Tumours composed of fat are no longer a simple diagnosis: an overview of fatty tumours with a spindle cell component

Abstract

This is a review of the morphological spectrum of fatty tumours containing a component of spindle cells, highlighting the immunohistochemical and cytogenetic workup that is now mandatory for accurate diagnosis, with the goal of providing a practical approach for practising surgical pathologists. There have been significant advances in recent years in classifying and understanding the pathogenesis of fatty tumours with spindle cells, based on the correlation of histological, immunohistochemical and cytogenetic/molecular findings. In spite of this, morphological diagnosis and accurate classification of fatty tumours with spindle cells can be challenging to diagnostic pathologists. A group of three lesions: spindle cell lipoma, mammary-type myofibroblastoma and cellular angiofibroma share morphological features and are united by retinoblastoma protein (pRb) loss. Closely allied to these lesions, especially spindle cell lipoma is the newly designated atypical spindle cell lipomatous tumour, which shares morphological, immunohistochemical and cytogenetic features with the trio of tumours lacking nuclear pRb. All of these lesions lack and amplification as well and separation is based on clinical features, principally location. Atypical lipomatous tumour or well-differentiated liposarcoma shows retention of pRb but overexpression and amplification of MDM2. Fatty tumours with spindle cells need to be extensively sampled, with careful attention paid to cellular atypia and location, and they need to have immunohistochemical workup with pRb, MDM2, desmin, CD34 and p16. In addition, cytogenetic analysis for and amplification has become crucial for the proper identification of these lesions.

p16

“…The morphological distinction of well-differentiated liposarcoma or atypical lipomatous tumour from benign fat lesions, especially, deep-seated lipomas can be challenging 10. While there are subtle microscopic clues and location is of paramount importance, sometimes one has to resort to ancillary techniques to resolve a diagnostic dilemma.…”

Dedifferentiated Liposarcoma With Myofibroblastic Differentiation

“…Dedifferentiated liposarcoma typically presents in middleaged and older adults as a large, deep-seated mass. 3,8 The most common site is retroperitoneum, which accounts for approximately half the cases, followed by inguinoscrotal region and thigh. 3 While some DLs are detected incidentally, others are symptomatic owing to obstruction of surrounding structures.…”

“…3 Approximately 90% of DLs present de novo, while the remainder arise within a recurrent WDL. 3,4,8 grade 2 or 3 spindle cell or pleomorphic sarcoma without a specific line of differentiation. Other patterns include tumors with meningothelial-like whorls, metaplastic bone formation, and myxoid stroma; tumors resembling solitary fibrous tumor and inflammatory malignant fibrous histiocytoma; and tumors with prominent epithelioid features.…”

“…Alternatively, MDM2 immunohistochemical stain can demonstrate overexpression at the protein level and is diagnostically useful in some cases. [2][3][4]8 TREATMENT AND PROGNOSIS The 5-year survival rate associated with DL is 20% to 40%. 27,28 The metastatic potential and overall survival associated with DL with myofibroblastic differentiation appears to be similar to that of conventional DL.…”

Liposarcoma — spectrum of disease

“…According to the WHO classification (2013 edition), the following subtypes are distinguished [2]: -lipoma-like: histologically dominated by mature adipose tissue with the presence of septa of connective tissue, visible in magnetic resonance imaging (MR) [5] and -sometimes only single, dispersed -atypical cells, including lipoblasts; -sclerosing: characterised mainly by the growth of fibrous tissue and with a relatively small fat component of the tumour; in this subtype a higher rate of recurrence after resection is observed; -inflammatory, in which chronic inflammatory infiltration is primarily visible; -spindle cell: which is usually characterised by a monomorphic population of spindle cells and often the present myxoid component. Another molecular basis of this subtype is an argument for separating it as a separate disease entity [6,7]. As is clear from the above description, it is a histologically very diverse group of tumours in which both the fatty component and atypical cells, in particular lipoblasts, can be significantly reduced.…”