Garlic, onions and other members of the allium genus, such as leeks, chives, scallions and shallots, have been shown to have antimicrobial, radioprotective, antithrombotic, hypolipidaemic, anti-inflammatory, antiarthritic and hypoglycemic effects, as well as improving immune function.
Epidemiological studies have demonstrated an association between increased consumption of allium vegetables and a reduction in many different types of cancer, including cancer of the breast, prostate, lung, endometrium, stomach, colon, bladder, esophagus, larynx, mouth, ovary, and liver, as well as melanoma, acute myeloid leukemia, and childhood acute leukemia.
Garlic contains various substances reported to have anti-breast cancer effects, including ajoene, apigenin, enterolactone, allicin and the related compounds diallyl disulfide and diallyl trisulfide.

Breast cancer-related effects of eating garlic

Epidemiological studies

One large European study found that eating onions and garlic was associated with lower risk of breast cancer. Another large Italian population study found a relationship between the consumption of increasing intake of flavones and flavonols found in allium vegetables and a reduction in the risk of breast cancer. A Korean study found an association between onion and garlic consumption and lower incidence of breast cancer.

Raw garlic

Numerous studies have shown that garlic and its components inhibit proliferation, reduce migration and invasiveness, and induce apoptosis of cultured human breast cancer cells. Garlic has been shown to decrease DNA strand breaks induced by carcinogens, inhibit DNA and RNA synthesis and protein folding in breast cancer cells, retard the growth of breast cancer cells by causing cell cycle arrest and apoptosis, and suppress angiogenesis. Garlic has also been demonstrated to have protective effects against Adriamycin-induced heart damage.

Organosulfur compounds

The anti-carcinogenic effects of allium vegetables such as garlic are attributed in part to organosulfur compounds (ajoene, diallyl sulfide, diallyl disulfide, diallyl trisulfide, diallyltetrasulfide, dipropyltetrasulfide, among others). Ajoene has been demonstrated to interfere with protein folding in triple negative breast cancer cells, which in turn causes their death.
Diallyl disulfide has been shown to decrease carcinogen-induced cancers in experimental animals. Diallyl disulfide has also been demonstrated to induce apoptosis (programmed cell death) in hormone receptor positive (ER+/PR+) breast cancer cells. Diallyl trisulfide has been shown to suppress breast cancer cell invasion and metastasis, thereby delaying the onset or progression of breast cancer. Diallyl trisulfide has also been found to inhibit triple negative breast cancer cell proliferation and metastasis.

Apigenin

Garlic is a good source of the flavone apigenin, which has been found to induce apoptosis across a variety of breast cancer cell lines. For example, apigenin has been shown to exhibit potent growth-inhibitory effects in HER2+ breast cancer cells. Apigenin has also been shown to inhibit the growth of patient-derived triple negative (ER-/PR-/HER2-) organoids and sensitize triple negative cells to Adriamycin chemotherapy. In addition, apigenin has been shown to lessen Adriamycin-induced kidney damage without reducing its cytotoxic effects against tumor cells in a mouse model of breast cancer.

Enterolactone

Postmenopausal women with breast cancer and a high intake of the lignan enterolactone have been found to be less likely to die from their breast cancer than those with a low intake. Enterolactone has also been found to increase the sensitivity of breast cancer cells to radiation, thereby potentially enhancing the treatment effects of radiotherapy.

Garlic supplements can interfere with chemotherapy

Garlic supplements have been shown to reduce the clearance of the chemotherapy drug Taxotere in some women, a result that is likely also to hold for Taxol. Garlic supplements have also been shown to interfere with the activities of platinum-based chemotherapy drugs such as cisplatin.

Additional comments

Organosulfur compounds are generated upon cutting or chewing garlic. Although some of the anticancer benefits of garlic are retained after cooking or processing it, raw garlic appears to have the most benefits. Raw and processed garlic should both be purchased organically grown.
Below are links to recent studies concerning garlic. For a more complete list, please click on garlic.