Malignant ascites is a fluid, which builds up in the abdomen and contains cancer cells in the form of single cells or multicellular clusters called spheroids. Malignant ascites has been observed in patients suffering from ovarian, cervical, gastric, colorectal, pancreatic, endometrial or primary liver cancer. The spheroids are believed to play a major role in chemo resistance and metastasis of the cancer. To ease the discomfort of patients, malignant ascites (MA) is often drained from the abdomen using a procedure called paracentesis. MA retrieved via this minimal invasive procedure, is a great source for cancer spheroids, which can be used for testing chemotherapeutic drugs and drug combinations. We have optimised a workflow for concurrent monitoring of drug accumulation, drug response and drug metabolites in cancer spheroids. This new approach might be used to choose the best targeted therapy for each patient and thereby facilitate personalised medicine.