Outcomes of pituitary tumor irradiation in cats.

Information on tumor control and normal tissue effects of radiotherapy to treat pituitary tumors in cats is limited. Radiation therapy is effective in controlling the clinical signs associated with pituitary tumors in cats, with a low incidence of adverse effects. Eight cats were irradiated at Colorado State University between 1991 and 2002 for spontaneous pituitary tumors. A retrospective review of records was made to assess tumor control and incidence of radiation-induced adverse effects. Pituitary carcinoma was diagnosed in 2 cats and pituitary adenoma in 6 cats. Total radiation dosage ranged from 4,500 to 5,400 cGy administered Monday through Friday in 270 or 300 cGy fractions. Acute effects were limited to epilation and mild otitis externa. Focal brain necrosis adjacent to regrowth of a pituitary carcinoma and a second tumor in the radiation field were reported as possible late effects. Median survival, regardless of cause of death of the 8 cats, was 17.4 months (range, 8.4 to 63.1 months). Median survival could not be determined if cats were censored for non-tumor-related causes of death. Six cats were alive at 1 year, and 3 cats were alive at 2 years after treatment. Tumor recurrence was seen in 1 cat with a pituitary carcinoma. Neurologic signs improved within 2 months in all 5 cats that presented with abnormal neurologic signs. Clinical signs caused by a concurrent endocrine disorder began to improve within 1-5 months in the 7 cats with hyperadrenocorticism or acromegaly. Radiation therapy is an effective primary treatment modality for cats presenting with neurologic signs associated with a pituitary mass and can improve clinical signs associated with concurrent hyperadrenocorticism or acromegaly in cats with no neurologic abnormalities.