How nucleotide excision repair protects against cancer

Eukaryotic cells can repair many types of DNA damage. Among the known DNA repair processes in humans, one type - nucleotide excision repair (NER) - specifically protects against mutations caused indirectly by environmental carcinogens. Humans with a hereditary defect in NER suffer from xeroderma pigmentosum and have a marked predisposition to skin cancer caused by sunlight exposure. How does NER protect against skin cancer and possibly other types of environmentally induced cancer in humans?.