Skin cancer carries a lifetime risk nearly equal to that of all other cancers combined. Fo...

Skin cancer carries a lifetime risk nearly equal to that of all other cancers combined. Following is a graph (modified from Kraemer, 1997. Proc. Natl. Acad. Sci. (USA) 94: 11–14) depicting the age of onset of skin cancers in patients with or without XP, where the cumulative percentage of skin cancer is plotted against age. The non-XP curve is based on 29,757 cancers surveyed by the National Cancer Institute, and the curve representing those with XP is based on 63 skin cancers from the Xeroderma Pigmentosum Registry.

(a) Provide an overview of the information contained in the graph.

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(b) Explain why individuals with XP show such an early age of onset.