Squamous Cell Carcinoma Arising in Keratoacanthoma: A Neglected Phenomenon in the Elderly

Abstract

Keratoacanthoma is a unique clinicopathologic entity with a behavior and clinical outcome that differs markedly from that of squamous cell carcinoma. The development of squamous cell carcinoma in a keratoacanthoma alluded to by Rook and Whimster in 1979 and by Reed in 1993 was confirmed by Sánchez Yus et al in 2000. We found this phenomenon in 5.7% of keratoacanthomas in a series of 3465 cases. Its incidence in patients older than 90 years was 13.9%. The incidence of perineural invasion in this series of keratoacanthomas was 0.2%.

Different expression of cyclooxygenase-2 (COX-2) in selected nonmelanocytic human cutaneous lesions

“…Epidemiological data indicates a strong relation between the presence of AK and the development of SCC: 82.4% of such skin cancers were found either within (26.7%) or close to (55.7%) actinic keratoses [47]. The estimated ten--year risk of developing SCC against a background of AK is 13-20% [48], while for KA the risk of progression to SCC is 3.6-13.9%, depending on the age group [49]. In our study, the precancerous lesions and SCCs expressed COX-2 at a similar level.…”

The changes in the expression levels of follicular markers in keratoacanthoma depend on the stage: keratoacanthoma is a follicular neoplasm exhibiting infundibular/isthmic differentiation without expression of CK15

“…The histopathological criteria for each stage of KA were based on various textbooks and reviews, as described in detail later in this manuscript. 2 -4,9,12,31 -34 During the process of this careful selection, we eliminated the following cases: (i) 'KA-like SCCs (five lesions)' 35 -37 that histopathologically resembled KA but had an eccentric architecture and prominent atypical cytological features, (ii) 'infundibular and infundibulocystic SCCs (11 lesions)' which have been described elsewhere, 38 and diagnostically challenging cases (six lesions) with regard to whether the lesion was a very early stage of KA or infundibular and infundibulocystic SCC, (iii) 'KA associated with SCC/KA with malignant transformation (four lesions)', 6,7,37 (iv) crateriform SCC arisen from actinic keratosis (four lesions), 6,37 and (v) crateriform Bowen's disease (one lesion). 37 After this careful selection, a total of 67 'pure' KAs, including 16 early or proliferative stage lesions, 43 well-developed stage lesions, five regressing stage lesions and three regressed stage lesions, were chosen from the 98 'KA-like lesions'.…”

Late-Onset Multiple Self-Healing Squamous Epithelioma Ferguson-Smith Recurrence Induced by Radiotherapy

“…The origin and behaviour of KA is controversial: KA is sometimes classified as a variant of SCC, sharing local destructive and metastatic capacity [3]. Others consider KA as a distinct entity due to its particular histology and spontaneous regression [4, 5, 6]. Recent evidence suggests that the gatekeeper mutations underlying the two may be different.…”