Immunoreactivity of Canine Liposarcoma to Muscle and Brown Adipose Antigens

Abstract

Liposarcoma, rhabdomyosarcoma, and hibernoma share some overlapping histologic and immunohistochemical features. Although immunohistochemistry (IHC) is commonly used in the diagnosis of these neoplasms, expression of muscle markers has been reported in human liposarcoma and canine hibernoma in addition to rhabdomyosarcoma. Thus, these neoplasms are a diagnostic challenge but important to distinguish because of differences in prognosis and treatment. Rhabdomyosarcoma and liposarcoma are both malignant, but rhabdomyosarcoma has a higher potential for metastasis. In contrast, hibernomas are benign with low risk of recurrence. This study investigated expression of the muscle markers desmin, myogenin, and α-smooth muscle actin (α-SMA) and the brown fat marker uncoupling protein 1 (UCP1) in 25 cases of canine liposarcoma using IHC. Oil red O histochemistry was performed to confirm the presence of lipid and the diagnosis of liposarcoma in cases that were not well-differentiated. The 25 cases included 15 well-differentiated, 5 pleomorphic, 3 myxoid, and 2 dedifferentiated subtypes of liposarcoma. By IHC, 23 of 25 expressed UCP1, 7 of 25 expressed α-SMA, 7 of 25 expressed desmin, and 3 of 25 expressed myogenin with no clear relationship of antigen expression and tumor subtype. These findings clarify the immunohistochemical profile of canine liposarcoma and suggest overlap in the expression of several muscle antigens and UCP1 between liposarcoma, hibernoma, and rhabdomyosarcoma.

Immunophenotypic expression of UCP1 in hibernoma and other adipose/non adipose soft tissue tumours

“…Absence of UCP1 staining in most adipose tumours would also indicate that ‘browning’ of WAT to form beige/brite cells is not seen to any great extent. Our results contrast with the findings of La Doucer et al [18], who noted not only that canine well-differentiated liposarcomas express UCP1 but also that a number of such tumours express smooth muscle actin and desmin with one case expressing myogenin; in our experience, these antigens are rarely expressed in well-differentiated or other subtypes of liposarcoma.…”

“…UCP1 is highly expressed in hibernoma, a tumour containing abundant BAT cells [14–17]. There are a few reports of UCP1 expression by tumour cells in liposarcoma [18, 19], but immunophenotypic expression of UCP1 in malignant adipose tumours has not been characterised. In this study, we have sought to determine whether UCP1 is expressed in specific benign and malignant adipose tumour subtypes.…”

Cytologic appearance of hibernoma in two dogs

“…Immunohistochemistry for uncoupling protein 1 (UCP1), also known as thermogenin, has been used to suggest brown adipose tissue origin in humans, rodents, and dogs 1,8,16 . However, the immunoreactivity to UCP1 has also been described in canine liposarcomas 17 . Therefore, the diagnosis of hibernoma should be made not only with UCP1 immunoreactivity but also with compatible clinical and histologic features.…”

What is your diagnosis? Subcutaneous mass in a dog

“…Multiple studies have examined the immunohistochemical characteristics of liposarcomas. Liposarcomas have been documented as cytokeratin negative and vimentin positive with variable α‐smooth muscle actin, desmin, myogenin, and uncoupling protein 1 (UCP1) labeling . An immunohistochemical panel for the definitive diagnosis of liposarcomas has not described in dogs.…”