Liposarcomas are generally large tumors (>10 cm) but can be of almost any size. They occur mainly in adults with only 0.7% of cases occurring in those 5 cm), and painless but highly malignant adipocyte tumors. They occur primarily in individuals >50 years old chest wall,
pelvic cavity,
pulmonary pleurae,
pericardium, and spine. mixed with areas containing undifferentiated cells. The undifferentiated component of these tumors most often consists of spindle-shaped cells, with 25% of cases showing cells with an
epithelioid cell morphology. These tumors have at least some foci with a histopathology similar to high-grade
myxofibrosarcoma type histiocytomas, a tumor formerly termed malignant myxoid fibrous histiocytoma.
Genetics PLS neoplastic cells contain various gene and chromosome abnormalities: the
TP53 gene is
deleted or mutated in 17–60% of cases; the
RB1 gene is deleted in 60% of cases; and the
Neurofibromin 1 gene is lost by inactivating
mutations in 8% of cases or in rarer cases by a deletion around its location in band 11.2 on the long arm of chromosome 12. These cells can also show gains in the genetic material around: bands 12–15 on the short arm of chromosome 5; band 21 on the short arm of chromosome 1; and band 22 on the long arm of chromosome 7. The alterations in gene copy numbers induced by these abnormalities are similar to those seen in the
myxofibrosarcoma type of the histiocytomas. The role(s) of these changes in gene copy numbers in promoting PLS has not been defined. Thus, PLS is unlike other liposarcomas in that its neoplastic cells have a complex genome without characteristic genomic alterations or identifiable genes that drive the disease. Detection of alterations in the expression of the
TP53, RB1, and
neurofibromin 1 genes, as well as other, less commonly altered genes in PLS (e.g.
PIK3CA, tyrosine-protein kinase SYK, PTK2B, EPHA5, and
ERBB4), may help support but do not clearly define a tumor as being PLS.) was first described in a large 2009 study of the liposarcomas. While initially regarded as a possible variant of the myxoid liposarcomas with
pleomorphic features, the
World Health Organization (2020) classified it as a new and distinct form of the liposarcomas. This classification was based on findings that the myxoid pleomorphic liposarcomas, while having histopathological features that were similar to myxoid liposarcomas, had clinical and, most importantly, critical genetic and molecular features that differed from the myxoid as well as the other three liposarcoma forms.
Pathology On histopathologic analyses, MPL tumors consist of areas resembling conventional myxoid liposarcoma; these areas, which represent 30–50% of the total tumor areas, have an abundant myxoid matrix, a well-developed capillary vasculature, bland cells that are round and/or slightly spindle-shaped, vacuolated lipoblasts, and multinucleated cells shaped like small flowers. However, these areas also contain a scattering of highly pleomorphic cells that show greater degrees of nuclear enlargement and irregularity than the cells seen myxoid liposarcoma tumors. Other areas of MPL tumors are more cellular and consist of rapidly growing and highly pleomorphic
lipoblasts. a 2021 review found that there were no consensus recommendations for the standard of care for MPL with respect to radiation and chemotherapy regimens (when used either alone or combined with surgery) for treating these tumors. ==Histopathology of liposarcomas==