MELANOCYTIC COLLISION TUMORS

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MELANOCYTIC COLLISION TUMORS

• Christopher R. Shea, MDProfessor and
  ChiefSection of DermatologyUniversity of Chicago

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Case 1 Clinical

• 32-year-old white man
• 8 mm pigmented lesion
• 7 mm underlying nodule of back
• Excisional specimen interpreted at outside
  hospital as desmoplastic melanoma
• Clark level IV
• Breslow thickness 5.5 mm
• Wide excision no residual tumor
• Bilateral axillary SLN biopsies no metastatic
  disease (0/2)

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Case 1 Pathologic

• Proliferation of melanocytes in nests and as
  single cells at DEJ and in papillary dermis
• No suprabasal melanocytosis
• Moderate to severe cytologic atypia
• Dermal fibrous lesion composed of spindle cells
  with focal storiform pattern

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S-100
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S-100
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HMB-45
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CD34
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fXIIIa
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Case 1 Diagnosis

• Collision of
• Atypical junctional melanocytic nevus
• Dermatofibroma

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Case 2 Clinical

• 35-year-old white man in good health
• One-year history of hard, subcutaneous right
  abdominal wall mass
• Case referred in consultation to rule out
  desmoplastic melanoma

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Case 2 Pathologic

• Proliferation of melanocytes with mild atypia in
  nests
• Junctional comonent extends peripherally beyond a
  central, intradermal component
• Bridging of rete ridge architecture
• Dermal fibrosis, perivascular infiltrate of
  lymphocytes and macrophages
• Deeper in dermis, spindle cells in fibrous stroma

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S-100
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CD34
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Case 2 Diagnosis

• Collision of
• Compound melanocytic atypical nevus
• Dermatofibroma

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Case 3 Clinical

• 67-year-old white woman
• Lesion of left cheek of unknown duration
• Clinical diagnosis rule out superficial
  spreading malignant melanoma

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Case 3 Pathologic

• Atypical melanocytes in confluent, single-cell
  and nested patterns at basal layer
• Dermal lobular proliferation of spindled cells
  with delicate nuclei and elongated, eosinophilic
  cytoplasmic processes
• IHC not performed

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Case 3 Diagnosis

• Collision of
• Melanoma in situ (lentigo maligna type) vs.
  atypical nevus
• Neurofibroma

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Case 4 Clinical

• 68-year-old white woman
• Lesion of right upper lip
• Excisional specimen interpreted at outside
  hospital as desmoplastic melanoma
• Clark level IV
• Breslow thickness 4.3 mm

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Case 4 Pathologic

• Epidermal atrophy
• Single-cell proliferation of hyperchromatic,
  large melanocytes at basal layer
• Dermis elastotic
• Large dermal nodule composed of delicate spindle
  cells in myxoid-fibrillary stroma containing
  mast cells
• No significant atypia of dermal component

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S-100
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GFAP
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Case 4 IHC

• S-100 protein, gp100 (HMB-45) positive on
  epidermal lesion only
• Dermal spindle cells negative for S-100, gp100,
  GFAP, NKI-C3
• IHC findings do not support dermal component of
  desmoplastic melanoma, neurothekeoma, myxoid
  neurofibroma

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Case 4 Diagnosis

• Collision of
• Melanoma in situ (lentigo maligna type)
• Cutaneous myxoma
• Differential diagnosis
• Mucocele of lip

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Case 5 Clinical

• 63-year-old white man
• Lesion of left hand
• Shave biopsy specimen interpreted at outside
  hospital as likely melanoma
• Referred for pathologic consultation

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Case 5 Pathologic

• Epidermis hyperpigmented, with increased numbers
  of enlarged melanocytes
• Single cells at basal layer
• Suprabasal spread focally
• Dermal elastosis
• Diffuse interstitial and palisaded population of
  epithelioid and spindled cells
• Basophilia and degeneration of dermis

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S-100
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S-100
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HMB-45
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CD68
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Case 5 Diagnosis

• Collision of
• Atypical melanocytic proliferation (secondary to
  chronic actinic damage versus evolving MMIS)
• Granuloma annulare

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Case 6 Clinical

• 61-year-old man
• Lesion of back
• Clinical diagnosis atypical dermatofibroma

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A wide resection was performed
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Case 6 Pathologic

• Shave biopsy
• Epidermal hyperpigmentation with junctional
  hyperchromatic melanocytes singly and in nests
• Dermal spindled-cell tumor in fascicles, having
  high-grade nuclear atypia and mitotic figures
• Excision
• Epidermal proliferation of confluent single
  melanocytes with atypia and focal suprabasal
  spread
• Dermal spindled-cell lesion with perineural spread

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S-100
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S-100
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HMB-45
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HMB-45
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HMB-45
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CD34
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fXIIIa
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SMA
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HMF-35
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Case 6 IHC

• S-100 positive in junctional melanocytes
• Dermal lesion positive for smooth-muscle actin,
  negative for S-100, gp100 (HMB-45), Mel-5, CK22,
  desmin

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Case 6 Diagnosis

• Controversial
• ? Collision of
• Melanoma in situ
• Leiomyosarcoma or AFX
• ? Unusual spindle-cell melanoma with divergent
  phenotype
• Lacking S-100 expression but having strong actin
  expression

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Discussion Collision Tumors

• Coexistence of two or more neoplasms
• May be pathogenetically related or unrelated
• Melanocytic lesions adjacent to dermal spindle
  cell lesions may be misinterpreted as evidence of
  desmoplastic melanoma
• Desmoplastic melanoma often underdiagnosed
• Index of suspicion may be high
• Immunohistochemical study may be helpful in
  clarifying the divergent histogenesis
• Avoid the erroneous diagnosis of deeply invasive
  spindle-cell melanoma, which may trigger
  excessively aggressive management

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Occams Razor

• Principle of parsimony
• Entia non sunt multiplicanda praeter necessitatem
  (Entities should not be multiplied beyond
  necessity)
• William of Occam c. 1285 -1347)

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• Everything should be made as simple as possible,
  but not simpler.
• - Albert Einstein