"However, while about 90 percent of North American women have fibrocystic disease, about 40 percent of these women experience no symptoms. Their breasts may be normal to examination, but the disease may be only microscopically detectable with a biopsy.
"Enough iodine enables the excess cells to be cleared out, and the breast can return to its normal resting state as the fibrocystic disease slowly disappears from the breast.
"Fibrocystic disease over decades of hormonal stimulation eventually tends to cause some cells to change to cancer cells. Lack of iodine causes fibrocystic disease, so women who have fibrocystic disease are susceptible to breast cancer. Although breast scars from fluid leakage out of the cysts are often permanent, iodine given therapeutically in the correct doses gradually gets rid of all fibrocystic disease except for the scars. Rest of the story:
Derry. Iodine and the Breast -- Research