Superficial Soft Tissue Tumors of the Skin

Victor G. Prieto, MD, PhD Professor of Pathology and Dermatology

Head of Dermatopathology

UT-MD Anderson Cancer Center Houston, Texas

Summary • Introduction • Selected entities (update, clinical relevance, differential diagnosis) • Main Features: – Clinical – Histological – Immunohistochemical

Introduction • Spectrum: reactive to malignant (clinical relevance) • Objection of some purists • Almost any soft tissue tumor can occur in the skin (subcutaneous o subfascial) �Skin biopsy�

Atypical Fibrohistocytic Lesions

• Classic concept: DF is a benign lesion completely different from DFSP, based on histologic and clinical features • Use of immunohistochemistry • But some times the differences are not so clear…

• Intermediate between DF y DFSP • Trunk, 0.6-2 cm, recurrence • Acanthosis and hyperpigmentation • Storiform pattern Horenstein et al. Am J Surg Pathol 2000; 24: 996-1003

Atypical Fibrohistiocytic

Lesions

• Keloidal collagen • Storiform pattern

• Keloidal collagen

• Infiltration of subcutaneous tissue

• Cellular atypia • Mitotic figures

FXIIIa CD34

Key Points • The immunophenotype of these lesions suggests a differentiation between DF and DFSP • Possibility of local recurrence • Achieve complete excision

Epithelioid Fibrous Histiocytoma

• Papule / nodule of 0.5 - 2 cm • Non pigmented or tan colored, elevated • Extremities in adults

• Dermal lesion, circumscribed • Collarette • No epidermal involvement

• Epithelioid cells, eosinophilic-clear • Regular nuclei with small nucleoli

• Focal keloidal collagen

S100 Protein

CD68

Factor XIIIa

Differential Diagnosis • Melanocytic lesions: – No pigment, no intraepidermal

component – S100 protein- (dendritic cells!) – HMB45, MART1 – HAM56, (CD68)

Key Points • Include this entity among the differential diagnosis of unusual melanocytic lesions • Immunohistochemistry in case of doubt

Superficial Acral Fibromyxoma

• Solitary mass on hands and feet • Asymptomatic

• 75-year-old white woman • Left palm lesion for 3 - 4 months • 1.7 x 1.5 cm • Asymptomatic, flesh-colored nodule

• Poorly circumscribed • Dermis • Spindle cells

• Close to epidermis • (No intraepidermal component

• Loose storiform pattern • Vascular

SMA

FXIIIa

CD34

Key Points • Adults • Same as cellular fibroma • Recurrence • DDx DFSP, DF

Epithelioid Sarcoma

• Papule / nodule of 0.5 - 2 cm • Non pigmented or tan colored, elevated • Extremities in young adults

• 25 yo man • Soccer player (goalie) • Lesion started �after� trauma to

the finger

• Ulcer • Acanthosis (~prurigo nodularis

• Central necrosis

Epithelioid cells Central necrosis

Distant metastasis (elbow)

Keratin

Differential Diagnosis • Granulomatous dermatitis: – Mucin (granuloma annulare) – Fibrin (rheumatoid nodule) – Multinucleated giant cells (necrobiosis

lipoidica) – Keratin! – Loss of INI NI1 (SWI/SNF chromatin

remodeling complex) Chr 22q11.2

Key Points • Include this entity among the differential diagnosis of unusual �granulomatous� dermatitides (young, fingers) • Immunohistochemistry in case of doubt

Plexiform Fibrohistiocytic Tumor • Uncommon neoplasm of intermediate malignancy • Dermis or subcutaneous tissue, on trunk and extremities in children and young adults Enzinger/ Zhang, Am J Surg Pathol 1988;12:818

• Infiltrative tumor, plexiform, small nodules • Short fascicules

• Infiltrative, plexiform, small nodules

Short fascicules with fusiform cells (fibroblasts y myofibroblasts) (sometimes the only component)

Macrophages and multinucleated giant cells (osteoclastic type)

Differential Diagnosis • Cellular DF / atypical fibrohistiocytic lesion • DFSP Both lack plexiform pattern or osteoclastic cells • Giant cell tumor of tendon sheath

Key Points • Children and young adults • Short fascicles of spindle cells • Macrophagic giant cells • Recurrent

Fibrous Hamartoma (of Infancy)

• First year of life (23% congenital) • Axilla, arm, trunk, groin, and genital area • Solitary, asymptomatic, sometimes quick growth • t(6;12;8)(q25;q24.3;q13); t(2;3)(q31;q21) • Recurrence

Triphasic pattern: • Fascicles of fibroblasts • Adipocytes • Fusiform cells (�primitive� mesenchyma)

Three components

Fusiform cells

Fascicles Mesenchyma/nerves

Differential Diagnosis

• Neurofibroma • Giant cell tumor of tendon sheath

Key Points • Triphasic pattern • Similarities with neural lesions (neurofibroma, neurofibrosarcoma, schwannoma) • Negative for S100 protein

Neurothekeomas • Harkin and Reed (1969), Gallager (1980) • Superficial tumor of purported nerve sheath origin • Head and neck, extremities • Cellular and myxoid • Myxoid variant of the cellular type

• Dermal nodule • Fascicles

Myxoid background

Small cells, myxoid stroma S100

Dermal nodule

Fascicles

Epidermis is spared

Uniform cells, fibromyxoid stroma

• Spindle, fusiform cells • Fibrous stroma

Ki67

S100 A6

Histologic Features • 25% moderate cytologic atypia (very rarely marked) • Mitotic figures 0 - > 10/mm2 • Pattern whorled or fascicular • Different amounts of myxoid background

IPOX Features • S100 in myxoid lesions (nerve sheath myxoma) • S100A6 in neurothekeoma • NKI/C3, CD10, microphthalmia transcription factor, and PGP9.5 • Focal expression of SMA and CD68

Key Points • Possibly two types (cellular/myxoid) • Myxoid variant of cellular NTK • S100 in the myxoid • S100 A6 in the cellular • Mostly non-aggresive • Careful with melanoma (S100)

Ossifying Fibromyxoid Tumor of Soft Tissue

• Very rare, circumscribed • Deep nodules, slow growth • Trunk and extremities, 1 to 14 cm

• Fibrous capsule, ring of mature bone

• Fusiform or epithelioid cells • Irregular fascicles

• Myxoid areas

OFMST: Atypical Variant

• 20% of cases show local recurrence !!!!!!!! • 10% distant metastases • Infiltrative border

• Infiltrating border, hypercellularity, high nuclear grade, more than 2 mit/50 HPF

Atypical variant

Key Points • Gross the hard areas at the periphery of the lesion • Mixture of fibrous and myxoid areas • Atypical variant

Pleomorphic Hyalinizing Angioectoid Tumor of Soft Parts • Firm, lobulated, tan, with focal hemorrhage, several cm in size • Lower extremity, middle age • Infiltrative, deep dermis and subcutaneous tissue • Local recurrence (50%)

• Loose connective stroma • Dilated vessels, hyaline ring

• Dilated vessels, fibrin

• Fusiform and epithelioid cells with pseudoinclusions • Pleomorphic cells (~ MFH) • Rare mitotic figures • Negative anti-S100

PHAT: DDx • �Ancient� schwannomas (dilated vessels with hyaline and nuclear pseudoinclusions) circumscribed, S100+ • MFH lacks hyalinized vessels, nuclear pseudoinclusions o CD34 expression. Numerous mitotic figures • Vascular tumors (hemangioma, hemangioendothelioma). CD31 and FVIIIra

S100 Protein

Key Points • Hyaline vessels • Nuclear atypia • Rare mitotic figures • Negative S100 protein

Acral Myxoinflammatory Tumor with Atypical Giant

Cells • Inflammatory myxohyaline tumor of the extremities with virocytes or Reed-Sternberg cells • Inflammatory myxoid tumor of soft parts with atypical giant cells

AMTAGC • Rare, adults and older individuals • Distal extremities (hands and feet) • Frequent local recurrence (metastasis) • 1 - 6 cm • Clinical Dx: ganglion, tenosynovitis, giant cell tumor of tendon sheath

• Multinodular, infiltrative, ~hamartoma

• Fibrous stroma, pleomorphism

Key Points

• Infiltrative • Mixed with adipose tissue • Large, �virocytes� • (Metastasis)

Soft Tissue Lesions in the Skin: Summary

• At least five �new� lesions recently described • Possibility of local recurrence (even metastasis) • In case of doubt, complete excision

Pigmented Melanotic Schwannoma

• Paraspinal

• 20-50% recurrence or metastasis

• Unclear histogenesis

C5, 36 yo man

• Infiltrating border, hypercellularity, high nuclear grade, more than 2 mit/50 HPF

• Psammoma bodies • Cytologic atypia

• S100

• MART1

• HMB45

Key Points • �Melanoma� in the wrong place • Rule out metastasis • Schwannian features (EM) • Recurrence and metastasis