Common Soft Tissue Tumors/Proliferations

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 1) (see Ch. 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 1, 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.

Pathogenesis involves clonal integration of Merkel cell polyoma virus DNA into the host genome in ∼80%; UVR-signature mutations in the remainder.

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: consider baseline Merkel cell polyomavirus serology for prognostic significance and to track disease; 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). For metastatic disease, consider a checkpoint inhibitor (e.g. pembrolizumab) or chemotherapy (e.g. etoposide and carboplatin).

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

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

Can become irritated or infarcted.