Mini MCAT passage: Skin cancer prevention

Skin cancer is the most common cause of cancer in the United States. Many forms of sunscreen help prevent against UV-B radiation which has been linked to basal and squamous cell carcinoma, which each arises from keratinocytes but in different levels and stages of development within the epidermis. Most sunscreens, however, notably lack any protection from UV-A radiation which is known to cause a more severe form of skin cancer known as malignant melanoma. Zinc oxide based compounds have shown efficacy at repelling UV-A radiation, thus decreasing the risk of malignant melanoma.

One dermatologist is in the process of developing a new form of sunscreen that incorporates zinc oxide to protect against UV-A and UV-B radiation. She has designed an experiment where half of the subjects apply her novel sunscreen while the other half apply standard sunscreen every day for four and a half years. Following the study, she finds that $2\mathrm{\%}$‍ of the subjects applying her novel sunscreen developed malignant melanoma while the occurrence was $8\mathrm{\%}$‍ in those applying the standard sunscreen.