Lipomatous tumours of soft tissues: an update

This review summarizes the clinicopathological features of recently characterized variants of lipomatous tumours of soft tissue, attempts to deal with some difficult conceptual issues relating to adipocytic neoplasms and aims to provide an update on cytogenetic aspects of fatty tumours. Myolipoma is a rare benign neoplasm, occurring most frequently in adults in the deep soft tissue of the abdomen or retroperitoneum, and is composed of irregularly admixed mature adipose and smooth muscle tissues. Chondroid lipoma represents an unusual benign lesion occurring mainly in adult females subcutaneously or in deep soft tissue; it is easily mistaken for myxoid liposarcoma or extraskeletal myxoid chondrosarcoma. Spindle-cell liposarcoma is a variant of well-differentiated liposarcoma quite commonly found in subcutaneous tissue of the shoulder region and upper limbs and is composed of relatively bland-appearing spindle cells mixed with a well-differentiated liposarcomatous component. Recently there has been considerable debate about classification of lipomatous tumours. The term atypical lipoma was proposed for a group of well-differentiated non-metastasizing liposarcomas arising in surgically amenable soft tissues and for deep-seated atypical adipocytic neoplasms that show variation in adipocytic size and atypical stromal cells but lack lipoblasts. However, these neoplasms recur repeatedly and may dedifferentiate and thereby acquire metastatic potential. We use the diagnosis atypical lipoma with caution and propose to use the terms well-differentiated liposarcoma and atypical lipoma interchangeably. The relationship between myxoid and round-cell liposarcoma, which constitutes the morphological spectrum of a single entity, has been clarified but there remain considerable problems in defining likely clinical behaviour. The recent advances in cytogenetic characterization and classification of lipomatous tumours, which is already proving to be of diagnostic importance, are reviewed, and the genetic importance of the distinct chromosomal translocation in myxoid/round cell liposarcoma is briefly discussed.