Soft tissue sarcoma invasion of the humerus via the nutrient foramen in a dog

A 7-year-old castrated male dachshund dog was presented because of non-weight-bearing right thoracic limb lameness with a soft tissue mass of the proximal humerus. Orthogonal radiographs of the affected limb showed a region of geographic lysis and variable cortical thinning centered in the proximal humeral metaphysis. Differential diagnoses for these lesions included benign and malignant processes, including primary osseous neoplasia. Right forelimb amputation was conducted, and histopathologic assessment facilitated diagnosis of a grade II/intermediate-grade soft tissue sarcoma invading the proximal humerus via the nutrient foramen. No evidence of metastasis was present at the time of surgery. The dog recovered uneventfully following amputation and maintained a good quality of life for 15 mo after surgery. This report describes a unique presentation of a soft tissue sarcoma with osseous invasion, offering an alternative differential diagnosis for monostotic aggressive bone lesions. Key clinical message: This case report describes a unique presentation of a common canine neoplasm. Associated with a more positive prognosis than other primary osseous neoplasms, a soft tissue sarcoma could be considered a differential diagnosis for osseous lesions with soft tissue masses.