Yes, XANTHOMAS is a Scrabble word!

Letter values in Scrabble US: X 8, A 1, N 1, T 1, H 4, O 1, M 3, A 1, S 1.

Is it a valid word?

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

a skin problem marked by the development (on the eyelids and neck and back) of irregular yellow nodules; sometimes attributable to disturbances of cholesterol metabolism