Wasabi (Wasabi japonica) is a member of the Brassica, or cruciferous, family of vegetables. It grows naturally along stream beds in mountain river valleys in Japan.
The Wasabi paste that is often served in Japanese sushi restaurants is typically not pure Wasabi japonica. Most of these restaurants substitute wasabi with less expensive European horseradish. Even though it contains shorter-chain isothiocyanates, European horseradish does not contain the longer-chain isothiocyanates which has been found beneficial to health and is found in Wasabi japonica.
Wasabi japonica contains the following phytochemicals: 
- 6-(methylsulfinyl)hexyl isothiocyanate (6-MITC or 6-HITC)
- Monogalactosyl diacylglycerides
The naturally occurring compound 6-(methylsulfinyl)hexyl isothiocyanate (6-MITC) has been reported as having specific medicinal activities:
- Anti-inflammatory 
- Chemopreventive 
- Antimelanoma 
A study published in Phytochemistry in March 2006 found that 6-methylsulfinylhexyl isothiocyanate (6-HITC) was able to inhibit cell proliferation in human monoblastic leukemia U937 cells. The abstract of the study concluded that 6-HITC is potentially useful as a natural anti-cancer agent:
“The ethanol extract from Japanese horseradish wasabi was found to inhibit cell proliferation in human monoblastic leukemia U937 cells by inducing apoptotic cell death. Separation by methods including silica gel chromatography and preparative HPLC gave an active compound, which was identified as 6-methylsulfinylhexyl isothiocyanate (6-HITC). Several lines of evidence indicated that 6-HITC induced apoptosis in U937 cells and human stomach cancer MKN45 cells. Thus, 6-HITC is potentially useful as a natural anti-cancer agent.” 
Scientists at Japan’s Kanazawa Gakuin College learned that 6-MITC has similar properties against breast cancer and melanoma cells. The authors concluded that because of the low dosages required, 6-MITC has the potential to control cancer cells of all types. 
Hasegawa K, Miwa S, Tsutsumiuchi K, Miwa J. Allyl isothiocyanate that induces GST and UGT expression confers oxidative stress resistance on C. elegans, as demonstrated by nematode biosensor. PLoS ONE 2010;5 (2) : e9267
 T. Uto, D. X. Hou, O. Morinaga, and Y. Shoyama, “Molecular mechanisms underlying anti- inflammatory actions of 6-(methylsulfinyl)hexyl isothiocyanate derived from wasabi (Wasabia japonica),” Advances in Pharmacological Sciences, vol. 2012, Article ID 614046, 8 pages, 2012. View at Publisher · View at Google Scholar
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 Y. Fuke, S. Shinoda, I. Nagata et al., “Preventive effect of oral administration of 6-(methylsulfinyl)hexyl isothiocyanate derived from wasabi (Wasabia japonica Matsum) against pulmonary metastasis of B16-BL6 mouse melanoma cells,” Cancer Detection and Prevention, vol. 30, no. 2, pp. 174–179, 2006. View at Publisher · View at Google Scholar · View at Scopus
 Nomura T, Shinoda S, Yamori T, et al. Selective sensitivity to wasabi-derived 6-(methylsulfiny)hexyl isothiocyanate of human breast cancer and melanoma cell lines studies in vitro. Cancer Detect Prev. 2005;29(2):155-60.