Which of the following is a common chemotherapeutic agent used in veterinary oncology?

Doxorubicin is a well-established chemotherapeutic agent commonly used in veterinary oncology. It belongs to the class of anthracycline antibiotics and is known for its efficacy against various types of tumors, including lymphomas and certain solid tumors in dogs and cats. Doxorubicin operates by interfering with the cancer cell's ability to replicate DNA, ultimately inhibiting their growth and proliferation.

In contrast, ibuprofen is classified as a nonsteroidal anti-inflammatory drug (NSAID) and is primarily used for pain relief and to reduce inflammation, but it does not have any chemotherapeutic properties. Amoxicillin is an antibiotic used to treat bacterial infections and is not effective against cancer cells. Prednisone, while a glucocorticoid with some use in cancer treatment for its immunosuppressive and anti-inflammatory effects, is not a chemotherapeutic agent in the same sense as doxorubicin. It may be used in conjunction with other treatments but does not directly kill cancer cells. Thus, doxorubicin stands out as the primary chemotherapeutic agent among the choices provided, specifically within the context of veterinary oncology.