Pathology of Leiomyosarcoma

(Skin and Soft Tissue)

Dr Sampurna Roy MD                           2022

1. Cutaneous (primary or secondary); 

2. Subcutaneous and deep soft tissue; 

3. Intra-abdominal 

4. Vascular.

Leiomyosarcoma commonly occurs in the fifth to seventh decade. Cutaneous variant usually occurs in younger adults.

1. Cutaneous leiomyosarcomas are commonly located on the extensor surfaces of the extremities, particularly lower legs.

Rarely these may occur on the scalp, upper lips, nipple and scrotum.

Grossly the tumour is usully less than 2 cm in diameter.

External surface may display areas of discolouration, umbilication and ulceration.

Cut surface reveals a grayish white whorled appearance. Local recurrences may occur. 

There is usually no evidence of metastasis.

Secondary leiomyosarcomas arise from primary retroperitoneal or uterine leiomyosarcoma and present as dermal and subcutaneous nodules on the scalp or back.  

2. Subcutaneous leiomyosarcoma are commonly located on the thigh. 

These are larger lesions and grow rapidly.

Recurrence occurs in 50%-70% cases.

Distant metastasis to lung, liver and bone occur in about 50% cases.

3. Intra-abdominal leiomyosarcomas are located in the retroperitoneum, mesentery and omentum.

These are large lesions and often unresectable.

The mean size of the tumour  is about 16 cm.

The tumour presents as a fleshy gray white mass with foci of hemorrhage and necrosis.

Cystic degeneration may be present.

Some tumours macroscopically resemble leiomyoma on cut sections.

4. Vascular leiomyosarcoma occur in large veins.

( Inferior vena cava or larger veins of leg - saphenous, iliac and femoral).

Macroscopically nodular or polypoid masses are firmly attached to the vessel.

The tumour spreads along the surface of the blood vessel.

 

Pathological features:

The tumour is composed of interlacing fascicles of spindle cells with eosinophilic cytoplasm and blunt ended nuclei (cigar shaped).

The appearance of the tumour varies according to the degree of differentiation.

Dermal leiomyosarcoma demonstrates an irregular outline.

The tumour cells blend into surrounding collagenous stroma.

A superficial grenz zone may be present.

The tumour is usually located in the dermis but may extend into the subcutis.

The overlying epidermis shows some flattening of the rete ridges.

Subcutaneous leiomyosarcoma may extend into the lower dermis. A prominent vascular pattern is evident.

Variants:

Leiomyosarcoma with osteoclast giant cells-

Pleomorphic leiomyosarcoma- 

There is marked pleomorphism with 'MFH' - like areas , extensive hyalinization and numerous osteoclastic giant cells.

Inflammatory leiomyosarcoma- There are small lymphoid aggregates.

These tumours are known to have better prognosis.

Granular cell leiomyosarcoma- Intracytoplasmic eosinophilic granules are present.

Epithelioid leiomyosarcoma- There are epithelioid cells. These may be mistaken for melanoma.

Desmoplastic leiomyosarcoma-  Stromal sclerosis is present.

Myxoid leiomyosarcoma-  Rarely occur in deep soft tissue.

Grossly  may be gelatinous in appearance. Microscopically characterized by extensive myxoid areas.

The spindle cells are separated by pools of  hyaluronic acid

In areas tumour cells are arranged in cord- like pattern reminiscent of myxoid chondrosarcoma.

Mitotic rate is low.

The tumour is not as aggressive as previously suggested.

Immunohistochemistry may be necessary for distinction from a nerve sheath tumour.

Histochemistry:

Well differentiated cells demonstrate myofibrils with Masson Trichrome stain as deep red longitudinal  parallel lines.

PAS positive intracytoplasmic glycogen is present.

Reticulin stain show a fine reticulin network between muscle fibres.
 

Immunohistochemistry: 

There is smooth muscle actin positivity in the cytoplasm.

Desmin is positive (often focal) in 70% cases and is usually absent in high grade tumours. 

Pan-muscle actin (HHF-35) is usually positive.

Cytokeratin and S100 protein positivity is noted in 30 - 40% cases.

Differential expression of smooth muscle myosin, smooth muscle actin, h-caldesmon, and calponin in the diagnosis of myofibroblastic and smooth muscle lesions of skin and soft tissue.

Leiomyosarcoma of scrotum--case report and review of literature.

A case of primary hepatic leiomyosarcoma presenting with multiple subcutaneous scalp mass.

A giant subcutaneous leiomyosarcoma arising in the inguinal region.

Pleomorphic leiomyosarcoma: clinicopathologic and immunohistochemical study with special emphasis on its distinction from ordinary leiomyosarcoma and malignant fibrous histiocytoma.

Myxoid leiomyosarcoma of soft tissue, an underrecognized variant.

Leiomyosarcoma of soft tissue in children: clinicopathologic analysis of 20 cases.

Leiomyosarcoma with prominent osteoclast-like giant cells. Analysis of eight cases closely mimicking the so-called giant cell variant of malignant fibrous histiocytoma.