Over the past ten years, a number of scientific studies (see here and here and here for the original peer-reviewed papers) have suggested that suggests that that black raspberries have anti-cancer properties.
Although the exact mechanism of this cancer inhibition have not been fully determined, it seems most likely that this is due to some of the phytonutrients black raspberries, perhaps the polyphenolic compounds, are responsible.
Further research in the near future on this topic is likely; however, you do not need to wait to find out the biochemical details to benefit today.
I suggest you add black raspberries to your diet. If you cannot find black raspberries, it appears that blackberries have very similar anti-cancer properties as well.