How to display all parent and child custom taxonomies (get_the_term_list)

I am wondering how to to display ALL the parent and child custom taxonomies with the function get_the_term_list… Let me explain:

I’m running a popular paid plugin and they are using custom taxonomies to make custom categories. I have a parent custom categories with a child and sub-child custom categories (essentially identical to a normal set of hierarchical categories) like so…

XYZ
– abc
– 123
I have this piece of code: <?php if ( $post->post_type == 'post' ) the_category(', '); else echo get_the_term_list( $post->ID, APP_TAX_CAT, '', ', ', '' ); ?> but it only displays the last category ‘123’.

I would like the piece of code to show the ‘XYZ and the ‘abc’ categories inline as well.

Thanks heaps,
Pete