What Exactly are Micrometastases and What is Their Significance?

What do Micrometastases Mean in a Sentinel Lymph Node Biopsy Sample?

What are micrometastases and what is their significance?. Istockphoto.com/Stock Photo©vitanovski

Definition: Micrometastases

Micrometastasis is a small collection of cancer cells that have been shed from the original tumor and spread to another part of the body. They cannot be seen with any imaging tests such as a mammogram, MRI, ultrasound, PET, or CT scans. These migrant cancer cells may group together and form a second tumor, which is so small that it can only be seen under a microscope.

Significance of Micrometastases

The presence of micrometastases is very significant, as it's felt that tumors that metastasize and grow apart from the original tumor begin as these small clusters of cancer cells.

Micrometastases are the reason for treatments known as adjuvant chemotherapy or adjuvant radiation therapy.  These are treatments that are used after a primary tumor has been removed to "clean up" any micrometastases near the origin of the tumor (via radiation) or anywhere in the body where they may have traveled (via radiation.)

Micrometastases vs Isolated Tumor Cells

When used in the setting of most cancers, micrometastases refer to these cells that are suspected to have traveled (metastasized) from the tumor, but are not detectable by the imaging studies we currently have available.

A further classification of these small areas of spread is of use in talking about sentinel node biopsies with breast cancer.  In that setting, micrometastases are defined as clusters of cancer cells that are between 0.2 mm (millimeters) in diameter and 2.0 mm in diameter.  In contrast, "isolated tumor cells" are clusters of cancer cells that are smaller yet - less than 0.2 mm in diameter.

Micrometastases in a Sentinel Lymph Node Biopsy

For women with breast cancer who do not have evidence of lymph node involvement on exam or ultrasound, sentinel lymph node biopsy has become a standard of care.  In this procedure, blue dye (that is also tagged so it can be detected radiographically) is injected into the tumor and allowed to travel.

  When cancer spreads from tumors it often spreads to lymph nodes in a predictable pattern.

By doing a biopsy of the sentinel node or nodes - the first few nodes that a cancer would travel to - many women are spared a full axillary dissection (removal of all or many of the lymph nodes in the armpit.)  Since full axillary dissection can result in complications such as lymphedema, this procedure may spare some women having the full axillary dissection if cancer cells have not traveled to the sentinel node.

Research is ongoing to determine the significance of micrometastases in the sentinel node - by definition, this would mean clusters of tumor cells which are between 0.2 mm and 2.0 mm in diameter.

Thus far it's known that macrometastases (metastases that can be detected easily under a microscope) worsen the prognosis of the disease.  It's also been found that the prognosis of women who have micrometastases to the sentinel node have a poorer prognosis than women who do not have any evidence of tumor having spread to these lymph nodes.  In contrast, women who have isolated tumor cells in the sentinel node (by definition an area of tumor cells less than 0.2 mm in diameter) do not have a prognosis any worse than a woman with no evidence of metastases to the sentinel node.

Having this information can help researchers learn further which women will need a full axillary lymph node dissection, and which women should be considered highly for adjuvant treatment of their breast cancer.

Pronunciation: MY-kroh-meh-TAS-tuh-sis

Common Misspellings: micrometastisis

Examples: During a sentinel lymph node biopsy, the lymph nodes that are removed will be tested for micrometastasis. If a lymph node is found to contain micrometastasis, it is said to be positive, and this information affects your diagnosis, staging, and treatment plan.


Dominici, L.  Breast Cancer Axillary Staging: Much Ado About Micrometastatic Disease.  Journal of Clinical Oncology.  2015.  59:2303.

Harlow, S., and D. Weaver.  Diagnosis, staging and the role of sentinel lymph node biopsy in the nodal evaluation of breast cancer.  UpToDate.  Updated 01/06/16.  http://www.uptodate.com/contents/diagnosis-staging-and-the-role-of-sentinel-lymph-node-biopsy-in-the-nodal-evaluation-of-breast-cancer

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