WSJournal #4. Letting Your Body Fight Cancer.

WSJournal #4. Letting Your Body Fight Cancer.

Few advances in cancer care are generating more enthusiasm than harnessing the power of the immune system to fight the disease.

Tom Stutz is one reason why. Last April, the 72-year-old retired lawyer was confined to a wheelchair, struggling for every breath, and required help with simple tasks such as eating, all because of a previously diagnosed skin cancer that had spread to his lungs and liver. "I was ready to check out, to be honest," he says.

That month, he began taking an experimental drug known as MK3475. Six weeks later, he started feeling better. Today, Mr. Stutz has jettisoned the wheelchair and regularly walks a 3.5-mile loop near his home in Los Angeles. "I feel terrific," says Mr. Stutz, who learned after a checkup in the fall that his tumors had shrunk by about 65% so far.

For decades, cancer researchers have wondered why the immune system typically doesn't treat tumor cells as invaders and target them. Part of the mystery was recently solved: Tumors protect themselves by hijacking the body's natural brake for the immune system.

MK3475, being developed by Merck & Co., is among a new category of drugs that release the brake, unleashing an army of immune cells to hunt down the cancer. A recent report from a trial in which Mr. Stutz participated said that of 85 patients who took the drug, 51% saw their tumors significantly shrink; in eight cases, the tumors couldn't be detected on imaging tests.

Still, not everyone was helped. And unleashing the immune system can put normal cells in harm's way: In studies of MK3745 and similar drugs, some patients developed serious side effects related to immune-system response, including a small number who died.

But interest in the approach is strong. Bristol-Myers Squibb Corp.'s BMY -0.75% drug Yervoy, approved by the Food and Drug Administration in 2011, is the first of its kind to reach the market. The company has others in development. GlaxoSmithKline GSK.LN -0.22% PLC and AstraZeneca 's AZN.LN -0.46% MedImmune are among others exploring ways to activate the immune system against cancer.

One reason for the excitement is that most "solid" tumors—colon, lung, breast, prostate—use the same or a similar mechanism to hide from the immune system. Obstructing that mechanism may have a broad impact across a variety of malignancies.