cancer vs metastatic tumor

cancer and metastatic tumor both are nouns.

Word	Noun	Adjective	Verb	Adverb
cancer	Yes	No	No	No
metastatic tumor	Yes	No	No	No

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

cancer: any malignant growth or tumor caused by abnormal and uncontrolled cell division; it may spread to other parts of the body through the lymphatic system or the blood stream
metastatic tumor: a tumor that is malignant and tends to spread to other parts of the body

Other hypernyms of cancer include malignant neoplasm, malignant tumor.

cancer (noun)	metastatic tumor (noun)
any malignant growth or tumor caused by abnormal and uncontrolled cell division; it may spread to other parts of the body through the lymphatic system or the blood stream	a tumor that is malignant and tends to spread to other parts of the body