The answer to whether breast cancer can be in the armpit, or axilla, is unequivocally yes. The armpit is a common location for breast cancer cells to appear outside of the breast itself. This occurrence is not a separate type of cancer but evidence that the disease has begun to spread from its initial site. Understanding this connection is important because the presence of cancer cells in the armpit significantly influences how the disease is diagnosed, staged, and treated.
The Lymphatic Connection Between Breast Tissue and the Axilla
The anatomical relationship between the breast and the armpit makes the axilla the primary route for breast cancer to spread. The breast is rich with a network of vessels that carry lymph fluid. This fluid flows through the lymphatic system, a circulatory network separate from the blood vessels.
The lymph fluid from the breast tissue drains predominantly into a cluster of small, bean-shaped organs in the armpit called the axillary lymph nodes. These nodes act as filtering stations for the fluid, trapping foreign materials, including cancer cells that have broken away from the primary tumor. Approximately 75% of the lymph fluid from the breast drains into this region, which is why the armpit is often the first site of metastasis.
Once cancer cells reach a lymph node, they can multiply and cause the node to swell, forming a noticeable lump. This involvement indicates that the cancer has progressed beyond the breast tissue itself. The extent to which these nodes are involved is a primary factor used in determining the overall stage of the cancer.
When Cancer Appears Only in the Armpit
In a small number of cases, a person may discover a lump in the armpit confirmed to be breast cancer cells, even though no primary tumor can be found in the breast itself. This rare presentation is referred to as occult breast cancer, or breast cancer of unknown primary. It occurs when the original tumor in the breast is too small to be felt during a physical examination or seen on standard imaging like a mammogram.
This situation poses a diagnostic challenge because the initial presentation is solely the metastatic disease in the axillary nodes. Occult breast cancer accounts for a very small fraction of all breast cancer diagnoses. Even when the primary tumor cannot be identified, the cancer is still treated as breast cancer that has already spread to the lymph nodes.
The focus remains on treating the disease found in the armpit and carefully investigating the breast. Without definitive treatment of the breast tissue, there is a substantial risk for a mass to appear later. Imaging techniques, such as a magnetic resonance imaging (MRI) scan of the breast, often help locate the subtle primary tumor in these cases.
Diagnostic Steps for an Axillary Lump
When a person presents with a suspicious lump in the armpit, the diagnostic process begins with a physical examination. The doctor will check both breasts and the lymph nodes in the armpit and above the collarbone for any swelling or firmness. This initial assessment is followed by imaging tests to visualize the tissue and locate the lump’s origin.
The first line of imaging usually includes a diagnostic mammogram and an ultrasound of both the breast and the axilla. Ultrasound is particularly useful for examining the armpit, as it helps determine if the lump is a solid mass, which is more concerning, or a fluid-filled cyst. If these initial tests are inconclusive, a breast MRI may be ordered for more detailed pictures of the breast tissue.
The definitive test is a biopsy, which involves taking a small tissue sample for lab examination. For an axillary lump, a fine-needle aspiration or core biopsy is typically performed on the enlarged lymph node, often guided by ultrasound. This procedure confirms whether the lump is cancerous and identifies its cellular characteristics to guide treatment planning.
How Armpit Involvement Changes Treatment Strategy
Finding cancer cells in the axillary lymph nodes dictates the overall treatment strategy and prognosis. The presence and number of affected nodes determine the nodal status, which is a component of the cancer’s stage. This information helps oncologists assess the risk of the cancer returning and its potential to spread further.
The surgical management of the armpit nodes typically involves one of two procedures: Sentinel Lymph Node Biopsy (SLNB) or Axillary Lymph Node Dissection (ALND).
Sentinel Lymph Node Biopsy (SLNB)
In an SLNB, a surgeon injects a tracer or dye to identify the first few nodes that drain the tumor—the sentinel nodes. If these sentinel nodes are clear of cancer, no further lymph nodes are usually removed. This approach minimizes complications like swelling in the arm.
Axillary Lymph Node Dissection (ALND)
If the sentinel nodes contain cancer, or if initial imaging suggests extensive disease, a more comprehensive procedure called ALND may be performed. ALND involves removing a larger number of lymph nodes from the armpit for examination. However, recent clinical trials have shown that for patients with only one or two positive sentinel nodes who are receiving breast-conserving surgery and radiation, ALND can often be avoided.
The final decision on axillary surgery directly impacts subsequent non-surgical treatments. A positive nodal status often necessitates more aggressive systemic therapy, such as chemotherapy or targeted drug therapy, to treat potential microscopic disease throughout the body. Radiation therapy may also be directed at the armpit region to reduce the risk of local recurrence.