Table 2 Morphophenotypic features of the most common mesenchymal spindle cell neoplasms in the differential diagnosis of EESS

Cellular leiomyoma/low-grade leiomyosarcoma

characteristic intersecting fascicles of smooth muscle cigarshaped spindle cells with eosinophilic cytoplasm and perinuclear vacuolation, showing a smooth, pushing margin and large, irregular, thick-walled blood vessels

muscle-specific actin +, smooth muscle actin +, desmin +, ER +, PgR+, CD10 −/+, H-caldesmon +

Gastrointestinal stromal tumor

spindle cells with long tapering nuclei and abundant clear or eosinophilic cytoplasm arranged in fascicles or sheets; characteristically well circumscribed with pushing borders

CD34 +, DOG-1 +, CD117 +, CD10 -, ER -, PgR-; muscle-specific actin −/+, smooth muscle actin −/+, desmin −/+,

Solitary fibrous tumor

bland spindle cells haphazardly arranged in a dense collagenous matrix but lacks the peculiar characteristic vasculature of the ESS

CD34 +, CD10 -, ER -, PgR-

Monophasic synovial sarcoma

most commonly involves the soft tissues of the extremities;

CD99 +, EMA +, CD10 -, ER -, PgR-

ESS

monomorphous plump spindle cells forming short regular fascicles, evenly distributed arterioles and infiltrative border

muscle-specific actin −/+, smooth muscle actin −/+, desmin −/+, ER +, PgR+, CD10 +, H-caldesmon -