Skin, Seborrheic keratosis

Seborrheic keratosis (SK) is a common diagnosis, and it exists in many forms. This example is a commonly encountered form of SK, with an exophytic pattern, showing keratin-filled “horn” cysts.

While it is a benign entity, activating mutations in FGFR3 have been found in many sporadic lesions and are thought to drive proliferation (Hafner et al. Modern Pathology (2007) 20, 895–903). Malignant tumours developing within SK is seen in extremely rare cases, and most cases reported were cases of basal cell carcinoma (BCC). The exact relationship between SK and BCC is unclear.

See related contents for references:

1) Hafner et al. Modern Pathology (2007) 20, 895–903