An Overview of Micrometastases in Lymph Nodes

These cancer cells are the reason for adjuvant therapy

Micrometastases are a small collection of cancer cells that have been shed from the original tumor and spread to another part of the body through the blood or lymph nodes. They group together and form a second tumor that's too small to be seen with imaging tests such as a mammogram or MRI, and can only be seen under a microscope.

Traveling tumor cells
vitanovski / iStock

If you're having a sentinel node biopsy, your breast surgeon or oncologist may have mentioned micrometastases. They are extremely important in almost any type of cancer and are the reason behind adjuvant therapy—add-on treatment given to help prevent recurrence.

In cancer, the worst damage isn't usually caused by the primary cancer (for example, in the breast). It's when cancer spreads (metastasizes) to other regions of the body. Roughly 90% of cancer deaths are because of metastatic disease.


Micrometastases are defined as clusters of cancer cells that are between 0.2 mm and 2.0 mm in diameter. Any smaller clusters are called isolated tumor cells.

When cancer first spreads and forms micrometastases, the only way to detect them is to remove the tissue where they are located and look at slices under a microscope. That's what happens in a lymph node biopsy.

However, it's impossible to remove and examine every lymph node. It is also impossible to remove other essential organs from the body to look for spreading. Therefore, healthcare providers assume tiny, undetectable metastases may exist outside of the breast(s) and lymph nodes when:

  • A tumor is of a particular size
  • There's evidence cancer has spread to the lymph nodes

When there isn't evidence of lymph node involvement on exam or ultrasound, a sentinel lymph node biopsy has become a standard of care. In this procedure, blue dye is injected into the tumor and allowed to travel so that it stains other cancer cells. When cancer spreads from tumors, it often spreads to lymph nodes in a predictable pattern, and the dye can help healthcare providers see that pattern and identify micrometastases via imaging.

By doing a biopsy of the sentinel node or nodes—the first few nodes that cancer would travel to—many women are spared a full axillary lymph node dissection (removal of many or all of the lymph nodes in the armpit). Since full axillary dissection can result in complications such as lymphedema, sentinel node biopsy is considered a safer option.

Research is ongoing to determine the significance of micrometastases in the sentinel node. Thus far, it's known that macrometastases (metastases larger than 2.0 mm) worsen the prognosis of the disease, as do micrometastases in the sentinel node.

Meanwhile, women who have isolated tumor cells in the sentinel node do not have a prognosis any worse than a woman with no evidence of metastases to the sentinel node.

Having this information can help healthcare providers understand which women will need a full axillary lymph node dissection, and which should consider adjuvant treatment of their breast cancer.


Adjuvant chemotherapy or adjuvant radiation therapy 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 chemotherapy).

For hormone receptor positive disease, hormone treatments such as tamoxifen or letrozole can be as important as chemotherapy for treating metastases.

Which treatment you'll need depends on where the metastases are believed to be. Your healthcare provider may recommend both chemotherapy and radiation, as well.

Breast cancers that have begun to travel to the lymph nodes are more likely to spread to other regions of the body. Therefore, it's important to be aggressive with treatment.

Was this page helpful?
7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Gómez-Cuadrado L, Tracey N, Ma R, Qian B, Brunton VG. Mouse models of metastasis: progress and prospectsDis Model Mech. 2017;10(9):1061-1074. doi:10.1242/dmm.030403

  2. Zahoor S, Haji A, Battoo A, Qurieshi M, Mir W, Shah M. Sentinel Lymph Node Biopsy in Breast Cancer: A Clinical Review and UpdateJ Breast Cancer. 2017;20(3):217-227. doi:10.4048/jbc.2017.20.3.217

  3. Carretta A. Clinical value of nodal micrometastases in patients with non-small cell lung cancer: time for reconsiderationJ Thorac Dis. 2016;8(12):E1755-E1758. doi:10.21037/jtd.2016.12.83

  4. Manca G, Tardelli E, Rubello D, et al. Sentinel lymph node biopsy in breast cancer: a technical and clinical appraisal. Nucl Med Commun. 2016;37(6):570-576. doi:10.1097/MNM.0000000000000489

  5. Henke G, Knauer M, Ribi K, et al. Tailored axillary surgery with or without axillary lymph node dissection followed by radiotherapy in patients with clinically node-positive breast cancer (TAXIS): study protocol for a multicenter, randomized phase-III trial. Trials. 2018;19(1):667. doi:10.1186/s13063-018-3021-9

  6. Apple SK. Sentinel Lymph Node in Breast Cancer: Review Article from a Pathologist's Point of ViewJ Pathol Transl Med. 2016;50(2):83-95. doi:10.4132/jptm.2015.11.23

  7. Lee KB, Shim SH, Lee JM. Comparison between adjuvant chemotherapy and adjuvant radiotherapy/chemoradiotherapy after radical surgery in patients with cervical cancer: a meta-analysisJ Gynecol Oncol. 2018;29(4):e62. doi:10.3802/jgo.2018.29.e62

Additional Reading