Abstract: The present invention relates to a method for isolating cancer cells from body fluids containing cells. The invention also relates to sets for carrying out said method, cancer cells isolated from body fluids, cell lines established therefrom or derived cell constituents, the use thereof as therapeutic agents or targets, and pharmaceutical or veterinary products containing them. The inventive method is based on the idea that body fluids containing cells are comprised of different sized and different shaped cells and groups of cells. According to the invention, body fluids containing cells or fractions of said body fluids are filtered in a sieve that retains cancer cells. The isolation and characterization of cancer cells is highly important, especially in the field of oncology, in order to respond to questions related to diagnostics, prognoses, therapeutics and scientific matters in human medicine and veterinary medicine.