Anti-Breast Cancer Activity of a Papaya

The papaya fruit is a excellent fruit that has many food applications.  Like many plants, both the fruit and other parts (seeds, leaves, etc.) of the papaya tree have been used for various medicinal purposes.  Papain is probably the best known component of papaya and is commonly used topically for the relief of rashes, stings, and burns.

New cancer research has examined the effects of a papaya leaf extract on several cancer cell lines, including breast cancer cells.  For this study, MCF-7 breast cancer cells were grown in a cell culture system and treated with different amounts of the papaya leaf extract.  In addition to the effects on the breast cancer cells, the investigators examined the effects of the papaya leaf extract on a type of white blood cell to determine how the papaya leaf extract might function.  The investigators reported that:

  • The papaya leaf extract prevented the growth of breast cancer cells in culture with higher doses having a greater benefit.
  • Prevention of cell growth appears to be mediated, at least in part, by stimulating the programmed cell death of the breast cancer cells.
  • The papaya leaf extract suppressed the production on inflammatory chemicals from the white blood cells.
  • Production of chemicals with possible anti-cancer properties were increased when white blood cells were treated with the papaya leaf extract.
  • None of the doses of the papaya leaf extract appeared to have any damaging effects normal cells.

These are very positive research results that suggest possible anti-cancer benefits of a papaya leaf extract.  While this study was not dedicated to just breast cancer, parts of the study were done using breast cancer cells and the anti-tumor effects were noted in these cells as well as the other types of cancer cells.  Overall, this study suggests that a papaya leaf extract inhibits breast cancer cell growth and alters the immune system in an anti-cancer direction.  Additional research will need to be done to determine the active component(s) of the papaya leaf extract, to discover how it functions in breast cancer cells, and to determine if these benefits translate to people.  Nonetheless, this study showed good initial results and makes a great starting point to further examine the benefits of papaya for breast cancer.  Since it is unknown what the active component was in this study, it is also unknown if the active ingredient is present in the papaya fruit as well.  However, the papaya is an excellent food choice as it is very low in saturated fat, cholesterol, and sodium and is a good source of dietary fiber, vitamin A, vitamin C, and folate.

Studies have not established the effect of papaya on breast cancer

Papayas (Carica papaya) and their seeds contain substances that have been shown to have antihypertensive, antioxidant, anti-amoebic, antiparasitic, antiseptic, wound and burn healing, contraceptive and neuroprotective properties, as well as improving cholesterol profile and assisting with digestion. Papaya is a good dietary source of vitamin C and vitamin A (through its beta-carotene content). The fruit has been selected to raise levels of vitamin A in children in deficiency-prone countries such as Cameroon and Sri Lanka. Compounds with known cancer-fighting properties found in papayas include carotenoids such as lycopene, beta-carotene and cryptoxanthin, as well as several isothiocyanates. The benzyl isothiocyanate found in papaya has been shown to induce apoptosis in pancreas, prostate, and leukemic cancer cells and to inhibit carcinogen-induced bladder cancer.

Breast cancer-related effects of eating papaya

Benzyl isothiocyanate, found in papaya flesh and seeds, has been shown to selectively induce apoptosis in human breast cancer cells. The high carotenoid levels found in papayas suggest that consuming the fruit could serve to protect against breast cancer. However, no population studies have been performed that directly assess the effects of papaya on the risk of breast cancer.

Additional comments

Papayas are sometimes referred to as paw paws, but the paw paw (Asiminia triloba) sold in the U.S. is a different fruit. Papayas have two possible flesh colors, yellow and red. The red color of red papaya fruit is due to an accumulation of lycopene; the yellow color of yellow papaya is the result of conversion of lycopene to beta-carotene and beta-cryptoxanthin. Papayas should be eaten ripe, without the skin or seeds. Even though the peel is not eaten, papayas should be washed thoroughly before being cut up for consumption since potent pesticides typically are used in growing them.

Both raw and cooked green papayas (i.e., unripe papayas) are used in some Asian cuisines. For example, atchara, a Filipino condiment or side dish, is made of primarily of pickled raw green papaya. Ground papaya seeds are used in some cuisines similarly to black pepper. However, we recommend against consuming green papaya (whether raw, cooked or dried) or papaya seeds. Unlike ripe papaya, green papaya contains a high concentration of a type of latex that has been shown to produce uterine contractions in rats; this may be the basis for the belief in parts of Asia that consumption of papaya is unsafe during pregnancy. In fact, green papaya is used for female contraception and abortion in some traditional medicine systems.

Papaya seeds contain a higher proportion of benzyl isothiocyanate than does the flesh and they are sometimes used as part of herbal preparations. However, one study found that rats consuming papaya seed extract exhibited liver cell damage and precancerous liver changes in a dose-dependent manner. Another study found that benzyl isothiocyanate promoted urinary bladder carcinogenesis in rats. Papaya seed extracts also have been shown to have dose-dependent spermicidal effects, causing human sperm immobilization and death.

Dried papaya typically has been treated with sulfur dioxide to prevent the fruit from oxidizing during and after the drying process, thereby preserving its color. However, sulfur dioxide and its derivatives have been shown to increase the frequencies of chromosomal aberrations in mammalian cells and cause oxidative damage in multiple organs of male and female mice. Therefore, we recommend obtaining unsulfured dried fruit where possible.

Papain, a component of papaya found in some powdered meat tenderizers and some herbal supplements, has been shown to increase the effect of warfarin (coumadin) blood thinning therapy.

Note that while we are continually searching for new evidence specifically concerning this food, there is not much interest in it among breast cancer researchers, so few studies are available.