The goal of this phase III, open-label, non-inferiority randomized controlled clinical trial is compare upfront dose-reduced chemotherapy with the standard dose chemotherapy in older patients ( ≥70 years) with metastasized colorectal cancer, with regard to progression-free survival (PFS). The choice between monotherapy (a fluoropyrimidine) and doublet chemotherapy (a fluoropyrimidine with oxaliplatin) will be made for each individual patient based on expected risk of chemotherapy toxicity (according to the G8 screening). Patients classified as low risk of toxicity will be randomized between doublet chemotherapy in either full-dose, or with an upfront dose-reduction of 25%. Patients classified as high risk will be randomized between monotherapy in either full-dose or upfront dose-reduction.

Primary outcome is PFS. Secondary endpoints include grade ≥3 toxicity, QoL, physical functioning, overall survival, number of treatment cycles, dose reductions, hospital admissions, cumulative received dosage and cost-effectiveness.

Treating older adults with chemotherapy remains a challenge, as they are strongly underrepresented in clinical trials and no robust guidelines for treating older patients exist. Moreover, older adults are at increased risk of chemotherapy-related toxicity, resulting in decreased quality of life (QoL), increased hospital admissions and high health care costs. Therefore, the aim of the DOSAGE study is to demonstrate that upfront dose-reduced chemotherapy in patients with metastasized colorectal cancer is non-inferior to full-dose treatment with regard to progression-free survival (PFS). Treatment plans (monotherapy or doublet chemotherapy) will be based on expected risk of treatment toxicity for the individual patient (according to the Geriatric 8 (G8) questionnaire). The investigators expect that this treatment strategy will lead to less grade ≥3 toxicity, less early treatment continuation and hospitalizations and a better QoL and physical functioning.

The DOSAGE study is a phase III, open-label, non-inferiority, randomized controlled clinical trial in patients aged ≥70 years with metastasized colorectal cancer eligible for palliative chemotherapy. All participating patients will undergo geriatric screening by the G8 questionnaire and will be classified as "low risk of toxicity" (G8-score of 15 or higher) or "high risk of toxicity" (G8-score of 14 or lower or judged as "high toxicity risk" by their treating oncologist). Patients classified as low risk will be randomized between a fluoropyrimidine and oxaliplatin in either full-dose, or with an upfront dose-reduction of 25%. Patients classified as high risk will be randomized between fluoropyrimidine monotherapy in either full-dose or upfront dose-reduction. Addition of targeted treatment (bevacizumab or epidermal growth factor receptor (EGFR) inhibition) is allowed. Patients with a moderate renal impairment (GFR 30- 50 mL/min) will be treated with 25% reduced starting dose of capecitabine when randomized for full dose treatment and treated with 40% reduced starting dose when randomized for upfront dose reduction.

Primary outcome is PFS. Secondary endpoints include grade ≥3 toxicity, QoL, physical functioning, overall survival, number of treatment cycles, dose reductions, hospital admissions, cumulative received dosage and cost-effectiveness. Given a non-inferiority margin of 8 weeks, 587 patients will be included (293/292 patients per arm).

Inclusion Criteria:

• Patients aged 70 years or older with colorectal cancer and distant metastases without localized treatment options.
• Patients who are candidates for first-line palliative chemotherapy as judged by their treating oncologist
• Being able to understand the Dutch language
• Adequate bone marrow and organ function: Absolute neutrophil count (ANC) > 1.5 x 10^9 mmol/L, Hemoglobin (Hb) > 6.0 mmol/L, Platelets >100 x 109 / L, Serum bilirubin ≤ 2 x upper limit of normal (ULN), serum transaminases ≤ 3 x ULN without presence of liver metastases or ≤ 5x ULN with presence of liver metastases.

Exclusion Criteria:

• Patients who received prior palliative chemotherapy
• Patients in whom local treatment of metastases is scheduled (i.e. liver surgery or stereotactic radiotherapy)
• Candidates for triple chemotherapy
• Patients who received prior adjuvant chemotherapy in the one year before inclusion in the study (chemotherapy before that time is allowed)
• Patients with complete or incomplete dihydropyrimidine dehydrogenase (DPD) deficiency
• Patients with Microsatellite instable (MSI)-high colorectal cancer
• Patients with HIV or active hepatitis
• Patients with severe kidney failure (defined as GFR ≤30ml/min)
• Patients with severe cognitive deficits making informed consent not possible

Which parts of your data(sets) will you select for publication?

The datasets generated during and/or analysed during the study will not be publicly available due to participant privacy but will be available from the corresponding author on reasonable request

Are there any restrictions placed on sharing/reuse of some/all of your data due to one or more of the following options? Signed informed consent Research agreement

Will you publish your data open access or with restricted access? Restricted access

Publishing your data (partly) with 'restricted access': what is the reason for this? Data contains privacy-sensitive information Contractual obligations Reuse by third-party through DSA.

Where will you publish your (meta)data? I will not publish (meta)data outside the LUMC

The datasets generated and/or analysed during the current study are not publicly available due to patient privacy but are available from the corresponding author on reasonable request