WordNet sense 1 (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):

malignant neoplastic disease

WordNet sense 2 ((astrology) a person who is born while the sun is in Cancer):

crab

WordNet sense 3 (the fourth sign of the zodiac; the sun is in this sign from about June 21 to July 22):

Cancer the Crab

WordNet sense 4 (type genus of the family Cancridae):

genus Cancer