Sclerosing Epithelioid Fibrosarcoma.--Sclerosing epithelioid fibrosarcoma (SEF) is a distinctive fibroblastic neoplasm characterized by epithelioid tumor cells arranged in nests, cords, or sheets embedded within a sclerotic collagenized matrix.
Sclerosing epithelioid fibrosarcoma. In: Fletcher CD, Bridge JA, Hogendoorn PCW, Mertens F, eds.
Amplification and overexpression of MDM2, CDK4, GL1 and SAS genes of the 12q13-15 region has been associated with other sarcomas such as well-differentiated and dedifferentiated liposarcoma, leiomyosarcoma, and a significant subset of alveolar and embryonal rhabdomyosarcomas  and even sclerosing epithelioid fibrosarcoma .
Mandahl, "Amplification of 12q13 and 12q15 sequences in a sclerosing epithelioid fibrosarcoma," Cancer Genetics and Cytogenetics, vol.
Histopathologically, the differential diagnoses include sclerosing epithelioid fibrosarcoma
, calcifying fibrous pseudotumor of digits, malignant peripheral nerve sheath tumor, synovial sarcoma, ossifying hematoma, and an ossifying epithelioid hemangioendothelioma.
Other more-rare entities that differ in treatment but morphologically resemble ILC and may involve the breast include metastases of signet ring carcinomas from other primary sites, sclerosing epithelioid fibrosarcoma, myeloid sarcoma, mucosa-associated lymphoid tissue lymphoma, and plasma cell dyscrasias.
Sclerosing epithelioid fibrosarcoma also resembles, and should be included in the differential diagnosis of, ILC, especially when cytokeratin and ER IHC stain results are negative.
Differential diagnostic entities to consider include IDC-L, metastatic signet ring cell carcinomas, sclerosing epithelioid fibrosarcoma, and primary or secondary leukemic or lymphomatous involvement of the breast.
MUC4 is a useful marker for low-grade fibromyxoid sarcoma (LGFMS) and sclerosing epithelioid fibrosarcoma (SEF; Figure 5).
Sclerosing epithelioid fibrosarcoma, another fibroblastic neoplasm, shows morphologic and molecular overlap with LGFMS, and hybrid tumors showing features of both exist.
Sclerosing epithelioid fibrosarcoma
primary of the bone.
Many recently reported diagnostic markers are described in this article, such as (1) signal transducer and activator of transcription 6 (STAT6) as the most sensitive and specific IHC marker for solitary fibrous tumor; (2) loss of antihistone H3 acetyl K27 trimethylation (H3K27) nuclear expression in 50% of malignant peripheral nerve sheath tumors, particularly in high-grade malignant peripheral nerve sheath tumors; (3) mucin 4 (MUC4) expression in low-grade fibromyxoid sarcomas and sclerosing epithelioid fibrosarcomas
; and (4) nuclear expression of calmodulin binding transcription activator 1 (CAMTA1) in epithelioid hemangioendotheliomas.