Neuroendocrine prostate cancer (NEPC) is a lethal subtype of prostate cancer (PCa). Research of NEPC has been hampered by a lack of clinically relevant in vitro cell models. NCI-H660 cell is the unique bona fide NEPC cell line derived from a patient, available for in vitro study of NEPC disease. However, this cell grows slowly as floating attached clusters, making regular in vitro cell assays such as proliferation assay and colony formation assay challenging. This protocol provides a simple and practical solution to this technical hurdle.