Epithelioid Smooth Muscle Tumors of the Uterus

 

Features of epithelioid smooth muscle tumors:

(1) predominantly composed of oval or polygonal cells with relatively abundant eosinophilic or clear cytoplasm

(2) spindle cell smooth muscle cells only a minor element in the tumor

(3) may be benign (epithelioid leiomyoma) or malignant (epithelioid leiomyosarcoma)

(4) malignant epithelioid leiomyosarcomas metastasize infrequently

 

where:

• Immunoperoxidase stains will show negative cytokeratin reactivity and be positive for smooth muscle markers.

 

Histologic characteristics:

(1) nuclear grade

(2) necrosis

(3) mitotic activity

 

Nuclear Grade	Features
Grade 1	uniform, bland nuclei with inconspicuous or absent nucleoli and evenly distributed chromatin
Grade 2	intermediate nuclear atypia, often with a small nucleolus
Grade 3	enlarged, hyperchromatic nuclei with prominent macronucleoli and unevenly distributed chromatin

 

Necrosis:

(1) tumor cell necrosis: devoid of intervening zone of reparative connective tissue reaction between necrotic and viable tumor

(2) infarct: central coagulative necrosis with peripheral zone of hyaline fibrosis or granulation tissue interposed between viable and necrotic tumor

 

Mitotic Activity:

(1) area of count: 0.173 mm^2 (diameter 0.47 mm, using 10x ocular and 40x objective lenses)

(2) number of fields counted: 10

(3) five sets of 10 fields counted, and single highest count recorded

 

Features of malignant epithelioid leiomyosarcoma:

(1) significant nuclear atypia (nuclear grade 2 or 3)

(2) mitotic rate at least 3-4 mitoses per 10 high power field

(3) most have tumor cell necrosis