Trial Utilizing Metronidazole to Optimize the Microbiome of Rectal Adenocarcinoma Undergoing Neoadjuvant Therapy

This study tests whether adding an antibiotic called metronidazole to standard treatment for locally advanced rectal cancer changes the gut microbiome (the community of bacteria in the bowel) in a way that could improve how the cancer responds to treatment. Researchers believe certain gut bacteria may affect how well chemotherapy and radiation work. **You may be eligible if:** - You are 18 or older with locally advanced rectal cancer (T3, T4, or spread to lymph nodes) - You are being treated with total neoadjuvant therapy (chemotherapy and radiation before surgery) - You have not received chemotherapy for this cancer before - You are in good general health (ECOG score 2 or lower) - Your blood counts and organ function are within acceptable ranges **You may NOT be eligible if:** - You have already received chemotherapy for this cancer - You are under 18 years old - You have uncontrolled hepatitis B or other significant health conditions - Your organ function does not meet minimum requirements Talk to your doctor to see if this trial is right for you.