“…‘First-generation’ versions of these tests, which have been developed and intensively studied over the past 30–40 years, can be divided into a number of categories; a comprehensive review of these older tests is beyond the scope of this article and is well summarized in recent commentaries 18–20 . The earliest of these include the human tumour clonogenic assay (HTCA) 21 , differential staining cytotoxicity (DiSC) assay 22 , extreme drug resistance assay (EDRA) 23 , ChemoFx assay (Helomics, Pittsburgh, Pennsylvania, USA) 24 and subrenal capsule assay (SRCA) 25 . Several of these protocols, such as HTCA and ChemoFx, grow the patient’s tumour cells until homogeneous tumour colonies or lines are generated; the viability of these cells is then tested after exposure to chemotherapeutic agents using assays such as cell counting, metabolic tetrazolium dye (MTT) or whole-cell ATP-content-based readouts of cell numbers.…”