The primary cilium is a cell surface organelle that was discovered in the 1800s, but only in the last 20 years has been recognized for its importance in cellular biology.

The primary cilium has critical roles in signaling pathways such as Hedgehog (HH) and Wnt.

Basal cell carcinoma (BCC) depends on HH pathway activation through the primary cilium, which is the basis for the BCC therapies vismodegib and sonidegib.

Immunofluorescence staining of conventional melanocytic nevi, which retain primary cilia, and melanoma, which shows primary cilia loss, provides the basis for a novel diagnostic tool.