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Canine Infiltrative Lipomas

Infiltrative lipomas (tumors arising from fat cells, which are also called adipocytes) are uncommon in dogs and cats with limited information available in the veterinary literature. Simple lipomas are benign, well encapsulated, and can often be cured with surgery. However, infiltrative lipomas are very locally invasive and have a high tendency to recur following surgery but do not tend to metastasize (spread to other parts of the body). The infiltrative nature of these tumors means that the tumor invades deep tissue structures such as muscle, nerves, and bone, which is why surgical removal is difficult and sometimes impossible.

Dogs with infiltrative lipomas are staged with bloodwork, chest x-rays, and sometimes a CT or MRI depending on the location of the tumor. In cases of an operable tumor, it is recommended that a surgery is performed first to debulk the mass. Due to the locally invasive nature of this tumor, it is unlikely that surgery alone will be curative (except in certain cases were an aggressive surgery such as an amputation could be performed). The literature shows that surgery alone results in a recurrence rate of ~40% and half of the dogs experience tumor recurrence within 8 months. The dogs treated with surgery alone lived roughly 18 months.

Consequently, it is recommended to follow gross/marginal surgical removal of a tumor with radiation therapy post-op to maximize the chances of shrinking any remaining tumor and preventing it from recurring. In one study, 50% of dogs who received surgery (gross tumor removal) and radiation therapy survived longer than 40 months. Radiation can be administered to bulky tumor but is most effective for minimal disease.   Chemotherapy is not typically warranted for these tumors due to the limited metastatic potential of this tumor type. In some cases, however, low dose therapy designed to prevent blood vessel development may be used in attempt to prevent tumor recurrence by limited blood supply to the tumor cells.