Strontium 90 plesiotherapy for the treatment of eyelid squamous cell carcinoma in eight cats

Squamous cell carcinoma (SCC) is the most common eyelid tumour in cats. The main treatment is extensive surgery and the cosmetic outcome can be worrisome for some owners. Strontium 90 (ST-90) plesiotherapy is a therapeutic modality used for superficial tumours, including SCC. The aim of this study was to describe the use and response of feline eyelid SCC to ST-90 plesiotherapy either as single treatment or as adjuvant therapy following surgery.

A referral centre clinical database was searched for all cats diagnosed with SCC located on an eyelid. Cats treated with ST-90 plesiotherapy were included. The response to treatment was evaluated visually every 4-6 weeks until complete healing and based on response evaluation criteria in solid tumours (RECIST). Descriptive statistics of the survival were applied to the data collected.

Eight cats treated between 2014 and 2017 met the inclusion criteria. The median age was 10.8 years. In six cases, ST-90 was used as the only treatment modality, while in two cats it was used as an adjuvant to surgery. Four cats received a single protocol and four a hypofractionated protocol. In the six cats in which ST-90 was used as the primary treatment, the response was 100%. Four cats died at a median time of 9 months (3-17 months) after ST-90 due to causes unrelated to SCC. Of the remaining four cats, three had no signs of recurrence at a median time of 34 months and one was lost to follow-up at 17 months with no signs of recurrence.

This small study showed that ST-90 can be used for treatment of eyelid SCC with good therapeutic and cosmetic outcomes.