A recent study from the NEJM suggests that not all "benign" breast disease are Equal:

Researchers have learned not all benign tumors are created equal. Some are merely an overgrowth of normal cells, called a proliferative lesion. But sometimes these cells take on strange shapes. This condition, called atypia, is often a precursor to cancer.

The new study found that women whose benign lump showed signs of proliferation and atypia were about 400 percent more likely to develop breast cancer in their lifetimes.

While these numbers sound scary, Dr. Marisa Weiss, who founded breastcancer.org, cautions against overreacting. For instance, Weiss explained that if you had a 1 percent chance of developing breast cancer and that chance rose by 400 percent, you would now only have a 4 percent chance of getting the disease.

So when studies say that having a benign lump increases your risk by 50 percent, Weiss says women have to think through the numbers carefully. "Yes, your risk increases by 50 percent. But that doesn't mean that your risk [of getting cancer] is 50 percent."

(Kagan, "Breast Cancer Study Finds All Lumps Aren't Created Equal", ABC News, Jul.21; Hartmann et al., "Benign Breast Disease and the Risk of Breast Cancer", NEJM, Jul.21)