Keratoacanthoma (KA)

• Typically considered to be variant of SCC; may spontaneously regress or occur as multiple lesions
• Presents as rapidly enlarging papule or nodule often appearing crateriform with keratotic center, typically in sun-exposed areas
• Different presentations: solitary, multiple, giant, keratoacanthoma centrifugum marginatum, KA associated with Muir–Torre syndrome (GI cancer and sebaceous neoplasms), generalized eruptive KAs (Grzybowski or Ferguson-Smith type)
  • KA centrifugum marginatum: may reach several centimeters in diameter, concomitant expansion of border and central healing
  • Giant KA: rapid enlargement of nodule to several centimeters
  • Ferguson-Smith type: sudden-onset of multiple KAs in childhood, which will slowly resolve on their own
  • Grzybowski type: sudden-onset of multiple KAs in adulthood (eruptive pattern)
• Histology: symmetric tumor with acanthotic epidermis consisting of well-differentiated squamous cells with glassy cytoplasm, central invagination of neoplasm filled with keratin and epithelial lips extending around both sides of crater, prominent inflammatory infiltrate around lesion
• Treatment: complete excision typically performed, observation alone (if lesion following an involutional pattern)

Figure 5.8 A: Keratoacanthoma (Courtesy of Dr. Paul Getz) B: Keratoacanthoma C: Keratoacanthoma

Figure 5.9 A: Morpheaform BCC B: Nodular BCC C: Ulcerated BCC