The hazelnut and chocolate spread was being pulled from shelves after the study.
It said palm oil was more likely to contain carcinogenic agents compared to other vegetable oils.
Ferrero say switching ingredients would result in an inferior spread which wouldn't be as smooth.
The report for the European Food Safety Authority (EFSA) came out last May.
It said palm oil contains particularly high levels of contaminants, when heated about 200 degrees Celcius.