As scary as it may sound, it's generally acknowledged that about 1 in 8 women will be diagnosed with breast cancer at some point in their lives. Two-thirds of these women develop the disease after age 50, so it's little wonder that younger women often don't think the disease poses a threat to them. The truth, though, is that 5% to 7% of all breast cancer cases occur in women younger than 40. For example, 36-year-old actress, Christina Applegate, underwent a double mastectomy to treat her breast cancer, while singer Kylie Minogue, also 36 at the time, underwent surgery, radiation, and chemotherapy. Younger women like Applegate and Minogue often have one or more risk factors for the disease, such as having a mother, sister, or daughter with breast cancer. In truth, this element alone makes a woman two to three times more likely to develop the disease. Likewise, breast cancer may be triggered by a genetic defect on one of two genes, called BRCA1 and BRCA 2. On estimation, one in 200 women carries these genes, and that increases their lifetime breast cancer risk to between 56% and 85%. Women who have received radiation therapy to the chest before the age of 40 are also more likely to develop breast cancer, as are those with a personal history of breast cancer or other breast diseases. Lifestyle factors, like being obese and drinking heavily, may also play a role in the early development of breast cancer. Some studies indicate that women who use oral contraceptives may be at slightly higher risk of developing breast cancer. But contradicting research on the Pill's relationship to breast cancer exists, meaning that studies are ongoing. Whatever the cause of breast cancer, it can be much harder to detect in women under 40. That's because younger breast tissue is naturally denser, making tumors harder to feel. Plus, many young women ignore the warning signs they do notice, believing that breast cancer just can't happen to them. The takeaway here is that early detection and prompt treatment of breast cancer can lead to a 98% chance of survival. For this reason, if you're under 40 and concerned that you are at risk - like all women, you should be vigilant about your breast health and communicate all concerns with your doctor.