Selected Pseudomalignant Soft Tissue Tumors of the Skin and Subcutis

Selected Pseudomalignant Soft Tissue Tumors of the Skin and Subcutis Andrew L. Folpe, M.D. Professor of Laboratory Medicine and Pathology Mayo Clinic, Rochester, MN folpe.andrew@mayo.edu 2016 MFMER slide-1

Overview Fibrous histiocytoma variants Pediatric proliferative fasciitis Cellular neurothekeoma 2016 MFMER slide-2

Cellular Fibrous Histiocytoma Proximal extremities, head and neck Lightly eosinophilic spindled cells, fascicular to storiform pattern Lacks siderophages, giant cells and foam cells Necrosis in 10%; mitotic figures frequent Limited involvement of subcutaneous fat Key is recognition of ordinary BFH 20-30% local recurrence rate Complete excision recommended 2016 MFMER slide-3

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Factor XIIIa CD34 2016 MFMER slide-8

Factor XIIIA CD34 CD68 S100 2016 MFMER slide-9

CD34 2016 MFMER slide-10

DFSP 2016 MFMER slide-11

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CD34 2016 MFMER slide-13

Aneurysmal Fibrous Histiocytoma Darkly pigmented, often thought to be vascular or melanocytic tumor May be large at time of diagnosis Plump spindled cells in a fascicular to tight storiform pattern Hemorrhage with siderophages Key is identifying features of ordinary BFH Behavior similar to C-BFH 2016 MFMER slide-14

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Angiomatoid (malignant) fibrous histiocytoma Children and young adults Subcutis and deep dermis of extremities, trunk, head and neck Systemic symptoms Fibrous pseudocapsule with pericapsular lymphocytic infiltrate Pseudovascular spaces in 50% Traumatized cases may show extensive hemorrhage and fibrosis Generally bland histiocytoid cells, sometimes with hemosiderin pigment in fascicular and whorling patterns Degenerative nuclear atypia Positive for CD68, desmin (50%), EMA (50%) EWSR1-CREB1, EWSR1- ATF1, FUS-CREB1, FUS-ATF1 Local recurrences common; LN and distant metastases rare (2-5%) 2016 MFMER slide-17

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EMA Desmin CD68 2016 MFMER slide-21

Atypical Fibrous Histiocytoma Clinically similar to conventional BFH/ dermatofibroma Low power resemblance to ordinary BFH High power examination shows foci of markedly atypical, sometimes multinucleated cells, with mitotic figures (including atypical forms) Behavior similar to cellular BFH 2016 MFMER slide-22

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AFX and Undifferentiated Dermal Sarcoma Usually much older patients Sun damaged skin Absence of areas of BFH 2016 MFMER slide-26

Metastasizing BFH Approximately 20 reported cases Most often associated with cellular FH, but reported with all subtypes May be related to repeated local recurrences No histologic features of primary tumors predictive of metastasis Cases reported as cystic fibrohistiocytic tumor of the lung represent metastatic BFH Prognosis generally favorable if metastases can be completely resected; rare deaths from disease 2016 MFMER slide-27

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Pediatric Proliferative Fasciitis 2016 MFMER slide-30

Proliferative fascitis 2016 MFMER slide-31

Proliferative myositis 2016 MFMER slide-32

Usually small and superficial Highly cellular with sheets of ganglion-like myofibroblasts Mitotically active Necrosis Prominent neutrophilic inflammatory infiltrate Easily confused with proximal type epithelioid sarcoma/ extrarenal rhabdoid tumor 2016 MFMER slide-33

Pediatric proliferative fascitis 2016 MFMER slide-34

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Pediatric PF Epithelioid sarcoma 2016 MFMER slide-39

Keratin SMARCB1 2016 MFMER slide-40

Cellular Neurothekeoma 2016 MFMER slide-41

Cellular Neurothekeoma Unrelated to nerve sheath myxoma (myxoid neurothekeoma) Head/ neck and proximal upper extremity of young adults Present as painless flesh colored papules or nodules Distinctly nested to fascicular growth pattern Subtle whorling arrangement of tumor cells within nests Abundant eosinophilic cytoplasm and round to oval nuclei Nuclear atypia and mitoses may be present Myxoid change may mimic nerve sheath myxoma Express some combination of SMA, CD10, MiTF and NKI/C3 Limited potential for local recurrence 2016 MFMER slide-42

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Plexiform fibrohistiocytic tumor 2016 MFMER slide-50

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