Both animal data and human data are showing protective effects of various berries, including prevention of cancer.  Although multiple berries are high in anti-oxidant value, today's spotlight is on black raspberries as a cancer preventative agent.

Previously, researchers at Ohio State found that a concentrated freeze dried mix preparation of black raspberries favorably affected some 460 genes to reduce chemical carcinogenesis in a rat model.  In that study, esophageal cancer was the target.  Subsequently the same group and others have shown that the same preparation helps decrease the risk that a precancerous condition (Barrett's Esophagus) will go on to cancerous transformation.  It also reduced reflux episodes and had a protective effect on the lining of the esophagus from direct oxidative stress. 

Is this just a direct effect from contact with black raspberries or is there some systemic component to it as well which might reduce the risk of developing other cancers? That is unclear, and more research is needed. However,  since many of us suffer from acid reflux, this is not a bad strategy which appears to improve quality of life and preliminary research shows a plausible cancer preventative effect as well.