How can cancer preventing genes from animals be transferred to humans?
While this research is interesting and might help curing cancer at some point, it's not a ground breaking revelation.

The gene in question here is TP53, coding for the very-well known tumor supressor protein p53. Humans do have this gene, but apparently elephants hav acquired multiple copies of it (~20) during evolution and that might explain why they don't get cancer so easily.

The problem of testing this is not a technical one. Using modern genetic engineering methods it should be fairly easy to multiply the gene in human or mice embryos, or introduce the additional variants from the elephants. Someone might already be planning to do that in mice.

For use on humans however, this is highly unethical. Without proof that these gene copies actually prevent cancer (and one observational study is not a proof), you can't just use a new medical treatment. Secondly this treatment would require genetic modification of an embryo (because its actually cancer prevention, not acute treatment) and that is illegal almost everywhere on earth (even genetic modification of somatic tissue for cancer treatment is just now becoming an experimental therapy).