Lesions restricted to cutis only rarely metastasize


• Perpendicularly oriented fascicles of spindle cells

• Brightly eosinophilic cytoplasm

• Blunt-ended nuclei

• Nuclear atypia and mitoses

Ancillary Tests

• Labels as per smooth muscle: Desmin, actin, calponin, caldesmon
image Some cases stain with keratins

Top Differential Diagnoses

• Sarcomatoid squamous cell carcinoma

• Atypical fibroxanthoma

• Leiomyoma

• Dermatofibroma/fibrous histiocytoma

• Nodular fasciitis

• Inflammatory myofibroblastic tumor

Cutaneous Leiomyosarcoma (Atypical Smooth Muscle Tumor)
Based on the lack of involvement of the subcutaneous adipose tissue, a favorable prognosis would be anticipated for this lesion. In fact, some observers have suggested diagnosing such superficial cutaneous lesions as atypical smooth muscle tumors.

Superficial Area of Cutaneous Leiomyosarcoma
This leiomyosarcoma (LMS) extended into the subcutis. It is composed of perpendicularly oriented fascicles of brightly eosinophilic cells. Even at scanning magnification, atypical nuclei stand out image.

Leiomyosarcoma at High Magnification
Mitotic figures are usually easily found in LMS. There is no need to search for numerous mitoses, although mitotic counts assist in assigning a sarcoma grade. Note the bright pink color of the tumor cells’ cytoplasm.

Leiomyosarcoma With Anaphase Bridge
LMSs do not show a characteristic translocation and have chromosome instability, as indicated by the presence of anaphase bridges image, long cords of chromatin that remain as cells separate in anaphase. Note the blunt-ended nuclei image.



• Leiomyosarcoma (LMS)


• Malignant neoplasm composed of cells exhibiting smooth muscle differentiation


Infectious Agents

• Epstein-Barr virus (EBV) smooth muscle tumors (SMT) in immunosuppressed patients

• Occasional examples are radiation associated



• Incidence
image Uncommon: 10-15% of extremity sarcomas

image Most common overall sarcoma type if uterine and visceral examples are included

• Age
image Middle-aged adults

• Sex
image No gender preference overall


• Cutaneous LMS presents as single nodule or plaque-like tumor
image May be ulcerated or show serum crusting/hemorrhage

• Deep soft tissue tumors present as mass, often asymptomatic, in extremities
image Retroperitoneum most common site

image Vena cava examples often symptomatic

• Uterine examples considered separately with unique diagnostic criteria


• Surgical excision
image Radiation

image Chemotherapy for metastatic tumors


• Outcome site and stage dependent as with other sarcoma types
image Lesions restricted to cutis only rarely metastasize

– Some observers have advocated diagnosing them as atypical SMTs

image Subcutaneous lesions

– Up to 40% of tumors metastasize

– Over 30% of patients with subcutaneous tumors die of disease

image Retroperitoneum: About 80% of patients die of disease, typically with metastases

image Bone: Metastases in up to 1/2 of patients

image Vena cava: 5- and 10-yr survival 50% and 30%, respectively

image Head and neck: Over 1/2 metastasize


Histologic Features

• Perpendicularly oriented fascicles of spindle cells

• Cells show brightly eosinophilic cytoplasm

• Blunt-ended nuclei with nuclear atypia

• Some examples are epithelioid-appearing

• Any number of mitoses sufficient in subcutis, scrotal lesions, or deep soft tissue if nuclear atypia is present

• In vulva, some observers offered > 5 mitosis per 10 HPF as cutoff, but recurrences reported in lesions with any mitotic activity

Predominant Pattern/Injury Type

• Fascicular

Predominant Cell/Compartment Type

• Mesenchymal, smooth muscle

Variant and Special Forms

• Epithelioid leiomyosarcoma
image Literature confounded because many epithelioid gastrointestinal stromal tumors (GIST) were termed epithelioid LMS in past

image Found anywhere in body

image Distinct epithelioid morphology, but more nuclear atypia than GISTs

image Older studies reported smooth muscle actin (SMA) and muscle specific actin (MSA)-positive, desmin-negative immunophenotype, but desmin labels most lesions using modern methods

– Possible reflection of misdiagnosed GISTs

– Less sensitive desmin antibodies used in past

• Myxoid leiomyosarcoma
image Grossly gelatinous

image Extensive myxoid change, but zones of typical leiomyosarcoma allow for diagnosis
– Express desmin and actin

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Apr 24, 2017 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Leiomyosarcoma

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