Patient description: The patient is a 42 year-old postmenopausal woman who had a screening sonogram which revealed an abnormality in the right breast. She had no palpable masses on breast exam. Core biopsy was done and revealed a 1.8 cm infiltrating ductal breast carcinoma in the left upper outer quadrant. Lumpectomy was done and the surgical margins were clear. The tumor was HER2-positive and ER/PR negative. Axillary sampling revealed 1 positive lymph node out of 12 sampled. CXR was unremarkable. She is using “well women” multivitamins daily and no other medication. She smokes frequently and consumes alcohol occasionally. She is in a relation with only one partner and has a history of 3 pregnancies and live births. She breastfed all three children.

Clinical trial eligibility criteria: eligible ages (years): 18.0-999.0,  Right-sided Colon Cancer Right-sided Colon Adenoma for track 1 and 2a Male and female patients above 18 years of age with either: right-sided colon cancer tumor with adenocarcinoma histologically verified scheduled for open or laparoscopic resection at the Department of Surgery, Herlev Hospital or Zealand University Hospital for track 1. Right-sided adenomas ≥2cm in diameter endoscopically verified scheduled for endoscopic mucosal resection at the Department of Surgery, Herlev Hospital or Zealand University Hospital for track 2a ASA I,II or III The caecum must be reached by the endoscope. for retrospective controls (track 2b): Male and female patients above 18 years of age who were operated for colon adenoma ≥2cm in diameter in the right hemicolon in 2018 at Department of Surgery, Zealand University Hospital. They will be matched 2:1 with the patients included in track 2a (cases) based on age and gender and pathology of the tumor  for track 1 and track 2a 1. Patients with previous allergic reaction to fosfomycin and/or metronidazole 2. Patients under current antibiotic treatment or patient who had the last dose of antibiotics 30 days prior to inclusion. 3. Patients with a non-passable tumor or patients where a part of the tumor is not visible during endoscopy (Track 1) 4. Patients with neoadjuvant chemotherapy or radiation 12 months prior to the resection. 5. Patients with a history of familial adenomatous polyposis (FAP) or hereditary nonpolyposis colorectal cancer (HNPCC) 6. Patients with a history of inflammatory bowel disease (IBD) 7. Patients under current treatment with warfarin (Marevan) and phenprocoumon (Marcoumar), or NOAK such as dabigatran (Pradaxa®), rivaroxiban (Xarelto®), edoxaban (Lixiana®) or apixaban (Eliquis®) 8. Patients under current treatment with Fenemal (Phenobarbital) 9. Patients who previously have received a fecal transplantation 10. Patients who have previously had colorectal cancer, and are now presenting with a secondary colon tumor. 11. Patients with a current alcohol use disorder (AUD): defined as a patient who are currently drinking 8 or more drinks/week for women and 15 or more drinks/week for men. 12. Predictable poor compliance (psychiatric disease, not speaking fluent Danish, mentally, impaired etc) 13. Patients with an American Society of Anaesthesiologists physical status 14. Classification (ASAscore) of IV. 15. Patients unable to be sedated 16. Pregnancy or lactation (fertile women must have a negative serum or urine pregnancy test to participate) 17. Fertile women who do not use safe contraception during the study period 18. Following contraceptive methods are acceptable when used consistently and in accordance, with both the product label and the instructions of the physician are Oral contraceptive, either combined or progestogen alone Injectable progestogen Implants of levonorgestrel Estrogenic vaginal ring Percutaneous contraceptive patches Intrauterine device or intrauterine system with a documented failure rate < 1% per year Male partner sterilization (vasectomy with documented azoospermia) prior to female patient ́s entry into the study, and this male is the sole partner for that patient Double barrier method: condom with spermicidal agent (foam/gel/film/cream/suppository), condom and occlusive cap (diaphragm or cervical/vault cap) with vaginal spermicidal agent (foam/gel/film/cream/suppository) for retrospective controls (track 2b)