Thickness of superficial basal cell carcinoma (sBCC) predicts imiquimod efficacy: A proposal for a thickness-based definition of sBCC

Background Basal cell carcinoma (BCC) is the most common malignancy in the white population. It is an important driver of healthcare costs and causes significant morbidity. Topical imiquimod is a good noninvasive treatment alternative for surgical excision in superficial BCC (sBCC). However, there are currently no uniform histological definitions of sBCC. A definition based on tumour thickness might be a good alternative. Objectives To determine whether tumour thickness in sBCC is a predictor of treatment failure. Methods We retrospectively examined 127 histological biopsy specimens of sBCC treated primarily with imiquimod five times a week for 6 weeks. Mean follow-up was 34 months (range 3-91). Recurrence was evaluated clinically with histological verification. Results Among nonrecurrent cases the median tumour thickness was 0·26 mm (range 0·09-0·61), while for recurrent cases the median tumour thickness was 0·57 mm (range 0·41-1·41, P < 0·0001). Among lesions ≤ 0·40 mm in thickness, none recurred, whereas for lesions > 0·40 mm the recurrence rate was 58% (P < 0·0001). Conclusions We recommend the use of tumour thickness to define the superficial pattern in pathology reports for BCC as this can help to determine treatment response of sBCC to imiquimod. What's already known about this topic? Topical imiquimod is a noninvasive treatment modality for primary, histologically proven superficial basal cell carcinoma (sBCC), sparing patients a surgical excision. Current definitions of histological sBCC vary and are imprecise. What does this study add? Superficial basal cell carcinoma thickness is a predictor of treatment failure in imiquimod therapy. Histological definition of sBCC based on tumour thickness is more precise than current definitions.