Dialog Box - Combo_Box - Entities relating to each other

I have a dialog box as shown in the screenshot with 2 combo-box entities (And a text entry entity but that is not relevant to the question)
As things stand the content for each Combo_Box can be populated independently of each other.
I want the secondary Combo_Box to have it's Content populated as a function of the first Combo_Box.
Is this possible?

1000000 thankyous!

You'll need to use a Detached Dialog so that you can run a message loop and respond to events. You can then respond to the event that fires when the first drop-down's selection changes, and clear out and re-populate the second drop-down accordingly.

Thank you Leo!