The force of a pumping heart changes how cancer cells function, halting their ability to multiply and spread, a new study shows. The finding may help to explain why heart cancer is so rare, occurring in fewer than 2 in 100,000 people per year. In addition to offering a possible explanation for why heart cancer is so rare , the findings could open the door for new therapies for other cancers, researchers concluded in the study, which was published April 23 in the journal Science . We're going to "try to exploit this knowledge to develop a mechanical therapy for cancer," study author Serena Zacchigna , head of the Cardiovascular Biology Laboratory at the International Centre for Genetic Engineering and Biotechnology in Italy, told Live Science. Zacchigna and colleagues are developing bands that can be strapped around tumors on the skin and then reproduce the force of a beating heart.…