Pleomorphic liposarcoma

Definition

A high grade pleomorphic sarcoma containing pleomorphic lipoblasts.

Epidemiology

Pleomorphic liposarcoma accounts for only about 5% of all liposarcomas and for about 20% of all pleomorphic sarcomas.

Clinical features

This tumour occurs in late adulthood (range 18 to 93, median 63 years). It is often a deep-seated tumour predominantly of the thigh or elsewhere in the limbs girdles(of 63 cases, the most common sites were: lower leg; 23, (including thigh; 18), limb girdles; 11, arms; 10. 45 of 60 were deep-seated, 15 of 60 were subcutaneous). Patients usually present with a mass, but occasionally with dyspnea, fever, SVC obstruction or pleural effusion. Rare subcutaneous cases have been reported.

Macroscopic appearances

Tumours vary form well-demarcated to infiltrating. Most are white to brown-yellow. Occasional cases show myxoid change or necrosis.

Histopathology

Most cases show microscopically infiltrating margins. Diagnosis relies on the identification of lipoblasts: in one third of cases, the lipomatous component is scanty.

Lipoblasts are large with hyperchromatic scalloped nuclei, prominent nucleoli and multivacuolated cytoplasm. The vacuoles appear sharply punched out. There are frequently nuclear pseudoinclusions and multinucleation.

There may be pools of mucin. A lymphoid infiltrate may be present. Eosinophilic hyaline globules may be present. Mitotic rate vary from 103 to 125 per 10 HPF.

Variants:

• High-grade pleomorphic/spindle cell sarcoma with scattered lipoblasts or sheets of lipoblasts

• Epithelioid pleomorphic liposarcoma: cohesive epithelioid cells with variably eosinophilic cytoplasm and distinct cell borders forming a honeycomb pattern. There are round nuclei with prominent nucleoli. Little extracellular matrix is seen but the tumour cells may be separated by thin fibrous septa. There are, at least focally, pleomorphic lipoblasts. About half the case include a spindle cell component2.

• Small round cell variant very similar to round cell liposarcoma.

Immunohistochemistry

Occasional cases show small foci of skeletal muscle differentiation.

Differential diagnosis

• Other types of liposarcoma: myxoid and round cell liposarcomas have a plexiform capillary network, which is lacking from pleomorphic liposarcoma. Dedifferentiated liposarcoma includes areas of clear-cut well-differentiated liposarcoma but does not show large pleomorphic lipoblasts admixed with the non-lipogenic areas.

• Malignant fibrous histiocytoma

• Rhabdomyosarcoma

• Leiomyosarcoma

• Fibrosarcoma

• Haemangiopericytoma

• Acral myxoinflammatory fibroblastic sarcoma (inflammatory myxohyaline tumour)

• MPNST

• Solitary fibrous tumour

• melanoma

• Epithelioid pleomorphic liposarcoma resembles metastatic carcinoma2:

  • renal cell carcinoma: is more uniform, lacks lipoblasts and is more diffusely positive for EMA and cytokeratins, as well as being positive for CD10 and the renal cell carcinoma marker.

  • adrenal cortical carcinoma

Prognosis

Pulmonary metastases are common.

• Five year overall survival is 57%,

• Five year metastasis-free survival is 50%

• Five-year local recurrence-free survival is 48%

Poor prognosis is associated with:

• age greater than 60 years

• a tumour in the torso

• size greater than 5 cm

• more than 20 mitoses per 10 HPF

• tumour necrosis

References

World Health Organization Classification of Tumours, Tumours of Soft Tissues and Bone, IARC Press 2002.

1 Gebhard, S., Coindre, J.M., Michels, J.J., Terrier, P., Bertrand, G., Trassard, M., Taylor, S., Chateau, M.C., Marques, B., Picot, V. and Guillou, L. Pleomorphic liposarcoma: clinicopathologic, immunohistochemical, and follow-up analysis of 63 cases: a study from the French Federation of Cancer Centers Sarcoma Group. Am J Surg Pathol 2002;26:601-16.

2 Miettinen, M. and F. M. Enzinger (1999). "Epithelioid variant of pleomorphic liposarcoma: a study of 12 cases of a distinctive variant of high-grade liposarcoma." Mod Pathol 12(7): 722-8.

3 Evans HL Atypical lipomatous tumor, its variants, and its combined forms: a study of 61 cases, with a minimum follow-up of 10 years. Am J Surg Pathol 2007; 31:1-14

This page last revised 25.5.2007.

©SMUHT/PW Bishop