Less than 1 percent of cancers start in the heart, and disease that begins elsewhere seldom spreads to the blood-pumping organ. New research suggests mechanical force might have a protective role Lung cancer cells, shown in green, growing in a mouse heart ICGEB Cancer can occur anywhere in the human body, but it’s rarely found in the heart—a conundrum that has long stumped scientists. Now, a new study in mice may have figured out why: The mechanical force of a beating heart seems to create an environment that’s inhospitable to cancer. The findings, published April 23 in the journal  Science , could help researchers develop new therapies for the disease that rely on mechanical stimulation. The American Cancer Society estimates that more than  two million cancer cases will be diagnosed in the United States this year, but less than 1 percent of them will be cancers of soft tissues, including the heart.…