Clinical features:
(1) The patient is usually an older adult (>= 60 years of age).
(2) It may affect a patient with xeroderma pigmentosa or with an organ transplantation.
(3) The lesion involves sun-exposed skin (external ear, scalp, etc).
(4) The lesion is firm nodule that may be ulcerated.
(5) The lesion can recur after conservative excision.
Histologic features:
(1) pleomorphic intradermal spindle cell tumor with histiocyte-like cells
(2) population of epithelioid cells with bizarre nuclei, abnormal mitoses and variable multinucleation
(3) a pushing, non-infiltrative advancing margin
Features that suggest another diagnosis:
(1) absence of actinic damage
(2) tumor necrosis
(3) vascular or perineural invasion
The diagnosis requires exclusion of other diagnoses including:
(1) Merkel cell carcinoma
(2) atypical fibrous histiocytoma
(3) spindle cell squamous cell carcinoma
(4) malignant melanoma
(5) metastatic carcinoma
