Foreach listbox item c#

I'm pretty sure this has worked before in some code I have written, not sure what I am missing here.

The following code does not change the string values in my list. Why?

var items = listBox1.Items.Cast[].ToList[]; items.ForEach[item => item = [!chkBox1.Checked] ? "move " + item : "move -check " + item];

EDIT : Just to clarify, the list remains the same as when it was created.

EDIT : Apologies, the items list [listBox1.Items] contains alphanumeric strings as follows.

J00123456

J00123344

J00123458

Also, just to confirm, I have successfully done this with a custom list of T [shown below], which is why I thought it would work here.

var tapes = new List[]; ... //Populated list tapes.ForEach[x => x.vItem = "tapelib 3592 -eject " + x.vItem]; //Works here