Radioactive holmium microspheres for the treatment of soft tissue sarcoma in dogs and cats

Abstract

Twelve client-owned veterinary patients (8 dogs, 4 cats) with unresectable soft tissue sarcoma of different histologic types were treated with intratumoral injections consisting of radioactive holmium microspheres. Nine out of twelve animals underwent subsequent surgery. Tumor response and toxicity were evaluated retrospectively. Overall, holmium treatment was well tolerated with minor side effects. The tumor-absorbed dose varied between 34-5767 Gy and there was no obvious dose-response relation observed. Interestingly, the higher radiation doses were not associated with increased toxicity. Complete response, being >50% tumor volume reduction after holmium treatment allowing for subsequent surgery, was observed in 5 animals. Four animals had partial response, being a tumor volume reduction of 20-50%. Progressive disease, being ≤20% tumor volume reduction, was seen in two cases. Complete remission after having had subsequent surgery was achieved in six animals. Median survival time for all treated patients was 457 days (range 93–1772 days). Six animals were alive at the time of writing, five died and one was lost to follow-up. Two out of five animals died owing to tumor recurrence. Intratumoral insertion of radioactive holmium microspheres appeared to be a safe and effective modality for the downstaging of selected cases of unresectable soft tissue sarcomas allowing for subsequent surgery.