Axillary lymph nodes are located in the armpit (axilla), the hollow area where your upper arm meets your torso. Each armpit contains between 20 and 40 of these small, oval-shaped nodes spread across several distinct groups. They filter fluid draining from your arm, chest wall, upper back, and breast tissue, which is why they play such a central role in breast cancer screening and staging.
The Five Groups and Where They Sit
The nodes in your armpit aren’t clustered in one spot. They’re organized into five groups, each named for the structure it sits near:
- Anterior (pectoral) nodes sit along the lower border of the smaller chest muscle (pectoralis minor), near the front fold of the armpit. These receive most of the lymph drainage from the breast.
- Posterior (subscapular) nodes line the back wall of the armpit, along the lower edge of the shoulder blade muscle. They primarily drain fluid from the upper back and the back of the shoulder.
- Lateral (humeral) nodes run along the outer wall of the armpit, close to the upper arm bone. Fluid from the arm drains here first.
- Central nodes sit in the base, or deepest part, of the armpit. They collect fluid from the anterior, posterior, and lateral groups.
- Apical (terminal) nodes are tucked deep at the very top of the armpit, near the collarbone. They’re the final stop before lymph fluid returns to the bloodstream.
Fluid generally moves in a predictable direction: from the outer groups inward to the central nodes, then upward to the apical nodes. This stepwise flow is why doctors pay close attention to which group is affected when cancer is found.
Levels I, II, and III
Surgeons and radiologists also divide the axillary nodes into three levels based on their relationship to the pectoralis minor, the smaller of the two chest muscles that runs beneath your collarbone area. This system matters most during breast cancer treatment, because it tells surgeons how far cancer cells may have traveled.
Level I nodes sit to the outer side of the pectoralis minor. This level includes the lateral, central, and subscapular groups and is where cancer cells from the breast typically arrive first. Level II nodes are found directly behind the pectoralis minor. Level III nodes sit on the inner side of the muscle, closest to the center of your chest. Cancer reaching Level III means it has traveled through the full chain, which affects staging and treatment decisions.
What They Feel Like and How They’re Checked
During a physical exam, a clinician will ask you to raise your arm and rest your hand behind your head. This position opens the armpit and relaxes the surrounding muscles. Using gentle circular motions, the examiner palpates high in the armpit first, then moves outward along the upper arm, down the chest wall, and inward toward the breastbone. Healthy nodes are usually too small and soft to feel at all.
When a node is palpable, what matters is its size, shape, and texture. A normal axillary lymph node is oval, has smooth edges, and measures less than about 10 millimeters across its short axis. The outer layer (cortex) of a healthy node is thin, typically under 3 millimeters. Nodes that become round, develop a thickened cortex of 3 millimeters or more, or lose their normal inner fat stripe are considered suspicious on ultrasound and may need further evaluation.
Why Axillary Nodes Matter in Breast Cancer
A large share of the lymph fluid from breast tissue drains directly into the anterior axillary nodes. This makes the armpit the most likely first destination for breast cancer cells that begin to spread. The sentinel node, the very first node that receives drainage from a tumor, is almost always located here.
To find the sentinel node during surgery, a surgeon injects a radioactive tracer, a blue dye, or both near the tumor. The dye or tracer travels the same path cancer cells would follow. The surgeon then identifies the stained or radioactive node, removes it, and sends it to a pathologist. If the sentinel node is free of cancer, the remaining axillary nodes are very likely clear as well, which can spare patients a larger surgery.
What Else Drains Into These Nodes
The axillary nodes don’t serve the breast alone. They filter lymph from a wide territory: the entire arm and hand, the upper back and shoulder, the chest wall, and part of the abdominal wall above the navel. That means a swollen node in your armpit doesn’t automatically point to breast cancer. Infections in the hand or arm, skin conditions, recent vaccinations in the upper arm, and even cat scratches can temporarily enlarge these nodes. Swelling that appears suddenly after an illness or vaccination and resolves within a few weeks is a different picture from a painless, hard node that persists or grows over time.