The research team, led by Dr. Lisa Bailey, a former president of the American Cancer Society's California Division and one of California's top breast surgeons, studied four young women - aged from 21 to 39 years old - with multifocal invasive breast cancer.

The researchers observed that all the patients developed tumors in areas of their breasts next to where they carried their cell phones, often for up to 10 hours per day, for several years. None of the patients had a family history of breast cancer. They all tested negative for BRCA1 and BRCA2 - breast cancer genes linked to about one-half of breast cancer cases - and they had no other known breast cancer risks.