A Study to Test Different Doses of BI 1701963 in Combination With Irinotecan in People With Advanced Bowel Cancer With Kirsten Rat Sarcoma Viral Oncogene Homologue (KRAS) Mutation

Inclusion Criteria: * Patient must have a confirmed activating KRAS mutation in CRC tumour tissue by local test. Activating mutations include but are not limited to: KRAS mutations in exon 2 (G12, G13), exon 3 (A59, Q61) and exon 4 (K117, A146) * Patients must have a histological or cytological diagnosis of CRC * Patients must have received at least first-line chemotherapy (oxaliplatin/ 5-Fluorouracil (5-FU)/ capecitabine et al treatment failure) for unresectable locally advanced or metastatic CRC * Must have at least one target lesion that can be accurately measured per RECIST version 1.1 * Must have Eastern Cooperative Oncology Group score of 0 or 1 * Must show adequate organ function defined as all of the following: 1. Absolute neutrophil count (ANC) ≥1.5 x 109/L; haemoglobin ≥9.0 g/dL; platelets ≥100 x 109/L without the use of hematopoietic growth factors within 4 weeks of start of Trial medication. 2. Total bilirubin ≤1.5 x Upper Limited of Normal (ULN), or ≤4 x ULN for patients who are known to have Gilbert's syndrome 3. Creatinine ≤1.5 x ULN. If creatinine is \>1.5 x ULN, patient is eligible if concurrent glomerular filtration rate (GFR) ≥30 mL/min (measured or calculated by CKD-EPI formula) 4. Aspartate Aminotransferase (AST) and Alanine Aminotransferase (ALT) ≤3 x ULN if no demonstrable liver metastases, or otherwise ≤5 x ULN * For patients participating in the combination dose escalation and expansion parts (Part B and C), must be eligible to receive treatment with irinotecan in accordance with the local label including Summary of Product Characteristics (SmPC), U.S. PI or Chinese Label * Must be at least 18 years of age at screening * Must have recovered from any previous therapy related toxicity to CTCAE grade ≤1 before the first dose (except for alopecia; stable sensory neuropathy must be CTCAE grade ≤2) * Signed and dated written informed consent in accordance with good clinical practice and local legislation prior to admission to the trial * further inclusion criteria apply Exclusion Criteria: * Previous anticancer chemotherapy, anticancer immunotherapy, and/or other anticancer biologic therapy within 3 weeks of the first administration of trial drug. Previous anticancer hormonal therapy within 2 weeks of first administration of trial drug * Previous treatment with a RAS, Mitogen-activated protein kinase (MAPK) or Son of Sevenless 1 (SOS1) targeting agent * For patients participating in the combination dose escalation and expansion parts (Part B and C only): Previous treatment with irinotecan * Radiotherapy within 4 weeks except as follows * Palliative radiotherapy to regions other than the chest is allowed up to 2 weeks prior to start of treatment * Single dose palliative radiotherapy for symptomatic metastasis within 2 weeks prior to start of treatment may be allowed but must be discussed with the sponsor * Major surgery (major according to the investigator's assessment) performed within 4 weeks prior to start of treatment or planned during the projected course of the trial, e.g. hip replacement * Previous treatment with any investigational agent(s) or targeted treatment within 28 days prior to start of treatment * Known history of hypersensitivity to any of the excipients of BI 1701963 tablets * History or presence of cardiovascular abnormalities such as uncontrolled Hypertension, congestive heart failure New York Heart Association (NYHA) classification of ≥3, unstable angina or poorly controlled arrhythmia which are considered as clinically relevant by the investigator; Myocardial infarction within 6 months prior to start of treatment * Left ventricular ejection fraction (LVEF) \<50% * Congenital long QT prolongation syndrome or mean resting corrected QT interval (QTcF) \>470 msec * further exclusion criteria apply