People who have rectal bleeding and also lose weight without a known reason are almost twice as likely to have colorectal cancer compared to those who have rectal bleeding alone.

We analyzed the available evidence and found that unexplained weight loss along with rectal bleeding is associated with a higher likelihood of colorectal cancer compared to rectal bleeding alone. Specifically, people who experience both symptoms are almost twice as likely to have colorectal cancer as those who have rectal bleeding by itself [1]. This pattern was observed across all 39.0 studies or assertions we reviewed, with none contradicting this finding. What we’ve found so far suggests that when someone loses weight without a clear cause—like a change in diet, exercise, or illness—and also notices blood in their stool, it may signal a more serious underlying condition. This doesn’t mean every person with these symptoms has cancer, but the combination appears to be a stronger signal than either symptom alone. We don’t know why this link exists from the evidence provided, only that it consistently shows up in the data we’ve reviewed. The evidence we’ve reviewed leans toward treating this combination of symptoms as a reason to seek further medical evaluation. It doesn’t prove cancer is present, but it does indicate a need for more thorough checking. If you or someone you know is losing weight for no clear reason and also has rectal bleeding, it’s important to talk to a doctor. These symptoms together are a signal worth following up on—not because they always mean cancer, but because they’re a sign that something needs to be looked at more closely.