Pleomorphicliposarcomaconsistsofsheetsofanaplasticcells,bizarrenuclei,andvariableamountsofimmatureadipocytes(lipoblasts).Thesetumorshavecomplexkaryotypes.
All types of liposarcoma recur locally and often repeatedly unless adequately excised. The well-differentiated variant is relatively indolent, the myxoid/round cell type is intermediate in its malignant behavior, whereas the pleomorphic variant usually is aggressive and frequently metastasizes.
Nodular fasciitis is a self-limited fibroblastic and myofibroblastic proliferation that typically occurs the upper extremities of young adults. A history of trauma is present in approximately 25% to 50% of cases, and the tumors grow rapidly during a period of several weeks or months. Whereas nodular fasciitis was historically considered a purely reactive lesion, identification of a t(17;22) translocation producing a MYH9-USP6 fusion gene indicates that it is a clonal, yet self-limited, proliferation. It is hypothesized that the proliferating cells lack some key hallmark of cancer, perhaps the ability to avoid senescence. Intriguingly, ABC (discussed earlier), another tumor that sits in a gray zone between reactive and neoplastic proliferations, also contains a USP6 fusion gene. Nodular fasciitis can spontaneously regress and, if excised, rarely recurs. Malignant transformation is virtually nonexistent.
MORPHOLOGYNodularfasciitisarisesinthedeepdermis,subcutis,fascia,ormuscle.Grosslythelesionislessthan5cm,circumscribed,orslightlyinfiltrative.Itishighlycellularcontainingplump,immatureappearingfibroblastsandmyofibroblastsarrangedinapatternreminiscentofculturedfibroblasts(
Fig.21.46 ).Agradientofmaturation(zonation) fromcellular,loose,andmyxoidtoorganizedandfibrousistypical.Thecellsvaryinsizeandshape(spindletostellate)andhaveconspicuousnucleoli;mitoticfiguresareabundant.Lymphocytesandextravasatedredbloodcellsarecommonbutneutrophilsareunusual.
Superficial fibromatosis is an infiltrative proliferation that can cause local deformity but has an innocuous clinical course. All forms of superficial fibromatosis affect males more frequently than females. They are characterized by nodular or poorly defined broad fascicles of fibroblasts in long, sweeping fascicles, surrounded by abundant dense collagen. Several clinical subtypes have been identified:
Palmar (Dupuytren contracture). Irregular or nodular thickening of the palmar fascia either unilaterally or bilaterally.
Plantar. Common in young patients, unilateral and without contractures.
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Fig.21.45Liposarcoma.(A)Thewell-differentiatedsubtypeconsistsofmatureadipocytesandscatteredspindlecellswithhyperchromaticnuclei.(B)Myxoidliposarcomawithabundantgroundsubstanceandarichcapillarynetworkinwhichtherearescatteredimmatureadipocytesandmoreprimitiveround-tostellatecells.
• Penile (Peyronie disease). Palpable induration or mass on the dorsolateral aspect of the penis.
In about 20% to 25% of cases, the palmar and plantar fibromatoses stabilize and do not progress, in some instances resolving spontaneously. Some recur after excision, particularly the plantar variant.