The research will be prospective, randomised, placebo controlled and double-blinded.The research will be carried on with regards to Helsinki Declaration and following the guidelines of Good Clinical Practice.

The investigators plan this research to be prospective, randomized, placebo-controlled and double blinded. It will be held according to Declaration of Helsinki and in harmony with Good Clinical Practice guidelines. All patients would be required to sign informed consent, approved by the Ethics Committee of Clinical Hospital Center (CHC) Rijeka.

All patients will have at their disposal current medications for diarrhea based on guidelines, and education regarding side effects and dietary recommendations will be undertaken. One cohort will also ingest a probiotic (OMNi-BiOTiC® 10AAD), while other cohort will take a placebo, same in colour, shape, taste and smell; both medications will be taken 2 per day, every 12 hours, over 84 days (6 chemotherapy cycles every 14 days). After 84 days, a regular examination will be undertaken. Total follow-up would be for two full cycles, at least 160 days. (Stool analyses will take place before and after chemotherapy(6-8 weeks after chemotherapy) and eventually three month later) Patients will be followed up in six main control points, t1, t2, t3, t4, t5, t6, which all represent the 1st day of matching 2-week-chemotherapy cycle. Each cycle starts exactly and at least 14 days from the first day of previous chemotherapy cycle. There would be no additional invasive procedures done for this study, regular blood examinations will be expanded with additional parameters. All patients would have the right to withdraw their written consent to participate in the study at any given time and for any reason whatsoever. (fecal analyses only before and 6-8 weeks after the last chemotherapy cycle)

Inclusion Criteria:

• A histologically confirmed diagnosis of colorectal cancer with metastasis;
• Patients older than 18 years of age;
• Patients starting first line of chemotherapy (FOLFIRI protocol);
• Signed patient consent form.

Exclusion Criteria:

• Present ileostomy;
• Decompensated patients;
• Terminal stage patients (<6 months life expectancy);
• Patients not mentally able to adhere to the protocol;
• Patients using >3 yoghurts per week or any other probiotics;
• Or any other condition which would not allow safe administration of the drugs.