(Undated) -- Scientists say they've developed a drug that helps the body successfully fight cancer naturally. The so-called delta inhibitor drugs that have proven successful in treating leukemia are also effective in lab tests against cancers of the lungs, pancreas, skin and breasts. Researchers say they're probably also effective against many other forms of the disease. The scientists say an added benefit is that once the body learns to fight off a cancer, it develops an immunity so the disease can never return. The study is published in the journal "Nature."