1) Like a cancer 2) Malignant 1) Malign 2) Malignant 
<oncology> A tumour or growth that is malignant (can spread). ... (27 Sep 1997) ... 
Can'cer·ous adjective [ Confer French cancéreux ] Like a cancer; having the qualities or virulence of a cancer; affected with cancer. ' cancerous vices' G. Eliot. [ 1913 Webster] -- Can'cer*ous*ly , adverb -- Can'cer*ous*ness , 
Type: Term Pronunciation: kan′ser-ŭs Definitions: 1. Relating to or pertaining to a malignant neoplasm, or being afflicted with such a process.
[adj] - relating to or affected with cancer 2. [adj] - like a cancer
adjective like a cancer; an evil that grows and spreads; `remorse was cancerous within him`; `pornography is cancerous to the moral development of our children`