Presurgical Pulmonary Imaging in Dogs with Soft Tissue Sarcoma

In the Literature

Villedieu EJ, Petite AF, Godolphin JD, Bacon NJ. Prevalence of pulmonary nodules suggestive of metastasis at presentation in dogs with cutaneous or subcutaneous soft tissue sarcoma. J Am Vet Med Assoc. 2021;258(2):179-185.

The Research …

Nonvisceral soft tissue sarcomas (STSs) are often cured with aggressive local control (ie, surgery and/or radiation therapy). Tumor grade is the most important predictor for biological behavior and metastatic potential. Previously reported rates of metastasis range from 0% to 41%,¹ and the rate of metastasis to the lungs increases with increased tumor grade. Staging is a standard and integral diagnostic step that should be performed before aggressive local control is applied. Standard staging should include thoracic imaging and can be performed with either CT or 3-view survey radiography of the thorax. CT is considered more sensitive than radiography and may detect lesions as small as 1 to 2 mm.^2-4 Both procedures are considered low-risk, and discussion with pet owners should focus on the diagnostic value of each test before definitive therapy is started. 

The goals of this study were to investigate the prevalence of pulmonary nodules suggestive of metastasis in dogs (n = 146) with cutaneous or subcutaneous STS using either thoracic radiography or CT and to identify possible associations between prevalence and patient and tumor characteristics. This study only included patients with no previous thoracic imaging to reduce bias. Patients with visceral or more biologically aggressive sarcomas and those with no final histologic diagnosis of STS were excluded from the study.  

Results showed that the presence of pulmonary lesions suggestive of metastasis increased with tumor grade. Overall, nodules suggestive of metastasis were present in only 11.7% of dogs. Nodules consistent with metastatic disease were reported as grade 1 (6%), grade 2 (6%), and grade 3 (38%). These findings are comparable to the historically reported metastasis rate for STS in dogs. 

STS duration before presentation (>3 months vs <3 months) was a useful predictor of metastatic disease at diagnosis. Although the authors concluded that thoracic imaging is a low-yield test, it can detect pulmonary metastases and define other potential underlying thoracic abnormalities. Sarcoma tumor grade is typically determined after removal, rather than before surgery. 

In this author's opinion, thoracic imaging should be performed before definitive therapy in all cases of STS. CT may be reserved for lesions that have been present >3 months.

… The Takeaways

Key pearls to put into practice:

• Staging with thoracic imaging is an important part of oncologic decision-making and may help to identify other underlying disease processes.

• Tumor grade is the most important factor in determining the metastatic potential of nonvisceral STS.

• Patients with nonvisceral STS present for >3 months are more likely to have metastatic disease. Thoracic CT may be reserved for large, rapidly growing, invasive lesions that have been present >3 months; thoracic radiography may be sufficient for screening in most cases of STS.