is suffering from hemangiosarcoma tumors, he may prescribe chemotherapy and/or surgery.

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