Desmin‐positivity in spindle cells: Under‐recognized immunophenotype of lipoblastoma

Abstract

Lipoblastoma is a distinct benign fatty tumor composed of adipocytes, lipoblasts, and primitive mesenchymal cells with a myxoid stroma. Lipoblastoma harbors characteristic fusion genes involving the PLAG1, resulting in aberrant expression of PLAG1. However, the nature of the primitive mesenchymal cells remains obscure. In our routine pathology practice, we noticed desmin-positive spindle mesenchymal cells in lipoblastomas, which is a hitherto poorly described phenomenon. Thus, we examined the expression of several myogenic markers including desmin in a variety of 95 mesenchymal tumors with fatty elements. Fourteen of the 15 lipoblastomas examined contained desmin-positive spindle cells, which also showed nuclear expression of PLAG1, whereas α-smooth muscle actin, muscle specific actin, h-caldesmon, and myogenin were negative. Some spindle cells in subsets of atypical lipomatous tumors/well differentiated liposarcomas (6/20), dedifferentiated liposarcomas (11/31) and pleomorphic liposarcomas (2/10) were positive for actins and/or desmin, supporting focal myofibroblastic or smooth muscle differentiation. The other tumors, including 11 myxoid/round cell liposarcomas, four spindle cell lipomas, and four lipofibromatoses, were negative for all of the myogenic markers assessed. The almost consistent desmin expression in spindle mesenchymal cells suggests a potential diagnostic utility of this marker and myofibroblastic phenotype of fractions in lipoblastoma cells.

Immunoreactivity of Canine Liposarcoma to Muscle and Brown Adipose Antigens

“…Desmin and α-SMA were selected in this study because they are the most commonly reported muscle markers to be immunoreactive to liposarcoma in pleomorphic liposarcomas in humans. 14 Our results indicate that this is also true in canine liposarcoma as desmin and α-SMA actin were the most commonly expressed muscle markers in this study. Desmin is frequently considered a muscle-specific antigen, but recent research has revealed its relatively low specificity.…”

“…Markers of muscle differentiation are reportedly expressed in some spindle cells in certain subtypes of human liposarcomas, including well-differentiated, dedifferentiated, and pleomorphic subtypes. 14 A recent review of liposarcoma in domestic animals stated that pleomorphic liposarcomas are uniformly negative for these markers. 8 In contrast, another recent article reported that 2 poorly differentiated canine liposarcomas were immunoreactive to a muscle marker (ie, desmin), but these poorly differentiated tumors were not confirmed to be liposarcoma with lipid stains.…”

Submucosal Colonic Lipoblastoma Presenting With Colo-colonic Intussusception in an Infant

“…Myxoid change can be observed in fat lobules, but these lack immature adipocytes or desmin positive mesenchymal elements characteristic of lipoblastoma. [2][3][4]13 Myxoid liposarcoma is invasive both grossly and on microscopic examination; our case was neither. Also, myxoid liposarcoma generally shows a more irregular architecture with less distinct nodules.…”

“…While we were unable to demonstrate an underlying alteration of chromosome 8q11.2 for technical reasons and thereby confirm the diagnosis of lipoblastoma, the latter is strongly supported by the observed extensive immunostaining of mesenchymal cells in lobules and septa for desmin. The diagnostic utility of desmin staining in distinguishing lipoblastoma from potential mimics was first highlighted in a series presented by Saad et al 2 and subsequently confirmed by Kubota et al 3 In the 2 series, 23 out of 24 lipoblastomas showed extensive desmin immunostaining of spindle cells in septa, and depending on the degree of differentiation, also in lobules. Lipoma and lipofibromatosis/lipofibroma on the other hand were consistently negative for desmin as was normal adipose tissue from fetuses and infants.…”

“…Staining of spindle cells for desmin provides an additional diagnostic clue. 2,3 In most cases, lipoblastoma involves soft tissues of extremities and the trunk and presents as a slowly growing circumscribed lesion or mass. Other less common locations include the head and neck area, mediastinum, lung, inguinal/scrotal area, retroperitoneum, mesentery, and omentum.…”