Metatypical Basal Cell Carcinoma: A Nine-Year Retrospective Cohort Analysis in the Context of the COVID-19 Pandemic

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Abstract
Background/Objectives: Metatypical basal cell carcinoma (MTBCC) is a rare and aggressive variant of non-melanoma skin cancer (NMSC) characterised by overlapping histological features of basal cell carcinoma (BCC) and cutaneous squamous cell carcinoma (cSCC). Owing to its increased propensity for local invasion, recurrence, and metastasis, MTBCC poses diagnostic and therapeutic challenges. This study aimed to characterise the epidemiological, histopathological, and clinical features of MTBCC and to evaluate temporal changes in tumour characteristics and aggressiveness before, during, and after the COVID-19 pandemic. Methods: A retrospective cohort study was conducted on 129 histologically confirmed MTBCC lesions diagnosed in the Pathology Department of the Mures Clinical County Hospital, Targu Mures, Romania, between January 2017 and December 2025. Demographic data, tumour location, histological subtypes, differentiation of the squamous component, aggressiveness parameters, and volumetric measurements of tumours and excision specimens were analysed. Volumetric analyses were restricted to cases with complete three-dimensional measurements. Statistical comparisons were performed across demographic variables and the following three time periods: pre-pandemic, pandemic, and post-pandemic. Results: The median age at diagnosis was 71 years, with a slight male predominance (p = 0.25) and a significant predominance of patients from urban areas (p < 0.001). Most tumours were located in the head and neck region. Mixed-type MTBCC was significantly associated with higher tumour aggressiveness (p = 0.0019) and with high-risk histological subtypes, particularly micronodular and adenoid–cystic variants. Tumour volume showed a significant inverse correlation with year of diagnosis (p = 0.0139; r = (−) 0.50), whereas excision specimen volume differed significantly according to year of diagnosis (p = 0.0425). Neither tumour volume nor excision specimen volume was associated with histopathological aggressiveness. Conclusions: Metatypical basal cell carcinoma is a rare skin malignancy in which biological behaviour appears to be determined primarily by histopathological architecture rather than tumour size. Mixed-type lesions were associated with significantly higher aggressiveness, underscoring the need for accurate histopathological assessment. These findings support a pathology-driven approach to management and emphasise the importance of adequate surgical treatment and long-term follow-up in patients with MTBCC.

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