The performance of a biomass adapted to Oncological Ward Wastewater (OWW) in a membrane bioreactor (MBR) was compared with that of a municipal WWTP, on the removal of pharmaceutical molecules and more specifically on their overall resistance and purifying ability in the presence of pharmaceutical cocktails. Sorption and biotransformation mechanisms on two antineoplastics, one antibiotic and a painkiller were evaluated. Sludge acclimated to OWW allowed for a 34% increase in the removal rate and in the minimum inhibition concentration. The percentage of the amounts of specific pharmaceutical compounds removed by biotransformation or by sorption were measured. These results are positive, as they show that the observed removal of pharmaceutical molecules by biomass acclimated to OWW can mostly be attributed to developed biotransformation, unlike the biomass from the municipal WWTP for which sorption is sometimes the only removal mechanism. The biotransformation kinetic and the solid-water distribution coefficients in this study show good agreement with literature data, even for much higher pharmaceutical concentrations in OWW.