Inclusion Criteria:  Adult patients (18 years and above) Patients with metastatic solid tumours that are candidates for systemic therapy (early lines are preferred). Numbers will be capped for frequent tumour types (breast cancer: 120 patients, NSCLC: 120 patients, colorectal cancer: 120 patients). There will be a cohort of 150 patients with rare tumours or tumours with rare histology (Eur. J. Cancer 2011; 47: 2493-2511). Patients will be recruited as they appear in clinical practice. Life expectancy of > 12 weeks. Patient showing an Eastern Cooperative Oncology Group (ECOG) Performance Status of ≤ 2. Patients eligible for reimbursed NGS (cfr. indications NGS convention) will also be tested by the local NGS panel although this is not required if the CGP is ISO 15189 accredited. In that situation, the CGP is considered the local NGS. Patients that are not eligible for reimbursed NGS testing may only be tested by CGP. Patients must have enough tissue from a metastatic (preferred) or primary lesion biopsy for local testing and CGP testing, sufficient to extract a minimum of 80 ng DNA diluted in TE 1x and 40-80 ng (80 ng recommended) RNA diluted in RNA-grade water for TSO500 library prep. The nucleic acid extract must meet the quality requirements specified in the protocol (See "TruSight Oncology 500 (TSO500) workflow - Workflow instructions for participant laboratories"). The tissue should not be more than 2 years-old and fixed in 10% neutral buffered formalin. Availability of metastatic biopsies retrieved after a previous therapy line are mandatory for patients treated with therapies that are known to induce acquired mechanisms of resistance (EGFR TKIs in NSCLC, aromatase inhibitors in breast cancer, TKIs in GIST…). Bone biopsies that undergo decalcification are not allowed. Patients can only be enrolled if they are also concomitantly registered in the Precision-1 study and the investigator agrees to subsequent registration of CGP-driven treatment given and the investigator assessed outcome on this and prior treatment (PFS based on RECIST 1.1 evaluation). Patients able to provide written informed consent prior to enrolment into a potential subsequent clinical trial.  Exclusion Criteria:  Life expectancy of less than 12 weeks. Inability to comply with protocol procedures. Known presence of severe hematopoietic, renal, and/or hepatic dysfunction (according to the local PI). No informed consent provided. Patient is not enrolled and followed as provided in Precision-1. Insufficient DNA/RNA quantity (<80 ng DNA, <40-80 ng RNA) and quality (dCq value >5 for DNA, DV200 value <20% for RNA), (See "TruSight Oncology 500 (TSO500) workflow - Workflow instructions for participant laboratories").