In simplest terms, curcumin, piperine, sulforaphane, indole-3-carbinol, and quercetin are some of the most common food nutrients that have been shown to be active in preventing or stopping breast cancer growth. (Review article: Chemoprevention of Breast Cancer With Vitamins and Micronutrients: A Concise Review)
Indole-3-carbinol (I3C) is found in abundance in brassica/cruciferous vegetables like broccoli. (Modulatory Effect of Indoles on the Expression of miRNAs Regulating G1/S Cell Cycle Phase in Breast Cancer Cells)
Sulforaphane has been found to stop cell reproduction and proliferation in breast cancer cells. (Suppression of microtubule dynamic instability and turnover in MCF7 breast cancer cells by sulforaphane)
Curcumin sources: turmeric
Piperine sources: black pepper
Sulforaphane sources: broccoli, brussels sprouts, cabbage, cauliflower, kale
Indole-3-carbinol sources: same as sulforaphane sources - broccoli, brussels sprouts, cabbage, cauliflower, kale
Quercetin food sources: capers, radish leaves, dill, cilantro, raw red onion, radicchio, red leaf lettuce, watercress, kale, etc.
Apigenin food sources: dried and fresh parsley (a LOT in here!), celery seed/heart/root, oregano, peppermint, juniper berries, kumquats, artichokes, Queen Anne's Lace leaves, vinespinach
Studies listed below show that general fruit and vegetable consumption are protective against breast cancer:
This 2020 meta-analysis stated that 7-8 servings of vegetables and fruits per day may provide the best nutrition for long-term survival in cancers, including breast cancer.
This 2019 meta-analysis stated that fruit, vegetables and soy intake were inversely correlated with breast cancer risk and suggested that these types of foods should be incorporated into the diet to prevent breast cancer.
This 1990 meta-analysis found that vitamin C had the strongest protective effect against breast cancer.
There are also studies on many specific substances from a variety of vegetables and fruits, such as apigenin, which acts on breast cancer as well as other cancer types: Apigenin role as cell-signaling pathways modulator: implications in cancer prevention and treatment ("Studies suggested that Apigenin has the potential to suppress multiple human cancers including prostate cancer, lung cancer, breast cancer, colorectal cancer, liver cancer, melanoma, glioblastoma, osteosarcoma, leukemia, ovarian cancer, pancreatic cancer and cervical cancer.")
Specific to breast cancer, this study found that apigenin was selectively toxic to breast cancer cells and inhibited aromatase: In vitro evaluation of estrogenic, antiestrogenic and antitumor effects of amentoflavone
There are many, many food sources of apigenin.
Nigella Sativa (black seed oil) found beneficial against breast as well as lung, ovarian and colorectal cancer.
Medicinal mushrooms significantly improved survival rates, alleviated side effects of standard oncological therapies, improved quality of life, and resulted in life prolongation in breast, as well as colorectal, lung, and other cancers.
There are also other substances that have been studied for breast cancer but they are not necessarily exclusive to breast cancer either.
Tunisian olive leaves - were found effective against breast cancer cells.
Oregano extracts and essential oil - showed activity against human breast cancer cells (there were no other types of cancer studied in this study).