Although most viruses are considered enemies, scientists have engineered a herpes virus that could actually help treat patients suffering from cancer, according to Nature.

The United States has approved the drug Imlygic for "hard-to-treat" melanoma, after more than a century of scientific pondering on the correlation between cancers and viral infections.

The virus is engineered with a special gene that stimulates the immune system. It is injected directly into the tumor and, so far, about 16 percent of patients who used the drug saw shrinkage in their growths, compared to 2 percent in those who only relied on traditional medical treatments, according to the Wall Street Journal.

Researchers stressed that although the drug seemed to have some affect on cancerous growths, it had no affect on melanoma that managed to spread into lungs, internal organs and the brain.

"I expect to see a great deal happening over the next few years," said Stephen Russell, a cancer researcher at the Mayo Clinic in Minnesota.

Depending on the treatment's duration, one course is estimated to cost around $65,000, according to CBS News.

Melanoma is among the deadliest forms of skin cancer and affects an estimated 74,000 Americans.