Margin involvement and clinical pattern of basal cell carcinoma with mixed histology

Background Mixed basal cell carcinoma (BCC) has not been sufficiently and specifically studied. Objective The aim of this study was to estimate in adults the prevalence of mixed cases observed among primary BCCs and to compare clinical and anatomical features of mixed vs. single BCCs, with focus on the incomplete excision. Patients and methods A total of 3636 histologically confirmed primary BCCs were examined. Data on gender, age, histological subtype, anatomical location and margin involvement were collected. Mixed type was defined as a combination of two or more single subtypes. Results Prevalence of single and mixed BCCs was 82.2% and 17.8% respectively. Prevalence of BCCs on the upper limbs was higher in mixed than single cases (8.8% vs. 4.0%; P <0.001) while prevalence on the back was lower (16.9% vs. 23.7%; P <0.001). Tumour was aggressive in 59.1% of mixed vs. 16.0% of single BCCs (P <0.001). Margin involvement was more prevalent in mixed than in single BCCs (16.7% vs. 9.6%; P <0.0001). At multivariate analysis being mixed vs. single BCC was associated with aggressiveness of tumour (OR = 8.5, 95% CI, 6.9-10.4), lateral margin involvement (OR = 1.98, 95% CI, 1.42-2.76) and subject being man (OR = 1.31, 95% CI, 1.10-1.60) but not with deep involvement of margin or anatomical location. Conclusion Among BCCs, the mixed type may be observed in adults with relatively high rate and may represent a complex and individual subset of BCCs with potential aggressive behaviour.