A 10-year-old neutered Spoodle referred for radiation therapy of subcutaneous mast cell tumour.

Owners first noted limping on 12/9/2018. A small inguinal nodule was observed concurrently. This progressed to more marked swelling in the left inguinal region prompting evaluation at the family veterinarian on 25/9/2018 with an aspirate being consistent with mast cell tumour. The patient was referred to a local speciality hospital for workup.

A CT done on 29/9/18 showed a well-defined heterogeneous soft tissue attenuating contrast enhancing 4.7cm lesion associated with the left inguinal region, and an additional prominent 1.6 by 0.8cm inguinal lymph node. No thoracic or abdominal disease was reported.

Given the extent of the tumour and degree of local tissue invasion a penile amputation and urethrostomy was discussed. The patient was referred to the oncology team to discuss stereotactic radiation therapy as an alternative. On presentation the swelling had progressed, and the patient was significantly more painful. A planning CT scan was done on 8/10/2018 and treatment started the following day.

After 2 doses the tumour had decreased notably in size. 3 weeks post treatment there was mild acute moist desquamation of the skin in the treatment field which healed well over the next 2 weeks. The patient was considered to be in clinical remission by one month post treatment. Alopecia and variable dermal pigmentation persisted in the tissues. A course of vinblastine chemotherapy was subsequently initiated at the local referral hospital. The patient has since been lost to follow