Fact 1: Cancer cells divide more often than normal cells, and grow out of control.

Fact 2: Cancer cells, however, grow out of control and develop into a tumor.

Given the two facts above, answer the question "Tumors are a collection of cancer what?" with the following options: 
- harmful
 - mutations
 - cells
 - toxins
 - three
 - Mass
 - oncogenes
 - ovaries


 

   cells      