Ancillary Antineoplastic Agents
Supplementary agents are occasionally used in veterinary oncology to either enhance the effect of certain chemotherapy treatments or support the well-being of the patient. Drugs in this category include antiemetic therapy, prophylactic antibiotics, COX-2 inhibitors (NSAIDs), and various pain medications.
Bisphosphonates are frequently used in veterinary oncology for a variety of reasons, including to treat bone pain from primary bone tumors or bone metastasis, and to effectively treat hypercalcemia of malignancy. Bisphosphonates belong to a class of drugs that directly inhibit osteoclast activity and the subsequent resorption of bone. In people, these drugs are used for various conditions that are characterized by bone resorption and bone fragility, such as osteoporosis. In addition to their inhibitory effects on osteoclasts, bisphosphonates are believed to exert direct cytotoxic effects on some cancer cells. These effects include induction of apoptosis, inhibition of new blood vessel formation, and reduction of tumor cell adhesion to bone matrix.
Retinoids are a class of compounds structurally related to vitamin A. In preclinical studies, all-trans retinoic acid (tretinoin), 13-cis retinoic acid (isotretinoin), and the aromatic retinoids etretinate and acitretin have preventive and therapeutic effects on carcinogen-induced premalignant and malignant lesions in both human and veterinary medicine. Isotretinoin and etretinate have been used with limited therapeutic success in superficial squamous cell carcinoma and cutaneous lymphoma. In people, dramatic therapeutic effects have been observed in treatment of acute promyelocytic leukemia with tretinoin. The mechanism of action of retinoids is thought to occur through modulation of cell proliferation and differentiation. Retinoids vary in their capacity to induce differentiation and to inhibit proliferation in a variety of human and veterinary cell lines.