Method for analyzing the composition of circulating tumor cell population in a biological sample from an individual for use in the diagnosis or prognosis of a tumor comprising the steps a) isolation or enrichment of peripheral blood mononuclear cells (PMBCs) and CTCs from the biological sample, b) depleting hematopoietic cells from the isolated or enriched PMBCs and CTCs, c) testing the obtained cell suspension from step b) for at least two markers independently from each other selected from epithel markers, wherein the epithel markers are selected from the group comprising epithelial cell adhesion molecule (EpCAM), epithelial growth factor receptor (EGFR), cytokeratin, pan-cytokeratin (Pan-CK), E-Cadherin, and/or mesenchymal markers, wherein the mesenchymal markers are selected from the group comprising N-Cadherin and Vimentin, and/or tumor markers, wherein the tumor markers are selected from the group comprising AFP, KRT18, KRT19, TGFb, HIF1a, IGFBP1, IGFBP5, IGF, HGFAC, APC, VEGFA, PDGFA, FGFA, HIF1A, KDR1 (VEGFR), FGF2, HBsAg, ASGPR1, aSMA, Hep-Par-1, and/or markers for resistance namely C-Met, and/or stem cell markers namely CD133 and/or hematopoietic markers, wherein the hematopoietic marker is selected from the group comprising CD45 or CD15, and d) thereby identifying one or more subgroup(s) of CTCs in the CTC population of that biological sample, wherein the composition of subgroup(s) of CTCs is characteristic for a specific tumor, wherein the tumor is selected from the group of non-small cell lung cancer (NSCLC), metastatic renal cell carcinoma (mRCC). a) isolation or enrichment of peripheral blood mononuclear cells (PMBCs) and CTCs from the biological sample, b) depleting hematopoietic cells from the isolated or enriched PMBCs and CTCs, c) testing the obtained cell suspension from step b) for at least two markers independently from each other selected from epithel markers, wherein the epithel markers are selected from the group comprising epithelial cell adhesion molecule (EpCAM), epithelial growth factor receptor (EGFR), cytokeratin, pan-cytokeratin (Pan-CK), E-Cadherin, and/or mesenchymal markers, wherein the mesenchymal markers are selected from the group comprising N-Cadherin and Vimentin, and/or tumor markers, wherein the tumor markers are selected from the group comprising AFP, KRT18, KRT19, TGFb, HIF1a, IGFBP1, IGFBP5, IGF, HGFAC, APC, VEGFA, PDGFA, FGFA, HIF1A, KDR1 (VEGFR), FGF2, HBsAg, ASGPR1, aSMA, Hep-Par-1, and/or markers for resistance namely C-Met, and/or stem cell markers namely CD133 and/or hematopoietic markers, wherein the hematopoietic marker is selected from the group comprising CD45 or CD15, and epithel markers, wherein the epithel markers are selected from the group comprising epithelial cell adhesion molecule (EpCAM), epithelial growth factor receptor (EGFR), cytokeratin, pan-cytokeratin (Pan-CK), E-Cadherin, and/or mesenchymal markers, wherein the mesenchymal markers are selected from the group comprising N-Cadherin and Vimentin, and/or tumor markers, wherein the tumor markers are selected from the group comprising AFP, KRT18, KRT19, TGFb, HIF1a, IGFBP1, IGFBP5, IGF, HGFAC, APC, VEGFA, PDGFA, FGFA, HIF1A, KDR1 (VEGFR), FGF2, HBsAg, ASGPR1, aSMA, Hep-Par-1, and/or markers for resistance namely C-Met, and/or stem cell markers namely CD133 and/or hematopoietic markers, wherein the hematopoietic marker is selected from the group comprising CD45 or CD15, and d) thereby identifying one or more subgroup(s) of CTCs in the CTC population of that biological sample, wherein the composition of subgroup(s) of CTCs is characteristic for a specific tumor, wherein the tumor is selected from the group of non-small cell lung cancer (NSCLC), metastatic renal cell carcinoma (mRCC).