Inclusion Criteria:

          -  Written informed consent according to ICH/GCP regulations before inclusion and prior
             to any trial-related investigations.

          -  Histologically confirmed diagnosis of adenocarcinoma of the colon.

          -  Stage II (pT3/T4 N0 cM0) or stage III (pTx pN+ cM0) colon cancer.

          -  Availability of cancer tissue for central molecular testing.

          -  Presence of predefined, activating PIK3CA mutation in exons 9 or 20 (centrally
             assessed).

          -  Complete resection of the primary tumor (R0) within 14 weeks maximum before
             registration.

          -  WHO performance status 0-2.

          -  Age between 18-80 years.

          -  Adequate hematological values: hemoglobin ≥ 80 g/L, platelets ≥ 50 x 109/L.

          -  Adequate hepatic function: total bilirubin ≤1.5xULN, AST ≤2.5xULN, ALT ≤2.5xULN, AP
             ≤2.5xULN.

          -  Calculated creatinine clearance > 30 mL/min, according to the formula of
             Cockcroft-Gault.

          -  Women with child-bearing potential are using effective contraception, are not pregnant
             or lactating and agree not to become pregnant during trial treatment. A negative
             pregnancy test before inclusion (within 7 days) into the trial is required for all
             women with child-bearing potential.

        Exclusion Criteria:

          -  Previous or concomitant malignancy within 3 years of registration, except for
             adequately treated cervical carcinoma in situ or localized non-melanoma skin cancer.

          -  Multiple adenocarcinomas of the colon.

          -  Rectal cancer (defined as distance from anal verge to proximal/oral tumor edge ≤15
             cm).

          -  Severe or uncontrolled cardiovascular disease (congestive heart failure NYHA III or
             IV, unstable angina pectoris, history of myocardial infarction) within three months
             prior to registration.

          -  Systemic rheumatic diseases or degenerative disorders affecting the musculoskeletal
             system with a relevant risk of requiring treatment with NSAIDs in the future.

          -  Comorbidities that require regular (i.e. more than 3x per month, any dose) intake of
             acetylsalicylic acid or other NSAIDs or COX-2 inhibitors.

          -  Clinically relevant upper gastro-intestinal bleeding within 12 months prior to
             registration.

          -  Presence of any bleeding disorder that is an absolute contraindication to the use of
             aspirin.

          -  General tendency to hypersensitivity and history of asthma triggered by salicylates or
             substances with a similar mechanism of action, and non-steroidal anti-inflammatory
             drugs in particular

          -  Any serious underlying medical condition, at the judgment of the investigator, which
             could impair the ability of the patient to participate in the trial (e.g. uncontrolled
             infection, active autoimmune disease, uncontrolled diabetes).

          -  Concurrent treatment with other experimental drugs or treatment in an interventional
             clinical trial within 30 days prior to trial entry. Concomitant use of adjuvant
             chemotherapy for stage III and high risk stage II colon cancer according to
             international treatment guidelines is allowed (chemotherapy regimens include
             intravenous 5-fluorouracil or oral capecitabine either alone or in combination with
             intravenous oxaliplatin).

          -  Psychiatric disorder precluding understanding of trial information, giving informed
             consent or interfering with compliance for oral drug intake.

          -  Any familial, sociological or geographical condition potentially hampering proper
             staging and compliance with the trial protocol.

          -  Known or suspected hypersensitivity to any component of the trial drug or any agent
             given in association with this trial.

          -  Known galactose-1-phosphate uridyl transferase deficiency, UDP galactose 4 epimerase
             deficiency, galactokinase deficiency, orFanconi-Bickel syndrome, congenital lactase
             deficiency,or glucose-galactose malabsorption (due to the lactose-containing placebo).

          -  Any concomitant drugs contraindicated for use with the trial drug according to the
             approved product information.