Disambiguation of cancer

I was confused by the use of the word cancer so differently in at least 4 unrelated definitions: a crab (in Russian this word refers to a crayfish), malignant disease, constellation, and sign of zodiac. I was wondering what could be the connection between for example a crab and malignant disease, and I'll quote directly the answer from Answers.com : "The word cancer is Latin for "crab". Its use for cancer goes back to Hippocrates (ca. 460 BC - ca. 370 BC) (http://en.wikipedia.org/wiki/Cancer#History), who is said to have derived it from the appearance of the cut surface of a solid malignant tumour, with "the veins stretched on all sides as the animal the crab has its feet, whence it derives its name".

Read more: http://wiki.answers.com/Q/Why_is_the_disease_cancer_called_cancer#ixzz18s2Ol1Pa"