Bananas are a good dietary source of manganese, vitamin B6 and fiber. Bananas have anti-inflammatory, antimicrobial, neuroprotective and antioxidant activities. Bananas also have been shown to reduce blood pressure and the risk of coronary heart disease. Bananas appear to protect the stomach lining against acid and ulcers.
Bananas also contain modest amounts of several compounds with known anti-cancer activities, including alpha-carotene, beta-carotene, melatonin, and dopamine. Components of bananas have been shown to inhibit proliferation of leukemia and liver cancer cells in the laboratory.
Mice fed bananas were found to have reduced development of malignant ascites induced by Erhlich carcinoma cells. Consumption of bananas has been found to be associated with reduced risks of childhood leukemia, glioma (a type of brain cancer), renal cell carcinoma, as well as oral, esophageal and colorectal cancer.

Breast cancer-related effects of eating bananas

The anticancer activities of bananas do not appear to be primarily due to antioxidant components since bananas have among the lowest levels of antioxidant activity of any fruit as measured by traditional methods. However, it is evident that bananas do not promote cancer and could have anti-cancer properties. One 2009 study of Chinese women found that banana consumption was associated with lower risk of breast cancer. A large 2016 U.S. prospective study reported that adolescents with high banana intake had reduced risk of breast cancer in adulthood.

Additional comments

Like plantains, unripe or green bananas must be cooked, whereas ripe common (or sweet) bananas usually are eaten raw.
Note that while we are continually searching for new evidence concerning this food, there is not much interest in it among cancer researchers so few recent studies are available.