Cytokeratins as Markers of Follicular Differentiation

The study investigated the expression of cytokeratins and hair keratins in trichoblastomas (TB) and nodular basal cell carcinomas (BCC) to understand their follicular differentiation. Both TB and BCC showed consistent expression of CK14 and CK17, with CK6hf present in all TB and 72% of BCC. CK15 was focally expressed in 38% of TB but absent in BCC, while CK19 was expressed in 70% of TB and 22% of BCC. CK8 was found in Merkel cells in all TB but not in BCC. No type I and II hair keratins were expressed in either tumor type. These findings suggested that both TB and BCC differentiated towards the outer root sheath epithelium or the companion layer, rather than the inner root sheath, matrix, or cortex.