genus Cancer vs Cancer

genus Cancer and Cancer both are nouns.

Word	Noun	Adjective	Verb	Adverb
genus Cancer	Yes	No	No	No
Cancer	Yes	No	No	No

As nouns, genus Cancer and Cancer are synonyms defined as:

genus Cancer (noun)	Cancer (noun)
type genus of the family Cancridae	type genus of the family Cancridae
	the fourth sign of the zodiac; the sun is in this sign from about June 21 to July 22
	a small zodiacal constellation in the Northern Hemisphere; between Leo and Gemini
	(astrology) a person who is born while the sun is in Cancer