In a general surgical pathology practice, many different types of lesions are removed over concern that they might be this malignant skin tumor...concern for basal cell carcinoma (BCC) or squamous cell carcinoma (SCC). The mimics include:

• benign lesions:
  1. "fibrous papule of nose" mimics BCC [S-01-8120]; and, a "fibrous papule" can have some bizarre fibroblasts and increased vascularity [S-02-5498].
  2. enlarged sebaceous gland (or seb. gland nevus [S-04-13542]) mimics BCC[S-01-6494c].
  3. melanocytic nevi may mimic BCC.
  4. soft tissue skin nodules:
     • muscle:
       1. solitary & multiple piloleiomyomata (arrector pili muscle hamartoma): tender intradermal nodule [S-04-2917].
       2. genital leiomyoma: located scrotum, labia, and areola & usually not tender.
     • vascular:
       1. angioleiomyoma: well-circumscribed, painful dermal & sub-Q nodule from vascular wall.
     • neural:
  5. "actinic papule": is usually a not-very-keratotic actinic keratosis presenting a "fibrous papule"-like (composed mostly of actinic dermal elastotic deposits) bump which mimics BCC [S-01-6454; S-05-1866; S-05-1867] and can sometimes have LSC-like superimposed change due to "picking" [S07-12702].
  6. "actinic granuloma" (GA in actinic skin?; granuloma containing actinic elastotic material) mimics BCC [S-01-4041].
  7. "actinic keratoses" (AK) mimic SCC:
     • acantholytic hyperkeratotic AK [S-02-11712].
     • warty dyskeratoma mimics AK/BCC/PMK/SCC [S-02-11439; S-04-10438], Grover-like/Darier's-like acantholytic dyskeratosis.
     • PMKs (AK with squamous dysplasia) mimic SCC.
     • "actinic keratoses" (AK) w/ lichenoid component mimic BCC [S-04-13588].
  8. rosacea-like granulomatous ruptured follicle mimics BCC [S-01-6494a].
  9. isolated subepidermal pustule mimics BCC [S-01-3570].
  10. focal chronic stasis dermatitis on legs mimics SCC [S-01-6491].
  11. chronically inflamed actinic keratosis mimics SCC [S-01-8124].
  12. benign "fibroepithelial nevus" mimics BCC [S-01-10765].
  13. dermatofibroma mimics BCC [S-02-6393].
  14. Grover like actinic keratosis mimics BCC [S-07-6904].
  15. nonspecific "chronic inflammatory papules" mimic cutaneous lymphoma [S-02-5576].
  16. sessile hyperkeratotic papilloma secondarily involved by MC (molluscum contagiosum) or HPV 60 or HPV 65 (all 3 have large intracytoplasmic eosinophilic inclusions) mimics SCC[S-01-11698]. 
  17. lichenoid or lichen planus-like keratosis [S-01-10339; S-03-5885].
  18. hypertrophic lichen planus.
  19. hypertrophic discoid lupus lesion.
  20. eruptive keratoacantomas [S08-562].
  21. seborrheic keratosis: ordinary pigmented, irritated lesions may pose concern for melanoma; but pigmented intraepidermal epithelioma variants especially so [S-05-9543].
  22. dermatosis papulosa nigra: pigmented papules on the face of blacks...could be a worry for melanoma or BCC [S-05-7624].
  23. plantar keratoma: [LMC-02-4917] a very hyperkeratotic clavus (clavus synonyms include the following: callosity, a hyperkeratotic response to trauma; corn, heloma or a circumscribed hyperkeratotic lesion that may be hard [i.e., heloma durum] or soft [i.e., heloma molle]; and callous or callus or a diffusely hyperkeratotic lesion. Localized callosities of the soles, which do not resolve, are termed plantar callus, heloma, tyloma, keratoma, or plantar corn. When callosities occur over one or more lateral metatarsals, they are termed intractable plantar keratoses)...mimics SCC.
  24. angiokeratoma: combination of dilated superficial vessels and epidermal hyperplasia & hyperkeratosis...there are sporadic, isolated lesions and then various named entities...dark & mimics melanoma.
  25. dilated pore of Winer and/or the more elaborate (proliferating pore) "pilar sheath acanthoma¹" [S-04-13368] (may harbor a cancer of follicular duct epithelium)...dark and like a blackhead, darkness mimics melanoma or BCC.
  26. various skin epithelial cysts are smooth and could mimic a nodular BCC or dermal tumor:
      • epidermal inclusion cyst (EIC...follicular infundibular cyst).
      • granulomatous milium cyst [S-05-924].
      • pilar sheath acanthoma¹: see above; squamous microsinuses lateral in dermis from a pore and may even involve subdermal tissue.
      • dilated pore of Winer, see above.
      • trichilemmal cyst: no granular layer in lining cells; contents of cheesy, rancid homogeneous eosinophilic matter.
      • steatocystoma: thin epithelial lining with sebaceous cell clusters & corrugated keratin & oil contents.
      • hair matrix cyst: lots of basaloid cell component in wall (fore-runner of pilomatricoma).
      • apocrine cystadenoma: contains homogeneous eosinophilic fluid & lining cells with decapitation secretion.
      • eccrine hydrocystoma: cuboidal to flattened eccrine-like lining cells and dark fluid contents; may lose roof and become papillated ("benign eccrine papilloma of skin surface" [S07-12701]).
      • syringocystadenoma papilliferum: two-cell-layered lining papillations and stroma filled with plasma cells.
      • hidradenoma papilliferum: two-cell lining & stroma not filled with plasma cells & papillary stalks which can extend through a surface pore "like a hermit crab".
  27. other
• borderline lesions:
  1. premalignant keratosis (PMK) mimics BCC [S-01-8239].
• other malignant lesions:
  1. malignant fibrous histiocytoma (MFH) mimics SCC; MFH must be K903 negative (spindled SCC positive).
  2. hypertrophic PMK in center of multifocal superficial BCC mimics SCC [S-01-11950].

References:

1. Murphy GF, Dermatopathology..., 1995. (EBS office)

(posted June 2001; latest addition/update 15 September 2008)