**4.2.3 Epithelial immunoSPOT (EPISPOT)**

A technique that allows the detection of only viable cells after a CD45+ cell depletion was introduced for CTC analysis from bone marrow aspirates and blood samples (Alix-Panabieres et al., 2008; Alix-Panabieres et al., 2007; Braun et al., 2005). This technique was designated EPISPOT (epithelial ImmunoSPOT). It is a protein-secreting profiling based on the secretion or active release of specific marker proteins using an adaptation of the enzymelinked immunospot technology. As immunospots are the protein fingerprint left only by the viable releasing epithelial cells, a cell culture is needed to accumulate a sufficient amount of the released marker proteins (Table 2). The dying cells do not secrete adequate amounts of protein and are not detected (Alix-Panabieres et al., 2005; Alix-Panabieres et al., 2008; Alix-Panabieres et al., 2007; Czerkinsky et al., 1983). This assay can also provide important information on the profile of secreted proteins potentially relevant for metastasis formation. However, this technique has still to be validated in large-scale clinical studies on cancer patients (Alix-Panabieres et al., 2008; Alix-Panabieres et al., 2007). After the enrichment and isolation of the CTC, the next step is to identify, characterize and finally enumerate them. The CTC can be identified by indirect or direct methods. But these important steps need tumor markers specific to the CTC seeked.
