**Abstract**

The number of patients diagnosed with prostate and bladder cancer is increasing worldwide and one of the most important challenges remains the development of effective, safe and economically viable antitumor drugs. Clinical approval for drugs tested in preclinical studies enabling them to enter phase I clinical trials is essential. Cell lines are *in vitro* model systems that are widely used in different fields of medical research, especially basic cancer research and drug discovery. Their usefulness is primarily linked to their ability to provide an indefinite source of biological material for experimental purposes. Under the right conditions and with appropriate controls, authenticated cancer cell lines retain most of the genetic properties of the cancer of origin. Studies conducted during the initial development of drugs such as toxicity, corrosion and drug activity were carried out on animals; however, in the past two decades, alternatives have been sought due to the fact that animals do not effectively model to human *in vivo* conditions and unexpected responses are observed in the studies. Also, more than 100 million animals were used and billion dollars were spent for animal toxicity experiments. Cell culture studies made positive contributions to the initial development of drugs and is highly desirable, as it provides systems for ready, direct access and evaluation of tissues. Contrary to animal studies, less cost and the need for low drug and a short response time are the characteristics for *in vitro* cell culture methods. *In vitro* tumor models are a necessary tool, in not only the search for new substances showing antitumor activity but additionally for assessing their effectiveness. This chapter reviews the main features of primary cancer cell cultures, provides an overview of the different methods for their selection and management, and summarizes the wide range of studies that can be performed with them to improve the understanding of prostate and bladder cancer preclinical treatment processes.

**Keywords:** Primary cell culture, preclinical studies, prostate and bladder cancer, *in vitro* model
