Morphological and immunohistochemical analysis of basal growth patterns of actinic keratoses in the marginal area of keratoacanthomas

Abstract

In recent years, with the rising incidence of non-melanoma skin cancers, increasing attention has been paid to the characterization of cutaneous tumors. Within this context, squamous cell carcinoma (SCC) and its precursors have become a key focus, particularly regarding their progression pathways. Keratoacanthoma (KA), a tumor that resembles SCC clinically and histologically but generally follows a more benign course, remains less well characterized. <br/> The aim of this study was to investigate the histological features of KA and its surrounding microenvironment in order to evaluate potential equivalence with SCC. The working hypothesis was that if the origin tissue of both tumors shares similar characteristics, then KA and SCC might represent two forms of the same disease spectrum. <br/> We analyzed 198 cases of histologically confirmed KA, assessing demographic patterns, lesion localization, and histological parameters such as AK/KIN and PRO grading, solar elastosis, and hyperkeratosis. Notably, we observed a significant correlation between AK/KIN and PRO grading, with AK 1 and PRO 1 as the most frequent findings, suggesting the predominance of early proliferative stages. Our findings align with those of the preexisting literature regarding SCC, particularly in recognizing AK 1 as a critical stage in the development of KA as well. The high incidence of KA in sun-exposed areas, together with the presence of significant solar elastosis and basal proliferation patterns, further supports the role of chronic photodamage in KA pathogenesis. Age- and sex-dependent variations were identified in PRO grading, while solar elastosis and hyperkeratosis showed no significant sex-based differences. These findings highlight the importance of age, location, and histological features in managing KA. <br/> Our findings support the idea that KA shares key histological features with SCC, particularly in the pattern of basal proliferation. If confirmed in future research, this could support the interpretation of KA as a variant of SCC rather than a distinct entity. This has implications for diagnosis and management. <br/> This thesis is structured to first describe the study population and anatomical localization of lesions, followed by a detailed analysis of histological parameters, age and sex stratification, and correlations between proliferative markers.