Atypical spindle cell lipomatous tumour – A case report

Abstract

The atypical spindle cell lipomatous tumour (ASLT) is a relatively new entity proposed by Mentzel et al. in 2010. The clinicopathological characteristics were further detailed in a large series of 232 cases by Marino-Enriquez et al. in 2017. These lesions presented as a persistent or enlarging mass with a medium size of 5 cm and a wide anatomic distribution. A spectrum of cytological atypia present in these lesions could be alarming. The cellular cases with marked nuclear atypia and frequent lipoblasts could be mistaken as atypical lipomatous tumour/ dedifferentiated liposarcoma. Lack of MDM2 amplification is an important biological characteristic different from its morphology mimic. Despite the concerning histomorphology, none of those 232 patients in the 2017 series developed metastasis or died of disease. The local recurrence rate was 13%. We hereby present such an interesting case in which an 81-year-old male presented with an 8 cm mass at the right shoulder. The cut surfaces of the mass showed fatty tissue with variegated and gelatinous areas. Microscopic examination revealed an admixture of variably sized adipocytes, univacuolated or multivacuolated lipoblasts and spindle cells. Many spindle cells were bland while the remainders were irregular, pleomorphic and hyperchromatic. Multinucleated cells reminiscent of floret giant cells were also present. The stroma was variable ranging from myxoid to collagenous nature. CD34 was diffusely positive among the spindle cells and pleomorphic cells. S100 was positive among the adipocytic cells and negative among the spindle cells. MDM2 and CDK4 immunostains were negative. FISH analysis showed no evidence of MDM2 amplification. The poster will demonstrate the morphological spectra of ASLT and the awareness of this entity will avoid a malignant misdiagnosis.