At least one embodiment of the invention relates to bone marrow precursor cells or bone marrow cells of a patient, the cells labeled with at least one contrast agent suitable for an imaging method, for use in an imaging method for diagnosing a metastasizing cancer, wherein the local accumulation of the labeled precursor cells or bone marrow cells indicates the presence of a metastasizing tumor growth. At least one embodiment also relates to a method for imaging a metastasizing tumor tissue in a patient, wherein a) bone marrow precursor cells or bone marrow cells are extracted from a patient, b) these precursor cells or bone marrow cells are labeled with at least one contrast agent suitable for an imaging method, c) the precursor cells or bone marrow cells thus labeled are retransplanted or reinjected into the patient, and d) the presence of metastasizing tumor cells is depicted with an imaging method. At least one embodiment also relates a method for imaging a metastasizing tumor tissue, wherein a suitable imaging method is used to image bone marrow precursor cells and/or bone marrow cells that are accumulated in a metastasizing tumor tissue and labeled with at least one contrast agent suitable for an imaging method.