Coarse Fractionated Radiation Therapy for Pituitary Tumours in Cats: A Retrospective Study of 10 Cases

Introduction:  Pituitary tumours are uncommon in cats. Signs may be due to either an expansile mass or paraneoplastic effects (acromegaly and/or unstable diabetes mellitus). There are a few small case series providing evidence of efficacy for radiotherapy of pituitary tumours in cats. This retrospective study describes the outcome of ten cats with pituitary tumours treated with course‐fractionated radiation.
Methods:  The medical records of cats with MRI‐confirmed pituitary tumours that underwent radiotherapy were reviewed. A standard coarse‐fractioned radiation protocol was used; 37 Gy in 5 once‐weekly fractions using two parallel‐opposed 4MeV X‐ray beams. Survival times were calculated from date of first radiation dose.
Results:  Ten cats with pituitary tumours underwent radiotherapy. 5 cats had CNS signs and 5 had evidence of growth hormone excess (1 cat also showed CNS signs). 2 cats with pre‐existing moderate to severe CNS signs died of unknown causes before completing the radiation course. Of the remaining 4 with CNS signs, 3 had complete resolution of signs and the fourth showed partial improvement. Of the 5 cats with unstable diabetes, 2 no longer required insulin and 3 became stable at a lowered dose. The median survival time was 77.6 weeks. 6 cats died: 2 without completing the radiation course, 2 from unrelated causes (CRF, VAFS) and 2 from relapse and/or progression of CNS signs. 4 cats remain alive (range 34–191 weeks).
Conclusions:  Radiation therapy is confirmed as an effective treatment for pituitary tumours in cats giving extended survival and control of both direct mass effect and paraneoplastic signs.