From Lexicanum

Enhanced Warriors are standard Chaos Space Marines who have taken part in the experiments performed by Fabius Bile and have been 'improved' in some way through the use of genetic engineering and drugs, although it is just as likely that they will devolve into raving beasts. Sometimes they are subject to genetic corruption and turn into monsters, although when successful his mutations are stable and the warriors gain in speed and strength.¹

Sources

• ¹:Codex: Chaos Space Marines (3rd Edition, 2nd Codex)