Cancer is no longer an immediate death sentence for animals.

Advances in veterinary oncology now allow dogs, cats, and even wild animals such as coyotes to receive specialized treatments such as radiation therapy and chemotherapy, explained Dr. Manuela Mora, medical director and veterinary oncologist at the Center for Veterinary Oncology and Radiotherapy.

So much so that response rates in many cases allow for a significant prolongation and improvement in the animals’ quality of life, added the specialist.

However, the decision to use radiotherapy or chemotherapy depends on the type of tumor, its location, and the animal’s general condition. The objective of the treatment also comes into play: to cure, control, or simply provide comfort (quality of death).

In addition, some owners prefer that their pet receive only radiation therapy and not chemotherapy.

When is radiation therapy used?

Radiation therapy uses ionizing radiation to destroy tumor cells or reduce their size. It is mainly recommended in:

• Localized tumors that cannot be completely removed by surgery.

• Cancers in delicate areas such as the brain, nasal cavity, or spinal cord.

• Cases where residual tumor tissue remains after surgery.

• Skin tumors or aggressive mast cell tumors.

In dogs and cats, radiation therapy is usually administered in scheduled sessions under sedation or light anesthesia to prevent movement. The goal may be curative or palliative (to relieve pain and pressure caused by the tumor).

When is chemotherapy used?

Chemotherapy is used when the cancer is systemic or has a high probability of spreading (metastasis). It is common in cases such as:

• Lymphoma (one of the most common cancers in dogs).

• Leukemia.

• Mammary tumors with metastasis.

• Sarcomas and other aggressive tumors.

Unlike humans, veterinary medicine prioritizes quality of life over aggressive treatment. For this reason, doses are usually lower and side effects—such as vomiting or hair loss—tend to be milder. Most animals tolerate the treatment well, said the specialist.

Which breeds are most susceptible?

Some breeds have a greater genetic predisposition to developing tumors.

Among those most frequently cited by international veterinary studies, and mentioned by the head of the Center for Veterinary Oncology and Radiotherapy, are:

• Golden Retriever (high incidence of lymphoma and hemangiosarcoma).

• Boxer (mast cell tumors and skin tumors).

• Rottweiler (osteosarcoma).

• German Shepherd (various types of hematological cancer).

• Labrador Retriever (lymphoma and skin tumors).

• In cats, lymphoma and mammary tumors are the most common, especially in unspayed females.

When asked whether these breeds can overcome cancer, the answer depends on the type of tumor and the timing of diagnosis.

In canine lymphomas treated with chemotherapy, up to 80–90% can go into temporary remission, with average survival rates of 8 to 14 months, and even longer in some cases.

Tumors detected early and treated with surgery plus radiation therapy may have favorable prognoses.

In advanced cases, treatment may not be curative, but it can relieve pain and prolong life with good quality, the veterinarian emphasized.

The key factor, she said, is early detection: changes in appetite, lumps, abnormal bleeding, weight loss, or persistent fatigue should prompt immediate consultation.

What about wild animals?

Radiotherapy and chemotherapy have also been used in rescue centers and specialized veterinary hospitals to treat wild cats, primates, and other animals under human care.

Although not common, these treatments can be an option when the goal is conservation, welfare, or reproduction of valuable species.

Mora recounted the case of a coyote that required care at his center:

“A few days ago, we were contacted by a foundation that rescued a coyote with a tumor, called soft tissue sarcoma, at the base of its tail. It was a large mass… if I had to compare it to something, it could be compared to an orange.

“The problem we have with these tumors, whether they occur in wildlife or in dogs or cats, is that they are tumors that, even though they metastasize, are sometimes very locally invasive.

“Intracranial tumors in dogs or cats, meningiomas, or any other tumor inside the skull, since it is not possible to access and remove them, so in those cases, what we do is recommend radiation therapy as the first line of treatment,” he said.