Five canine malignancies that respond to chemotherapy

Cancer is a notoriously difficult group of diseases to treat and it is often difficult to be able to advise pet owners if it is worth their while to start medical therapy (i.e., chemotherapy). Here are five common cancer types for which there is good evidence that chemotherapy makes a difference in survival outcomes.

1. Lymphoma: Lymphoma is one of the most common malignancies in dogs and is highly responsive to chemotherapy. Untreated, the median survival time is 4-6 weeks. The standard of care treatment regimen involves multi-agent chemotherapy protocols, such as CHOP (Cyclophosphamide, Doxorubicin, Vincristine, and Prednisolone). Dogs treated with chemotherapy often achieve complete remission, with a median survival time (MST) ranging from 10 to 14 months. Approximately 80-90% of dogs will achieve remission with CHOP, making it a cornerstone in lymphoma treatment (1).

 2. Mast Cell Tumours: Mast cell tumours (MCTs) are the most common cutaneous tumours in dogs. High-grade MCTs or those that cannot be completely excised surgically are typically treated with chemotherapy, with toceranib (Palladia), vinblastine and lomustine (CCNU) most frequently used. A combination of surgery and chemotherapy can significantly improve outcomes, particularly in high-grade cases, with a MST of around 11 months and extending beyond two years for some dogs (2). Untreated, dogs with high grade MCTs have a MST of 4-5 months (3).

 3. Osteosarcoma: While surgery (amputation or limb-sparing techniques) is the primary treatment for osteosarcoma, chemotherapy is critical in managing metastatic disease, which is all but expected in this aggressive malignancy. The most commonly used chemotherapeutic agent is carboplatin. Dogs treated with both surgery and chemotherapy have a MST of 10-12 months (4), compared to 4-6 months with surgery alone (5).

 4. Haemangiosarcoma: Haemangiosarcoma is a highly malignant cancer of the blood vessels, often affecting the spleen. Surgery is typically the first step, but chemotherapy is essential due to the high likelihood of metastasis. Doxorubicin is the drug of choice, and while the prognosis is guarded, chemotherapy can extend survival by a number of months (6).

 5. Transitional Cell Carcinoma: Transitional cell carcinoma, now more frequently referred to as urothelial carcinoma, primarily affects the bladder, is another malignancy that benefits from chemotherapy, especially when surgical options are limited. Mitoxantrone, vinblastine and piroxicam are often used, with some dogs experiencing prolonged survival in excess of 12 months. Chemotherapy helps in reducing tumour size, alleviating symptoms, and improving quality of life (8).

 Whilst chemotherapy is not always curative, it can significantly prolong survival in many cases, with life quality preserved in the hands of a sensitive clinician. By understanding the potential benefits and carefully tailoring treatments, veterinarians can make a meaningful difference to their cancer patients.

1.     Garrett LD, Thamm DH, Chun R, Dudley R, Vail DM. Evaluation of a 6-month chemotherapy protocol with no maintenance therapy for dogs with lymphoma. J Vet Intern Med. 2002 Nov-Dec;16(6):704-9.

2.     Cooper M, Tsai X, Bennett P. Combination CCNU and vinblastine chemotherapy for canine mast cell tumours: 57 cases. Vet Comp Oncol. 2009 Sep;7(3):196-206. 

3.     Burge R, Woolard KD, Willcox JL, Rebhun RB, Burton JH, Al-Nadaf S, Skorupski KA. High-Grade, Stage 2 Mast Cell Tumors: Outcome in Dogs With Local and Systemic Therapy. J Am Anim Hosp Assoc. 2023 Jul 1;59(4):167-176. 

4.     Skorupski KA, Uhl JM, Szivek A, Allstadt Frazier SD, Rebhun RB, Rodriguez CO Jr. Carboplatin versus alternating carboplatin and doxorubicin for the adjuvant treatment of canine appendicular osteosarcoma: a randomized, phase III trial. Vet Comp Oncol. 2016 Mar;14(1):81-7. 

5.     Straw RC, Withrow SJ, Richter SL, Powers BE, Klein MK, Postorino NC, LaRue SM, Ogilvie GK, Vail DM, Morrison WB, et al. Amputation and cisplatin for treatment of canine osteosarcoma. J Vet Intern Med. 1991 Jul-Aug;5(4):205-10. 

6.     Sorenmo KU, Baez JL, Clifford CA, Mauldin E, Overley B, Skorupski K, Bachman R, Samluk M, Shofer F. Efficacy and toxicity of a dose-intensified doxorubicin protocol in canine hemangiosarcoma. J Vet Intern Med. 2004 Mar-Apr;18(2):209-13. 

7.     Arnold EJ, Childress MO, Fourez LM, Tan KM, Stewart JC, Bonney PL, Knapp DW. Clinical trial of vinblastine in dogs with transitional cell carcinoma of the urinary bladder. J Vet Intern Med. 2011 Nov-Dec;25(6):1385-90.