CPC13: Comparative study of p16, p53 and Ki67 immunostaining indicates that keratoacanthoma and cutaneous squamous cell carcinoma are clinicopathologically distinct entities

Keratoacanthoma (KA) is widely considered a benign, usually self‐resolving entity distinct from cutaneous squamous cell carcinoma (cSCC), while some consider KA to be indistinguishable histologically from cSCC. Published studies have indicated a use for p16, p53 and Ki67 immunohistochemistry in the assessment of KA and cSCC. We carried out an audit of comparative clinical features and staining patterns for p16, p53 and Ki67 used in the routine reporting of fully excised KA (excluding late regressing lesions), cSCC with KA‐like features (cSCC‐KAL) and other cSCC (cSCC‐OTHER). Cases were classified according to the Royal College of Pathologists Dataset for reporting cSCC. To ensure diagnostic concordance, all cases were reviewed by three dermatopathologists. There were 25 cases of KA, 37 of cSCC‐KAL (all considered follicular type) and 44 of SCC‐OTHER comprising 18 (41%) pure follicular, 15 (34%) hybrid follicular/surface neoplasms, five (11.4%) cSCC arising in Bowenoid actinic keratosis and six (13.6%) cSCC not otherwise specified. Clinical differences between KA, cSCC‐KAL and cSCC‐OTHER were found for median age (75, 81 and 81.5 years, respectively), head and neck location (20%, 86% and 84%, respectively) and duration < 5 months (95%, 63% and 36%, respectively). KA show a mosaic pattern for p16 (> 25–90% of neoplasm area) and a peripheral graded pattern for p53 (up to 50% moderate and strong nuclear staining) in 92% vs. 0% of cSCC‐KAL and 0% of cSCC‐OTHER. In contrast, a highly aberrant pattern (usually null) for one or both p16 and p53 was present in 0% of KA, 83.8% of cSCC‐KAL and 90.9% of cSCC‐OTHER. Abnormal distribution of Ki67 beyond the 1–3 peripheral cells was uncommon in KA (4.2%), and common in cSCC‐KAL (67.6%) and cSCC‐OTHER (88.4%). Our findings indicate that KA is clinicopathologically distinct from cSCC. The absence of highly aberrant protein expression patterns for two major tumour suppressor pathways (p16/CDNK2A and p53) and the regular peripheral Ki67 proliferation pattern in KA, compared with the prevalent aberrant patterns in cSCC, suggests that KA is a distinct entity from the malignant tumour pathway of cSCC. Combining the refined clinical, histological and immunohistochemistry features in our study should help to reduce the risk of diagnostic error and inform future studies to determine the molecular basis of KA.

Citation

Shpadaruk, V., Carr, R. A., Mesiano, D., Heffron, C., Radonic, T., Wiggins, J., Tso, S., Agrawal, R., Cheung, E., Slater, D., & Craig, P. (2022). CPC13: Comparative study of p16, p53 and Ki67 immunostaining indicates that keratoacanthoma and cutaneous squamous cell carcinoma are clinicopathologically distinct entities. British Journal of Dermatology, 187

DOI

10.1111/bjd.21113

URI

https://hdl.handle.net/20.500.14709/721