Handling overlapping asynchronous POST requests

We have implemented How to Use POST for Asynchronous Tasks in our project for long running tasks.

My question is how we can handle the case wherein we have multiple POST requests issued back-to-back from the same client. In this case, only the last POST request is what the client really is interested in. When a POST triggers a background thread, a subsequent POST also tries to trigger another background thread.

This effectively means that apart from the last POST request, the others result in wasteful computation

Are there any design patterns to address this?