Introduction

• Soft tissue sarcoma are tumors arising from mesenchymal connective tissues. They are usually grouped together as they generally behave in a similar manner. The benign mesenchymal tumors, eg fibroma, are quite rare, locally expansile tumors that are cured by local surgical excision. These tumors by definition do not metastasize and they generally only cause clinical problems by their size or location. The malignant counterparts are generally referred to as ‘soft tissue sarcomas’ (STS) as they mostly present, behave, and are treated, in a similar manner.
• STS account for 15-20% of all canine tumors: although incidence can vary according to breed - see below.
• Signs: firm, fibrous mass affecting skin/subcutis, may be adherent to underlying tissue, slow growing.
• Include:
  • Fibrosarcoma Fibrosarcoma.
  • Spindle cell sarcoma.
  • Peripheral nerve sheath tumor Nerve sheath: neoplasia.
• Diagnosis: biopsy and histopathology.
• Treatment: surgical resection +/- radiotherapy.
• Prognosis: based on histological grade, mitotic index and evaluation of margins.

Pathogenesis

Etiology

• Largely unknown in dog.
• Occasionally associated with chronic inflammation.
• Rarely arise at sites of burns or implants.
• Rarely radiation induced.

Classification

• According to presumed tissue of origin based on histological appearance of neoplastic cells and stroma:
  • Fibrosarcoma - fibrous connective tissue (when evidence of collagen formation is lacking, often referred to as ‘spindle cell sarcoma’).
  • Peripheral nerve sheath tumor (PNST) Nerve sheath: neoplasia.
  • Liposarcoma - adipose tissue.
  • Leiomyosarcoma - smooth muscle Leiomyoma  /Leiomyosarcoma.
  • Rhabdomyosarcoma - skeletal muscle.
  • Myxosaroma - myxoid stroma.
  • (Hemangiopericytoma Hemangiopericytoma - most now reclassified as PNST).

• Some poorly differentiated tumors which lack cellular / stromal features to indicate tissue of origin may be referred to as ‘poorly differentiated’ or ‘anaplastic’ sarcoma.
• The following may also be described as soft tissue sarcoma, but are ‘excluded’ from the following general description / management because their biological behavior is more aggressive:
  • Synovial (cell) sarcoma Synovial cell sarcoma.
  • Histiocytic sarcoma - dendritic cell origin Malignant histocytosis.
  • Hemangiosarcoma - vascular endothelium Hemangiosarcoma.
  • Osteosarcoma - bone Osteosarcoma.

Timecourse

• Relatively slow growing.

Diagnosis

Treatment

Outcomes