focus on vs concern

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

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

As verbs, concern is a hypernym of focus on; that is, concern is a word with a broader meaning than focus on:

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

focus 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

focus on (verb)	concern (verb)
center upon	be relevant to
	be on the mind of