• Skin-colored to pink, soft papulonodule, often on the trunk (see Fig. 50.2).

• Compressible (the tumor often herniates inward upon palpation – this is referred to as the ‘button-hole’ sign); it is sometimes pedunculated.

• Usually solitary in most individuals.

• When multiple, need to distinguish linear form (segmental; mosaic) from a generalized distribution pattern (neurofibromatosis type I) (see Chapter 50).

• Histopathology: wavy, delicate spindle cells with tapered nuclei in a pink stroma.

• Plexiform type has been likened to a ‘bag of worms’ (Fig. 95.1); it is generally on the trunk and proximal extremities, highly associated with neurofibromatosis type I, and prone to malignant degeneration (2–13%).

• Solitary, pink-yellow, soft, smooth papulonodule; generally seen in adults.

• Often on the extremities or head (Fig. 95.2).

• Asymptomatic (rarely painful).

• Histopathology: encapsulated tumor with foci of wavy, spindled nuclei in palisades and foci of myxoid change.

• Often in adults; skin-colored to brown-red, firm papulonodule; sometimes ulcerated or verrucous.

• 30% on the tongue.

• Multiple tumors in 10% of patients.

• Histopathology: polygonal cells with oval nuclei and characteristic granular cytoplasm.

• Skin-colored papulonodule(s) at a site of prior trauma.

• Often painful or ‘sensitive’ (Fig. 95.3).

• Histopathology: haphazardly distributed fascicles of spindle cells with tapered nuclei.

• In older adults; solitary, rapidly growing, pink to red to violaceous nodule (Fig. 95.4).

• Commonly on the head and neck.

• Aggressive behavior: distant metastases in 40%; 70% survival at 5 years if primary lesion is <2 cm in diameter; 18% survival at 5 years if distant metastatic disease.

• Histopathology: islands or trabeculae of blue cells that on high-power magnification have chromatin that appears speckled like ‘salt and pepper’; characteristically cytokeratin 20 (CK20)-positive and thyroid transcription factor-1 (TTF1)-negative.

• Rx: optimally includes wide excision, accompanied by sentinel lymph node biopsy (SLNB); adjuvant radiation treatment recommended for most patients (exceptions: primary ≤1 cm, SLNB negative, no immunosuppression).

• Common; skin-colored to pink or occasionally hyperpigmented, pedunculated papule.

• Sites of predilection: neck, axilla, groin (Fig. 95.5).

• Can become irritated or infarcted.

• Solitary, skin-colored to pink, shiny papule; commonly on the nose (Fig. 95.6).

• When multiple, need to consider genodermatoses (e.g. tuberous sclerosis, multiple endocrine neoplasia type I).

• Histopathology: stellate spindle cells in a hyalinized stroma with dilated vessels.

• DDx: basal cell carcinoma, intradermal melanocytic nevus, adnexal tumors.