Colorectal cancer (CRC) is the second leading cause of cancer-related death in the United States and Europe. Although selected patients with oligometastatic CRC undergo systemic therapy and surgery/local ablative therapy in curative intent, the treatment approach for the majority of metastatic CRC (mCRC) patients remains palliative with a median overall survival (OS) ranging between 9-38 months depending on various prognostic and predictive factors. Particularly in advanced stages (in the third line of therapy and beyond), interesting and promising results have recently been achieved with various treatment approaches. The aim of this registry is to establish a disease-specific registry to evaluate the treatment landscape of patients with mCRC who have already received at least two lines of therapy.

This registry aims at retrospectively and prospectively evaluating the treatment landscape and clinical outcome of mCRC ≥3L in a collective attempt by including multiple oncologic centers in Austria.

Patient medical, testing and treatment information will be obtained through extraction of data from existing patient medical charts. Longitudinal follow-up data, including survival and tumor progression, will also be extracted from patient medical charts. Imaging studies ≥3L will be centrally collected in a virtual "imaging-bank" and tumor tissue samples of deceased patients will be stored in a central "bio-bank". Additionally, further biomaterial (e.g. ctDNA samples or DNA from DPYD genotyping) may be requested from the centres in case of specific research questions. The patient follow-up data will be obtained until patient death or loss to follow-up.

For documentation in the registry, no further diagnostic or therapeutic measures are required than those already necessary in general. Participation in the registry must not interfere with treatment routines. Only routine data, which have already been recorded in the patients' medical charts, is transferred to the electronic Case Report Forms. To maintain patient confidentiality, each patient will be assigned a unique patient identifying number upon enrollment; this number will accompany the patients' medical and other registry information throughout the lifetime of the registry.

A written consent must be obtained prior to the input of data. No informed consent is required from deceased patients.

Data will be collected from all sites willing to participate.

Inclusion Criteria:

• patients ≥ 18 years with tissue-based diagnosis of mCRC
• ≥ 2 prior lines of palliative systemic therapy including 5-FU, irinotecan, oxaliplatin, anti-VEGF, anti-EGFR (in case of RAS/BRAF wildtype), anti-PD1- therapy (in case of MSI/MMRd) . (Exception: Patients who have received mFOLFOXIRI +/- anti-VEGF or anti- EGFR- 1L therapy or patients with ineligibility to receive 5-FU, oxaliplatin or irinotecan can be included after 1st line.)

Exclusion Criteria:

• Due to the non-interventional design of this registry, there are no specific exclusion criteria

Interested sites that treat patients in this indication will be invited to participate in this registry