Isothiocyanates, which are compounds found primarily in cruciferous vegetables, have been found to have chemopreventive activities against various cancers, including breast cancer. The most well studied isothiocyanates are sulforaphane, benzyl isothiocyanate, allyl isothiocyanate, and phenethyl isothiocyanate (PEITC). PEITC has been found to inhibit the growth of human breast cancer cells. Now a new study has reported that PEITC inhibits the growth of mammary tumors in a mouse model of HER2+ breast cancer.

Watercress, PEITC and breast cancer

Watercress is the richest source of PEITC, but it is also found in horseradish, turnips, mustard, garden cress, cabbage, cauliflower, brussels sprouts, rutabagas, and radishes. One study designed to examine the effects of dietary intake of watercress reported that significant levels of phenethyl isothiocyanate were found in the blood of the participants following a watercress meal.

Watercress has been shown to inhibit angiogenesis, the process by which tumors send out signals to induce surrounding normal tissues to grow new blood vessels into the tumor. Since tumors quickly outgrow their existing blood supply as they grow, angiogenesis is important to continued tumor growth and development.

Latest research finds PEITC inhibits HER2+ mouse tumor growth

The study referenced at the beginning of this news article was designed to examine the effects of PEITC in a mouse model of HER2/neu overexpressing (HER2+) breast cancer. To conduct the study, the authors used female mouse mammary tumor virus-neu mice. These mice spontaneously develop estrogen receptor negative (ER-) HER2+ mammary tumors. The mice were divided into two groups and fed either a standard diet or the same diet supplemented with 3 μmol PEITC/g for 29 weeks.

At this point, the number and size of mammary tumors in all the mice were assessed. Proliferation (as measured by Ki-67), apoptosis (programmed cell death), and angiogenesis were measured in tumor sections. In addition, various other analyses were performed, including determining the expression of proteins in mammary tumor sections.

The mice in the PEITC group were found to have a 53.13% lower incidence of macroscopic mammary tumors than the control group. The PEITC group also had a 56.25% reduction in microscopic mammary lesions greater than 2 mm. The inhibition of tumor growth was not found to be the result of suppression of HER2 expression. Instead, it was associated with lower proliferation and angiogenesis and greater apoptosis, as well as altered expression of several proteins. (This suggests that the chemopreventive effect of PEITC would hold for other types of breast cancer in addition to HER2+.) The authors conclude that PEITC inhibits the growth of mammary tumors in a mouse model with similarities to human breast cancer progression.

A note on PEITC supplements

It is inadvisable to take PEITC supplements. First, chemopreventive levels of PEITC can be obtained by including watercress and other cruciferous vegetables in the diet. Second, isothiocyanates may damage the DNA of normal cells at doses obtainable through use of concentrated sources (see Natural isothiocyanates: Genotoxic potential versus chemoprevention below).

Please see our article on breast cancer diet for HER2+ patients and survivors for more information.