In standard Sage CRM some of columns are displayed internally through eWare dll, which are not removable.
For an example, you will find this on the Communication List, where we cannot remove the “Regarding” column.
If you are looking for this then yes it is possible to hide the columns from the list. You just need to do some customization at client side i.e. in the custom content of that particular list.
It is just not limited to “Regarding” field only, we can also handle other columns too.