Introduction

The objective of this study was to describe the histopathological and immunohistochemical (IHC) characteristics of non-visceral leiomyosarcoma in dogs.

Methods

A retrospective case series was performed of 22 client-owned dogs. Medical records were reviewed to identify dogs originally diagnosed with non-visceral leiomyosarcoma. Histologic and clinical details were obtained. Biopsy samples were reviewed by a single pathologist using standardized histologic criteria including appearance and IHC labeling (positive smooth muscle actin (SMA) and desmin or positive SMA and laminin).

Results

Twenty-two possible non-visceral leiomyosarcomas were identified. Most dogs were middle aged (median 8.6 years, range 0.9 to 14.6) with variably located subcutaneous and cutaneous masses. Of the 22 cases, only four were consistent with a definitive diagnosis of non-visceral leiomyoma (1) or leiomyosarcoma (3) based on the established criteria. Of these, only the leiomyoma had diffuse immunoreactivity against all three markers, while all three leiomyosarcomas had diffuse SMA and near diffuse laminin staining. Eleven additional samples had moderately consistent histologic features but variable immunoreactivity, and a definitive diagnosis could not be determined.

Interestingly, five samples were reconsidered as benign soft tissue lesions. Two samples were reclassified as fibrosarcoma.

Conclusion

These data highlight the uncommon nature of non-visceral leiomyosarcoma and the importance of immunohistochemical analysis for diagnosis of sarcoma subtypes. SMA is a common single IHC used for the diagnosis of leiomyosarcoma, but standardized IHC profiles are lacking for classification of smooth muscle tumors. Further research is required to clarify the histologic and immunohistologic features and the clinical significance of non-visceral SMA positive spindle tumors.

Funding Information

Center for Companion Animal Health, UC Davis School of Veterinary Medicine resident grant