A micrometastasis is a small collection of cancer cells that has been shed from the original tumor and spread to another part of the body through the lymphovascular system. Micrometastases are too few, in size and quantity, to be picked up in a screening or diagnostic test, and therefore cannot be seen with imaging tests such as a mammogram, MRI, ultrasound, PET, or CT scans. These migrant cancer cells may group together to form a second tumor, which is so small that it can only be seen under a microscope. Approximately ninety percent of people who die from cancer die from metastatic disease, since these cells are so challenging to detect. It is important for these cancer cells to be treated immediately after discovery, in order to prevent the relapse (regrowth of the cancer) and the likely death of the patient.
