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, MRI, ultrasound, PET, or CT scans. They can only be seen under a microscope.

If you're having a sentinel node biopsy, your breast surgeon or oncologist may have mentioned micrometastases. Micrometastases are extremely important with almost any type of cancer and are the reason behind what is called "adjuvant therapy."

In cancer, the worst damage isn't usually caused by the primary cancer (in the breast, lungs, etc.)—it's when cancer spreads, metastasizes, to other regions of the body. Roughly 90 percent 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. Clusters of cancer cells that are smaller than that 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 of the tissue under the microscope. That's what happens in a lymph node biopsy.

However, it's impossible to remove every lymph node. It is also impossible to remove other essential organs from the body to look for spreading.

Therefore, when a tumor is of a particular size or if it has spread to lymph nodes, doctors assume tiny metastases exist elsewhere in the body but cannot yet be detected.

For women with breast cancer who do not have 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 (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 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 lode 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, as well. Therefore, it's important to be aggressive with treatment.