touch on vs concern

touch on is not a noun while concern is a noun.

Word	Noun	Adjective	Verb	Adverb
touch on	No	No	Yes	No
concern	Yes	No	Yes	No

As verbs, touch on and concern are synonyms defined as:

Other synonyms of touch on include bear on, come to, have to do with, pertain, refer, relate, touch.

touch on (noun)	concern (noun)
	something that interests you because it is important or affects you
	something or someone that causes anxiety; a source of unhappiness
	a feeling of sympathy for someone or something
	an anxious feeling
	a commercial or industrial enterprise and the people who constitute it

touch on (verb)	concern (verb)
restore by replacing a part or putting together what is torn or broken	be relevant to
have an effect upon	be on the mind of
refer to or discuss briefly
be relevant to