malignant tumor vs neoplasm

malignant tumor and neoplasm both are nouns.

Word	Noun	Adjective	Verb	Adverb
malignant tumor	Yes	No	No	No
neoplasm	Yes	No	No	No

As nouns, neoplasm is a hypernym of malignant tumor; that is, neoplasm is a word with a broader meaning than malignant tumor:

malignant tumor: a tumor that is malignant and tends to spread to other parts of the body
neoplasm: an abnormal new mass of tissue that serves no purpose

Other hypernyms of malignant tumor include tumor, tumour, malignance, malignancy.

malignant tumor (noun)	neoplasm (noun)
a tumor that is malignant and tends to spread to other parts of the body	an abnormal new mass of tissue that serves no purpose