Cancer cells stay within the body tissue from which they have developed — for instance, the lining of the bladder or the breast ducts. Doctors call this superficial cancer growth or carcinoma in situ.
The cancer cells grow and divide to create more cells and eventually, it will form into a tumor. A tumor may contain millions of cancer cells.
In addition, every single body tissue has a layer (a membrane) that keeps the cells of the tissue inside. This is the basement membrane. Cancer cells can break through this membrane. If this happens, the cancer is invasive.
