Follicular cutaneous squamous cell carcinoma: an under‐recognized neoplasm arising from hair appendage structures

Summary Background Cutaneous squamous cell carcinoma ( SCC ) with no demonstrable point of epidermal origin is problematic as it raises consideration of metastatic SCC histologically. There are rare case reports and series of SCC arising from the wall of hair follicle structures. Such lesions have been termed follicular SCC ( FSCC ). Objectives To investigate the clinicopathological features of FSCC . Methods We prospectively collected cases of follicular SCC over a 5‐year period. Follicular SCC is defined as a cutaneous SCC deriving from a pre‐existing hair follicle structure. Lesions were considered to represent ‘hybrid’ SCC s if an interfollicular epidermal origin was also demonstrated; SCC s with > 50% of the origin from interfollicular epidermis were excluded. Histological features and clinical information were evaluated. Results We identified 61 cases of follicular SCC arising in 60 patients from a database of 5212 cutaneous SCC s encountered over the same time period by the same authors. There were 49 pure follicular SCC s and 12 hybrid lesions. The male to female ratio was 44 : 16; the mean age was 74 years (range 44–93). Follicular SCC represents 1·2% of all primary SCC s. Biopsies of such lesions, if the appendage structure of origin is not represented, are histologically indistinguishable from metastatic SCC . Conclusions Recognition of this under‐reported form of SCC is essential if an inappropriate diagnosis of metastatic SCC , with potentially harmful and inappropriate therapy and investigation, is to be avoided.