Breast cancer involves genetic mutations that make breast cells proliferate rapidly, evade normal cell death and form tumors. During breast cancer progression, tumor cells invade tissues in and around the breast, and eventually travel to distant tissues around the body. Nodal micrometastasis refers to breast cancer that spreads to the lymph nodes which make up a part of the immune system.
Sentinel Node Micrometastasis
Sentinel node micrometastasis refers to cancer colonization of the first, or sentinel, lymph node in cancer development, according to the National Cancer Institute. Cancer cells first invade the sentinel lymph node, leading to node enlargement and additional cancer growth. Since the sentinel growth is connected to other lymph nodes by a system of lymphatic vessels, colonization of the sentinel node can indicate the presence of cancer in other lymph nodes around the affected breast. Doctors perform sentinel lymph node biopsies to remove and examine the first site of the cancer's spread. Patients positive for sentinel lymph node micrometastases require additional testing to determine the extent of breast cancer spread.
Axillary Node Micrometastasis
Once the cancer has spread to a sentinel node, the patient may develop axillary node micrometastasis. The axillary lymph nodes are found around the breast tissue as well as under the arms, and they connect to the sentinel node through a network of lymph vessels. As breast cancer grows within the axillary lymph nodes, the structures enlarge with cancer cells and eventually become matted together. As a result, patients with axillary node micrometastases may notice a lump under the arm corresponding to matted lymph nodes. Axillary lymph node swelling can indicate the presence of relatively advanced breast cancer, and MedlinePlus recommends that women who notice a lump under the arm seek immediate medical attention.
Internal Mammary Node Micrometastasis
Often, an early site of nodal micrometastasis is within the mammary gland, or breast, itself, and one of the lymph nodes within the breast may or may not be a sentinel node. Each breast contains a series of lymph nodes within the breast tissue, and cancer growth within the breast can lead to the colonization of these nearby lymph nodes during cancer development. The extent of internal mammary node micrometastasis in the breast can help doctors assess the severity of the cancer: around 30 percent of women with axillary node micrometastases also develop internal mammary node micrometastases, according to the "British Medical Journal." Most internal mammary node metastases are removed during breast cancer surgeries, so these micrometastases present only a small risk of breast cancer recurrence after treatment.
