Sometimes it takes darkness to see the light: Pitfalls in the interpretation of cell proliferation markers (Ki-67 and PCNA)

The degree of cell proliferation in a tumor is often associated with metastatic risk and mortality. Proliferating cell nuclear antigen (PCNA) and Ki-67 are proliferation markers that can be used to assess malignant potential in cutaneous lesions and pathological cell proliferation in psoriasis. These markers are elevated during periods of cell proliferation; however, they are also upregulated following UV irradiation. This up regulation may be problematic, as many skin lesions are subject to sun exposure in an everyday setting.