Frequently Asked Questions About Chemotherapy in Cats & Dogs 

What is chemotherapy?

Chemotherapy agents are medications that kill cancer cells. These medications may be given intravenously (into the vein) or by mouth on an outpatient basis. Some chemotherapy treatments are available as daily pills that can be given at home. 

The goal of chemotherapy is to control a pet’s cancer and prolong their life while maintaining a good quality of life at home. 

When is chemotherapy recommended for pets?

Chemotherapy is typically used for: 

• Pets with cancers in which chemotherapy is the treatment of choice, such as lymphoma and leukemia 
• After surgical removal of a primary tumor that has a high likelihood of spreading to other areas of the body. For example, bone cancer, hemangiosarcoma, and high-grade mast cell tumors. 
• Pets with non-surgical tumors in which the goal is to delay growth and control clinical signs, such as metastatic mast cell tumors, thyroid carcinomas, and bladder tumors. 

What side effects can chemotherapy cause in cats and dogs?

The priority in veterinary oncology is to address a patient’s cancer with therapy that minimizes their side effects and optimizes their quality of life.  

Most chemotherapy agents work by affecting rapidly dividing cells which can affect the cells of the gastrointestinal (GI) tract. However, approximately 80-85% of patients have minimal to no side effects from chemotherapy. About 15-20% of patients may have side effects that require supportive medications at home. These medications may include treatments to alleviate nausea, manage diarrhea or boost the appetite. Fewer than 10% require hospitalization.  

Lab work is closely monitored during chemotherapy. A patient’s cell counts may decrease secondary to chemotherapy putting them at risk of an infection. This may lead to additional treatment with antibiotics and potentially a delay in treatment to allow their cell counts to rebound. In addition, throughout chemotherapy, the patient’s overall health will be monitored with lab work to evaluate the organ function and ensure they remain healthy.   

Overall, most veterinary patients tolerate chemotherapy very well and maintain or regain an excellent quality of life during the treatment protocol.  

Will my cat or dog lose their hair?

Most dogs and cats do not have any hair loss secondary to chemotherapy. However, clipped fur may regrow slowly, and some breeds that require grooming, such as Poodles, Schnauzers, and Bichon Frises, can develop hair loss or skin pigment change to varying degrees. Additionally, cats may lose their whiskers. Lost hair will usually regrow after discontinuation of chemotherapy, although it may differ in color and texture.