One trademark of cancerous cells is their ability to spread throughout the body. Primary cancer can begin to grow within the brain, the feet or anywhere in between. Wherever this primary cancer originates, it typically forms a mass, also known as a tumor. Once the cancer cells begin to migrate away from the tissue or organ where they were born, the condition is referred to as metastasis -- this is almost always when the cancer becomes especially life-threatening.
However, some small groups of cancerous cells can survive in the body without spreading or forming tumors for many years. A group of cells that hasn't invaded any additional organ or tissue is referred to as carcinoma in situ. In some instances, carcinoma in situ may be just as hard to spot as a single cancer cell, but some carcinomas, including those affecting the skin, the cervix and the breast, often can be found and treated before they become dangerous.
One particularly common form of carcinoma in situ is known as ductal carcinoma in situ (DCIS), which involves cancer cells that grow within the milk duct of a human breast. While DCIS itself is not life-threatening, it has the potential to develop into invasive breast cancer. When DCIS is detected in the course of a standard mammogram, physicians usually recommend a course of treatment involving radiation therapy and limited surgery [source: Mayo Clinic] When a more advanced cancerous growth is present, a full mastectomy is a common surgical option, but in the case of DCIS, more patients undergo a lumpectomy, in which only a small portion of the breast tissue is removed [source: Mayo Clinic].
Cervical carcinoma in situ can also be detected during a routine Pap smear or other method of cervical screening. As is the case with DCIS, cervical carcinoma in situ is not itself dangerous, but it is usually treated to prevent development of invasive cancer in the future [source: Cancer Research UK].
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