An Overview of Micrometastases in Lymph Nodes

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.

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.

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, doctors assume tiny, undetectable metastases 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 doctors 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.

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 doctors 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).

Which treatment you'll need depends on where the metastases are believed to be. Your doctor 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.