These patients have tumors with a mutation in a growth-promoting gene called kras that may render the drugs ineffective.

FORBES: ImClone's Gene Test Battle

In 2002 gene researchers in the U.K. discovered that two-thirds of melanomas have a mutation in a growth-promoting gene inside skin cells called BRAF.

FORBES: Targeting Melanoma

But the gene scan found the tumor was making large amounts of a growth-promoting protein called RET.

FORBES: Health