antitumor vs antineoplastic

antitumor is not a noun while antineoplastic is a noun.

Word	Noun	Adjective	Verb	Adverb
antitumor	No	Yes	No	No
antineoplastic	Yes	Yes	No	No

As adjectives, antitumor and antineoplastic are synonyms defined as:

Other synonyms of antitumor include anticancer, antitumour.

antitumor (noun)	antineoplastic (noun)
	any of several drugs that control or kill neoplastic cells; used in chemotherapy to kill cancer cells; all have unpleasant side effects that may include nausea and vomiting and hair loss and suppression of bone marrow function

antitumor (adjective)	antineoplastic (adjective)
used in the treatment of cancer	used in the treatment of cancer