Non‐resectable extratesticular sustentacular cell tumour treated with palliative‐intent radiation and carboplatin chemotherapy in a dog

There is limited published information regarding the diagnosis and treatment of sustentacular cell neoplasia in dogs, and no data evaluating the use of radiation and chemotherapy for those tumours that are non‐resectable. This case report describes a 5‐year‐old, male, neutered German shepherd dog presented with a large, rapidly growing inguinal mass. Advanced imaging (computed tomography), cytology, histopathology, and immunohistochemistry led to the diagnosis of sustentacular (Sertoli) cell neoplasia. The dog underwent five daily palliative radiation treatments followed by a six‐dose carboplatin chemotherapy protocol. The primary mass was static in size for 7 months following the completion of radiation therapy and 3 months following the conclusion of chemotherapy. Progressive (presumed) metastatic lymphadenopathy was observed 1 month after discontinuing carboplatin chemotherapy. The combination of therapies utilised in this case appears to have provided temporary clinical benefit; however, further research is needed to determine the best treatment recommendations for non‐resectable sustentacular cell tumours.