It might eventually break off and enter the blood stream and be carried to other parts of the body. When it spreads to other parts of the body, it is called metastatic cancer. Most cancer deaths are due to metastatic disease. Cancer is not an infectious or contagious disease like the flu, a common cold, or a bacterial infection. You can't catch it from a patient's handshake or sneeze.
Cancer is really a collection of many different diseases under a single heading.
Some forms of cancer, but not all, are heritable. Some, but not all, forms of cancer are caused by exposure to chemicals, or radiation, or viruses. And, different types of cancer are caused by different genetic and environmental factors. If you suspect that you or someone else might have cancer, consult a physician. A variety of factors determine whether a normal cell will become altered into a tumor cell.