Reject Pull Request creation request if PR message body validation fails

Is there a way we can reject the Pull Request creation if certain conditions fail ?

I am developing a GitHub App in  nodejs  and  probot  and would like to reject the pull request creation when the developer clicks on the  “Create pull request”  button if the validation (like checking for the presence of some pattern in the body of pull request) fails for Pull Request body.

So, fundamentally the Pull Request should not be created in the first place(and user should be taken back to the PR creation page), if certain validation fails.

i.e. be on the same pull request creation page, if validation of pull request body(or just any other logic) fails.