Yes, TOPHUS is a Scrabble word!

Letter values in Scrabble US: T 1, O 1, P 3, H 4, U 1, S 1.

Is it a valid word?

TOPHUS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a deposit of urates around a joint or in the external ear; diagnostic of advanced or chronic gout
an incrustation that forms on the teeth and gums

Not playable in Scrabble US: CHALKSTONE.