In this retrospective study, immunophenotypic analysis supported a diagnosis of B-cell chronic lymphocytic leukemia (CLL) in 2 dogs, and 1 dog was tentatively diagnosed with T-cell CLL. All of the dogs had high lymphocyte counts (26.4 to 97.8 x 109/L), with mature-appearing cells reported. The dogs were treated with melphalan and prednisolone. Case 1: A 5-year-old Yorkshire terrier was given melphalan (3 mg/m2 body surface area [BSA]) and prednisolone (20 mg/m2 BSA) by mouth. It was also given an antibiotic and ursodeoxycholic acid. Clinical signs and hematologic findings gradually improved, and on the 8th day melphalan was discontinued and the prednisolone was decreased to 15 mg/m2 BSA every other day and then decreased again on the 30th day and the 120th day. Two years after admission, the dog remained clinically normal and lymphocyte count was within the normal range. Case 2: A 10-year-old Shih Tzu. Treatment began with once-a-day, oral melphalan (3 mg/m2 BSA) and prednisolone (20 mg/m2 BSA), in addition to antibiotics. The dose of prednisolone was decreased to 6.6 mg/m2 on the 10th day. After 91 days, the melphalan and prednisolone were tapered to every other day and then discontinued on the 210th day. At 302 days after admission, the lymphocyte count was still reduced. Case 3: A 7-year-old Bernese mountain dog was started on melphalan (3 mg/m2 BSA) once a day. Prednisolone (8.5 mg/m2 BSA) was started on the 8th day. Prednisolone was decreased on the 29th day; melphalan was increased to 4 mg/m2 BSA on day 43 and then to 5 mg/m2 BSA on the 64th day. Melphalan was reduced to every other day on the 92nd day and discontinued on the 127th day. Prednisolone was decreased and discontinued by the 141st day. When the dog was evaluated on the 190th day after admission, lymphocyte counts were high, so the drugs were reintroduced on the every-other-day schedule. At day 267, the lymphocyte count was within normal limits.

COMMENTARY: Melphalan is an alkylating agent that has been used to treat plasma cell tumors in dogs with few side effects. Although it is cytotoxic, therapeutic levels do not affect phagocytic activity in human leukocytes, although some other chemotherapeutic drugs may impair that ability. It is possible that dogs with CLL have impaired immune function, so a drug that reduces the risk for clinical infections would be advantageous. The most effective dose of this drug in treating dogs with CLL still needs to be studied.

Treatment of chronic lymphocytic leukaemia in three dogs with melphalan and prednisolone. Fujino Y, Sawamura S, Kurakawa N, et al. J SMALL ANIM PRACT 45:298-303, 2004.