SLAM Differential for Dermal Spindle Cell Tumors

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SLAM DDx

This sketch covers malignant dermal spindle cell proliferations abutting the epidermis, or “slammed” up against the dermis. This category includes spindle cell squamous cell carcinoma, leiomyosarcoma, atypical fibroxanthoma, and desmoplastic or spindle cell melanoma. These tumors share overlapping spindle cell morphology but differ in epidermal involvement, cytologic features, stromal characteristics, immunohistochemical staining profiles, and associated inflammatory or degenerative changes. Spindle cell squamous cell carcinoma shows malignant spindle cells with overlying epidermal keratinocytic atypia and variable epidermal connection and is positive for cytokeratins, p63, and p40 with CK5, CK6, CK903, and MNF116 expression. Leiomyosarcoma demonstrates hyperchromatic spindle cells arranged in fascicles with cigar shaped nuclei, perinuclear vacuoles from glycogen, and smooth muscle differentiation marked by SMA and desmin positivity. Atypical fibroxanthoma presents with pleomorphic spindle cells, bizarre mitotic figures, multinucleated giant cells, histiocyte like and foam cells, and typically expresses CD10 and CD68 with possible SMA positivity in a tram track pattern. Desmoplastic or spindle cell melanoma is characterized by spindle cells in a fibrotic or myxoid stroma with solar elastosis, lymphocytic aggregates, frequent perineural invasion, and immunoreactivity for S100, SOX10, and p75 with S100 being variably sensitive.

S = Spindle cell squamous cell carcinoma
L = Leiomyosarcoma
A = Atypical fibroxanthoma
M = Melanoma, specifically desmoplastic or spindle cell type

Spindle Cell Squamous Cell Carcinoma

  • Angry red scaly crab with spool = Spindle cell SCC
  • Abnormal carrots = Overlying epidermal keratinocytic atypia
  • Digging up above ground = May have epidermal connection
  • Carrots = Cytokeratins
    • Hive = CK5 positive
    • Sticks = CK6 positive
    • Vines on a tree = CK903
    • Monday Night Football = MNF116
  • Parking gate stick = p63 positive
  • Fort = p40 positive
  • Magnifying glass = Most specific for SCC especially compared to AFX

Leiomyosarcoma

  • Angry lion = Leiomyosarcoma
  • Fascicle ropes = Hyperchromatic spindle cells with fascicular architecture
  • Cigars = Cigar shaped nuclei
  • White glycogen cookie jar = Perinuclear vacuoles from glycogen
  • Smash = SMA positive
  • MITT = Desmin positive

Atypical Fibroxanthoma

  • Carwash = AFX
  • Bizarre purple headlights = Bizarre atypical mitotic figures
  • Pink car with purple dots = Multinucleated giant cells
  • History textbook = Histiocyte like cells
  • Foamy soap = Foam cells
  • Spool = Spindle cells
  • SMAshed train track = May have SMA positive tram track pattern
  • 10 out of 10 service = CD10 positive
  • 68 plate = CD68 positive

Desmoplastic or Spindle Cell Melanoma

  • Angry black disco crab with a spool = Desmoplastic or spindle cell melanoma
  • Blue gray wavy goo with purple dots = Solar elastosis and blue gray myxoid stroma
  • Clusters of purple limes = Lymphocyte aggregates
  • Noodles = Perineural invasion
  • 100 dollar bill = S100 positive
  • Funky socks = SOX10 positive
  • Heavenly hive = p75 (NGFR) positive