Solitary Keratoacanthoma

Abstract

To discuss the relation between solitary keratoacanthoma (KA) and crateriform squamous cell carcinoma (cSCC), the clinical and histologic features of cutaneous crateriform squamous cell proliferations were studied. Two hundred twenty cases of wholly excised crateriform squamous cell proliferations were studied both clinically (age, sex, location, and duration) and histologically (hematoxylin-eosin-stained sections). For comparison, we studied 100 consecutive cases of wholly excised noncrateriform squamous cell carcinoma (ncSCC). One hundred forty-four of the 220 cases of crateriform squamous cell proliferations were histologically classified as KA. In 47 other cases, a relatively large area of the KA showed frank histologic and cytologic malignant transformation (mKA); this event could happen during every stage of the KA. Twenty-nine lesions were cSCCs without remnants of KA. The patients in the KA group were significantly younger (p = 0.000) than those in the other three groups. The ages of the patients in these three groups were not significantly different (p = 1.0). More KAs (16%) were located in areas that are not usually exposed to the sun than was the case with the other groups of neoplasms considered (2%, 3%, and 3%, respectively), and this difference was statistically significant (p = 0.001). Regarding the duration of the lesion, only the differences between KA and cSCC, KA and ncSCC, and mKA and ncSCC were statistically significant. Not every cutaneous crateriform squamous cell proliferation is a KA; in KA, the crater must be multilocular, the "lips" must be perforated, and the cornified contents do not usually project out of the "mouth." At least a quarter of KAs undergo malignant transformation, which occurs more frequently in older patients and photoexposed areas. This transformation is a focal event and may happen at any stage of KA development. Consequently, a suspected KA must be wholly excised and studied in serial paraffin blocks so as to disclose any focus of malignant transformation.

Keratoacanthoma: a distinct entity?

“…As reported, these metastasizing KA could have been misdiagnosed as KA but are true SCC . In fact 10% as KA diagnosed tumors are malignant and progressing SCC . Hallmarks of malignant tumors such as, prominent mitoses or cytological atypia, are not observed in KA.…”

“…If KA are truly able to form metastasis is still a matter of debate, in contrast with SCC which metastasize in up to 5% . As reported, these metastasizing KA could have been misdiagnosed as KA but are true SCC . In fact 10% as KA diagnosed tumors are malignant and progressing SCC .…”

“…Thereby, both elongated thin tumor lips are covered on the surface and towards the crater by two epidermal sheets which are in parallel with the skin surface. The keratin filled crater plonges into multilocular spaces of epithelial tumor lobules in the periphery in a semi‐star shaped fashion . These are composed of well‐differentiated squamous cells at the dermal interface .…”

Keratoacanthoma: A Clinico-Pathologic Enigma

“…There are a variety of special stains or tests, including expression of lectins, proliferating cell nuclear antigen, vascular cell adhesion molecule (CD‐106) and intercellular adhesion molecule (CD‐54) adhesion molecules, angiotensin type 1 receptor expression, oncostatin M expression, syndecan‐1 expression, MIB‐1 immunohistometry, and stromelysin 3, and ultrastructural features said to be useful in distinguishing the KA from the SCC 48–64 . Sadly, none of the methods, including identification of basal cell carcinomas and KAs by fluorescent lectin staining of a tumor‐specific disaccharide, 49 has proven of practical value.…”

Oral Potentially Malignant Disorders: An Overview of More than 20 Entities

“…According to Sanchez Yus et al 48 at least 24% of KA showed malignant transformation into SCC. KA must be totally excised and studied for any evidence of malignancy.…”