Tomatoes (Solanum lycopersicum) are a rich source of the carotenoids beta-carotene and lycopene, and a fairly good source of alpha-tomatine and melatonin, all of which have been found to have anti-cancer activities. Tomatoes also contain some lupeol and naringenin. Tomatoes have antioxidant and anti-inflammatory properties.
Increased intake of tomatoes is associated with decreased cardiovascular disease and reduced risk of heart attack. Tomato consumption has been found to be associated with reduced risks of cancer of the mouth, breast, lung, stomach, pancreas, prostate, colon, ovary, and endometrium.

Breast cancer-related effects of eating tomatoes

Tomatoes and tomato compounds have been reported to prevent or inhibit breast cancer or its progression in numerous studies. Tomato compounds have also been shown to enhance treatment with Adriamycin (doxorubicin) and reduce multidrug resistance in cancer cells.

Breast cancer risk

A number of studies have found an inverse association between breast cancer risk and increasing consumption of tomatoes, components of tomatoes, or vegetables such as tomatoes that have high levels of carotenoids.
One study of 84,805 postmenopausal women in the Women's Health Initiative Observational Study found that dietary beta-carotene and lycopene were both inversely associated with the risk of hormone receptor positive (ER+/PR+) breast cancer.
A meta-analysis of data from previous prospective studies reported that women in the top fifth (quintile) of total circulating carotenoids had a 19% lower risk of breast cancer compared to those in the lowest fifth. When carotenoids were considered individually, women in the top quintile of lycopene were found to have a 22% lower risk of breast cancer than those in the bottom quintile. However, not studies have reported an inverse association between lycopene and breast cancer risk. One large study found no association between dietary or plasma lycopene levels and the risk of breast cancer in middle-aged and older women.

Specific chemopreventive actions of tomato components

A Scandinavian study found that dietary (but not supplemental) beta-carotene had a protective effect against lobular breast cancer in postmenopausal women. Another European study reported that high intake of beta-carotene was protective against breast cancer in postmenopausal women using hormone replacement therapy (HRT). The same study also found that dietary beta-carotene was associated with lowered risk of breast cancer in postmenopausal women with relatively high alcohol consumption.
Dietary carotenoids have been found to inhibit the cancer-promoting effects of both estradiol and genistein (a phytoestrogen found in soy), thereby reducing their harmful effects in hormone-dependent breast cancer.
As noted above, tomatoes are a dietary source of melatonin. Melatonin reduces aromatase activity within the breast, thereby decreasing estrogen production and protecting against ER+ breast cancer. Melatonin has also been found to reduce triple negative (ER-/PR-/HER2-) breast cancer growth, proliferation and migration in cell and animal studies.
Studies of naringenin, a tomato flavanone, have shown that it also inhibits ER+ breast cancer cell growth and migration in the presence of estradiol.

Breast cancer treatment

One study reported that beta-carotene enhanced the cytotoxicity of Adriamycin in both ER+/PR+ and triple negative breast cancer cells. Beta-carotene has also been demonstrated to reduce multidrug resistance in cancer cells.
Several studies have shown that the cardioprotective effect of tomatoes and lycopene extends to reducing the cardiotoxicity of Adriamycin chemotherapy by protecting against heart cell injury.

Breast cancer survival

Several studies of early stage breast cancer patients have reported that higher levels of cartenoids and/or retinol (a form of vitamin A that is a by-product of beta-carotene in the body) in the blood are associated with lower risks of both breast cancer recurrence and diagnosis of a new primary breast tumor. For example, one study found that higher plasma levels of retinol were associated with increased breast cancer survival in postmenopausal women.

Additional comments

Cherry tomatoes rank the highest of all tomatoes in lycopene and overall antioxidant content, presumably because of their high ratio of tomato skin to tomato flesh and rich color. Frying greatly reduces the lycopene content of fresh tomatoes. However, lycopene is absorbed in greater quantities from cooked tomatoes than fresh tomatoes. The best sources of bioavailable lycopene are tomato paste and tomato sauce.
While tomato ketchup has a relatively low overall carotenoid content compared to fresh tomatoes or tomato sauce, it is a good source of lycopene. However, note that high fructose corn syrup is the second most abundant ingredient in regular ketchup (sugar-free versions are available).
Non-organic tomatoes must be washed very thoroughly to remove pesticide residue.

Sun-dried tomatoes have high copper content

Sun-dried tomatoes contain relatively high levels of copper (approximately 0.42 mg per ounce), which could contribute to angiogenesis and metastasis of breast cancer. While copper is a vital nutrient, women with breast cancer probably should not exceed the RDA (recommended daily allowance) of approximately 0.9 mg.

Tomato soup can be a source of harmful compounds

Ready-made tomato soup can have a high level of sodium nitrite, a known carcinogen. Check the labels of canned or otherwise pre-made soups and avoid those containing sodium nitrite and other sodium compounds. The salt content of such soups can also be acceptably high for those who must limit their sodium intake. Canned tomato soup can also be a source of bisphenol A (BPA), a breast carcinogen that is often used in interior can coatings to prevent corrosion.

Carotenoid supplements are not recommended

Beta carotene, vitamin A and lycopene should be obtained from food rather than supplements. Generally speaking, synergistic interactions between the biologically active components in a given fruit or vegetable are important to its potential health-related characteristics. Supplementation by beta-carotene and lycopene both have been found to be ineffective in reducing the risk of breast cancer. In addition, beta-carotene supplementation has been linked to increased risk of lung cancer in high-risk persons and high serum beta-carotene concentrations (presumably also resulting from supplementation) have been associated with increased risk of aggressive prostate cancer.

Sources of information provided in this webpage

The information above, which is updated continually as new research becomes available, has been developed based solely on the results of academic studies. Clicking on any of the underlined terms will take you to its tag or webpage, which contain more extensive information.
Below are links to 20 recent studies concerning this food and its components. For a more complete list, including less recent studies, please click on tomatoes.