Liposarcoma

Liposarcoma most common sites

·    Deep soft tissues of proximal extremities

·    Retroperitoneum

Myxoid Liposarcoma

Histology, immunohistochemistry , and cytogenetic features

·    Light microscopy

o    Nodular growth pattern on low power

o    Enhanced cellularity at the periphery of the lobules

o    Mixture of uniform round to oval shaped primitive non lipogenic mesenchymal cells and small signet ring lipoblasts in a prominent myxoid stroma

o    Delicate arborising, “chicken-wire” vasculature

o    Extracellular mucin forms large pools creating a microcystic, lymphangioma-like/”pulmonary edema” growth pattern

o    Lack of nuclear pleomorphism, giant tumour cells, prominent areas of spindling, or significant mitotic activity

o    Subset of myxoid liposarcoma shows histologic progression to hypercelllular or round cell morphology (significantly poorer prognosis)

Characterized by solid sheetes of back-to-backl primitive round cells with high N:C ratio and conspicuous nucleoli with no intervening myxoid stroma

   May be composed of close-packed relatively small cells similar to those in the myxoid areas or may less often cosist of larger rounded cells with variable amounts of eosinophilic cytoplasm

Immunohistochemistry

o    Diffuse staining for S-100

Cytogenetics

o    t(12;16)(q13;p11) present in >90% of cases

o    Leads to fusion of DDIT3 (CHOP) and FUS (TLS) genes and the generation of a FUS/DDIT3 hybrid protein

o    In rare cases, a t(12;22)(q13;q12) oocurs where DDIT3 fuses with EWS

Liposarcoma prognosis

·    Well differentiated / Atypical lipomatous tumor

o    Most important prognostic factor is anatomic location

o    Tumours occurring in deep anatomic sites such as retroperitoneum, spermatic cord, or mediastinum tend to recur repeatedly

o    May cause patient’s death due to uncontrolled local effects, dedifferentiation, or metastasis

o    Mortality ranges from 0% for atypical lipomatous tumour of peripheral extremities to >80% for WDL in retroperitoneum if patients are followed for 10-20 years

Myxoid liposarcoma

o    High histologic grade defined as 5% or more areas of round-cell morphology, necrosis and TP53 expression

o    Clinical outcome is poor regardless of low grade appearance

o    Prone to recur locally and one-third develop distant metastasis

o    80% survival at 100 months (localized)

o    20% survival at 100 months (high-grade)

Pleomorphic liposarcoma

o    Tumour depth and size, 20 or more mitotic figures/10HPF, and necrosis associated with worse clinical prognosis

o    Aggressive neoplasm

o    30-50% metastatic rate

o    Overall tumour associated mortality of 40-50%

o    Many patients die within a short period of time

Dedifferentiated liposarcoma

o    Recurs locally in 40% of cases

o    Almost all recur locally if patient followed for 10-20 years

o    Distant metastases in 15-20% of cases with overall mortality of 30% at 5 years followup

o    Most important prognostic factor is anatomic location with retroperitoneal lesions exhibiting worst clinical behaviour