Method for predicting negative consequences of a treatment of a tumour patient with a therapy inducing p53 dependent apoptosis or a therapy interfering with the cell cycle characterised by the following steps: - determining the genetic status of the patient's tumour with respect to p53 by determining in a sample of body fluid or a tissue sample of the patient containing tumour cells or cell-free tumour DNA whether the whole p53 gene is present in native form or whether the p53 gene has one or more mutations; - predicting the tumour patient as - (i) a patient who will suffer negative consequences of a therapy interfering with the cell cycle if the whole p53 gene is present in native form; or - (ii) a patient who will suffer negative consequences of a therapy inducing p53 dependent apoptosis if the p53 gene has one or more mutations, wherein the therapy inducing p53 dependent apoptosis is - a treatment with methotrexate, 5-fluorouracil, capecitabine, gemcitabine or hydroxyurea; - a treatment with actinomycin D or anthracyclins, especially doxorubicin, daunorubicin, idarubicin, valrubicin, mitoxantrone or epirubicin; - a treatment with melphalan, oxazaphosphorins, especially cyclophosphamide, ifosfamide or busulfan; nitrosourea, especially carmustine, lomustine, semustine or procarbazine; or a treatment with cisplatin, carboplatin or oxaliplatin; - a treatment with thymidylate synthase inhibitors, especially raltitrexed or pemetrexed; - radiotherapy; - a treatment with estrogens, gestagens, anti-estrogens, especially tamoxifen, 3-hydroxy-tamoxifen, or chlortamoxifen; aromatase inhibitors, especially aminoglutethimide, formestan, anastrozol or letrozol; antiandrogens, especially cyproterone acetate or flutamide; gonadotropin-releasing hormone antagonists (buserelin, goserelin, leuprolerin, triptorelin); or - a treatment with antitumour antibodies, preferably a treatment with a HER2 inhibitor antibody, especially trastuzumab; with a thymidine kinase inhibitor antibody, especially gefitinib or erlotinib; with a EGFR inhibitor antibody, especially cetuximab, panitumumab or nimotuzumab; and wherein the therapy interfering with the cell cycle is - a treatment with camptothecins, especially irinotecan or topotecan; - a treatment with vinca alcaloids, especially vincristine, vinblastine, vindesine or vinorelbine;; or a treatment with taxanes, especially paclitaxel or docetaxel. - determining the genetic status of the patient's tumour with respect to p53 by determining in a sample of body fluid or a tissue sample of the patient containing tumour cells or cell-free tumour DNA whether the whole p53 gene is present in native form or whether the p53 gene has one or more mutations; - predicting the tumour patient as - (i) a patient who will suffer negative consequences of a therapy interfering with the cell cycle if the whole p53 gene is present in native form; or - (ii) a patient who will suffer negative consequences of a therapy inducing p53 dependent apoptosis if the p53 gene has one or more mutations, - a treatment with methotrexate, 5-fluorouracil, capecitabine, gemcitabine or hydroxyurea; - a treatment with actinomycin D or anthracyclins, especially doxorubicin, daunorubicin, idarubicin, valrubicin, mitoxantrone or epirubicin; - a treatment with melphalan, oxazaphosphorins, especially cyclophosphamide, ifosfamide or busulfan; nitrosourea, especially carmustine, lomustine, semustine or procarbazine; or a treatment with cisplatin, carboplatin or oxaliplatin; - a treatment with thymidylate synthase inhibitors, especially raltitrexed or pemetrexed; - radiotherapy; - a treatment with estrogens, gestagens, anti-estrogens, especially tamoxifen, 3-hydroxy-tamoxifen, or chlortamoxifen; aromatase inhibitors, especially aminoglutethimide, formestan, anastrozol or letrozol; antiandrogens, especially cyproterone acetate or flutamide; gonadotropin-releasing hormone antagonists (buserelin, goserelin, leuprolerin, triptorelin); or - a treatment with antitumour antibodies, preferably a treatment with a HER2 inhibitor antibody, especially trastuzumab; with a thymidine kinase inhibitor antibody, especially gefitinib or erlotinib; with a EGFR inhibitor antibody, especially cetuximab, panitumumab or nimotuzumab; - a treatment with camptothecins, especially irinotecan or topotecan; - a treatment with vinca alcaloids, especially vincristine, vinblastine, vindesine or vinorelbine;; or a treatment with taxanes, especially paclitaxel or docetaxel.