Yes, SARCOMA is a Scrabble word!

Letter values in Scrabble US: S 1, A 1, R 1, C 3, O 1, M 3, A 1.

Is it a valid word?

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

a usually malignant tumor arising from connective tissue (bone or muscle etc.); one of the four major types of cancer