Determination of Microbiological Factors Associated With Poor Response to Neoadjuvant Treatment in Rectal Cancers

This study is investigating whether the bacteria living in your gut (your microbiome) might affect how well rectal cancer responds to treatment before surgery (called neoadjuvant therapy). Researchers will collect stool samples to study these bacteria. **You may be eligible if...** - You have been diagnosed with rectal cancer (specifically in the lower or middle rectum, stages II or III) - You are scheduled to receive treatment such as radiation and/or chemotherapy before surgery - You are 18 years old or older **You may NOT be eligible if...** - You have taken antibiotics in the month before the stool sample is collected - You already have a colostomy bag (ostomy) - You have previously been treated for rectal cancer - You are pregnant or breastfeeding - You have had other cancers in the past 5 years (with some exceptions) Talk to your doctor to see if this trial is right for you.