A composition comprising a non-fiber organic extract of psyllium which is anti-tumorigenic is described. The composition both restores gap junctional intercellular communication (GJIC) and inhibits anchorage independent growth of mammalian cells which have been transformed with the ras oncogene. The composition is a useful chemotherapy and chemopreventative agent. The composition was identified using a novel method for determining the anti-tumorigenic potential of a compound or composition.