Rectal polyps take about 8 to 10 years before they turn malignant. You will have developed a lot of symptoms till then, like weight loss, chronic diarrhea or constipation, blood loss via stool, and anemia. It is advisable to get treated right at the onset of the symptoms. Also, keep in mind that rectal polyps tend to recur. If you have had a polyp removed, visit your doctor regularly and get screening tests done.