Micrometastases are small collections of cancer cells that have been shed from a cancerous tumor and have spread to another part of the body through the blood or lymph nodes. Micrometastases can then form a second tumor that’s too small to be seen on imaging tests, such as a mammogram or MRI (magnetic resonance imaging), and can only be seen under a microscope.

If you have had 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—treatment given after surgery to help prevent a recurrence of cancer.

This article will review micrometastases in breast cancer and how they are diagnosed and treated.

Diagnosis

Micrometastases are defined as clusters of cancer cells that are between 0.2 millimeters and 2 millimeters (mm) in diameter. Any smaller clusters are called isolated tumor cells.

In a curable cancer, the primary cancer (for example, in the breast) is surgically removed. This is done to treat the cancer and prevent it from spreading. When cancer spreads (metastasizes) to other regions of the body, it is not considered curable.

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. This is known as a lymph node biopsy.

However, it’s impossible to remove and examine every lymph node and organ in the body to check for small cancer cells. Oncologists 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 is done. In this procedure, blue dye is injected into the breast and allowed to travel so that it reaches the nearby lymph nodes. When cancer spreads from tumors, it often spreads to lymph nodes in a predictable pattern. The dye can help healthcare providers see that pattern and identify where to look for micrometastases.

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 removing all the nodes can result in complications such as lymphedema, a sentinel node biopsy is considered a safer option.

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

Research is ongoing to determine the significance of micrometastases in the sentinel node. Currently, it’s known that macrometastases (metastases larger than 2 mm) worsen the prognosis of the disease, as do micrometastases in the sentinel node.

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

Treatment

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.

Summary

Micrometastases are microscopic cancer cells that have escaped from the original tumor. These cells can be too small to see on imaging tests.

There are some characteristics of breast cancer, such as size and the presence of cancer in lymph nodes, that make micrometastasis more likely. A procedure called a sentinel node biopsy can help healthcare providers know where to look for micrometastases. They can be treated with chemotherapy or radiation.

Frequently Asked Questions

  • How long does it take for breast cancer to metastasize?
  • This is a question that does not have a clear-cut answer. Researchers are still discovering the ways metastatic disease happens in breast cancer. It is possible that cancer cells can remain in the body for many years before starting to grow.
  • What is the difference between micrometastasis and macrometastasis?
  • The difference is the size of the cells. Micrometastases are 0.2–2 mm in size, and macrometastases are greater than 2 mm in size.
  • Are micrometastases lymph node-positive?
  • If micrometastases are present in a lymph node, then it is positive. However, if only micrometastases are present, a full lymph node removal surgery may not be needed.
  • What is the survival rate when breast cancer spreads to lymph nodes?
  • The survival rate is described in terms of the percentage of people who are alive five years after a cancer diagnosis. For breast cancer that has spread to lymph nodes, the five-year survival rate is 86%.

This is a question that does not have a clear-cut answer. Researchers are still discovering the ways metastatic disease happens in breast cancer. It is possible that cancer cells can remain in the body for many years before starting to grow.

The difference is the size of the cells. Micrometastases are 0.2–2 mm in size, and macrometastases are greater than 2 mm in size.

If micrometastases are present in a lymph node, then it is positive. However, if only micrometastases are present, a full lymph node removal surgery may not be needed.

The survival rate is described in terms of the percentage of people who are alive five years after a cancer diagnosis. For breast cancer that has spread to lymph nodes, the five-year survival rate is 86%.