FBD (Fibrocystic Breast Disease) is typically associated with PMS and is regarded as a risk factor for breast cancer (although not as significant as other risk factors). FBD is characterized by cysts that are cyclic and bilateral, with multiple cysts of varying sizes that give the breast a nodular consistency. Pain or premenstrual breast pain and tenderness are common, although FBD can occur without symptoms. FBD occurs in 20-40% of premenopausal women.
FBD appears to be the result of an increased estrogen-to-progesterone ratio; however, other hormones may play a role.

Definitely avoid caffeine (coffee, tea, soft drinks, chocolate, caffeinated medications), which can elevate levels of compounds that
promote overproduction of cellular products within breast tissue (i.e. fibrous tissue and cyst fluid).

It is also important to make sure the colon and liver are functioning adequately. FBD has been linked to constipation and a low fiber diet. Likewise, the liver is the primary site for estrogen clearance, and it requires sufficient levels of B-vitamins to do its job.

Iodine deficiency and/or subclinical hypothyroidism may be a causative factor in FBD.

Supplements to consider:

Vitamin E has been shown to relieve many PMS symptoms, particularly FBD, in several double-blind clinical studies.

Vitamin B-complex (to aid liver function)

Colon- and liver-cleansing herbs (NSP's Chinese Tiao He Cleanse contains both)

Herbs rich in iodine (such as NSP's Thyroid Activator)

Additional information can be found in:

Herb Allure Resource Toolkit (HART Toolkit)
Encyclopedia of Natural Medicine, 2nd ed.