Shoulder pain is a common concern for people who have received treatment for breast cancer. Up to 60% of survivors may experience some degree of shoulder discomfort. The connection between breast cancer and shoulder pain is often indirect, arising most frequently as a byproduct of necessary surgical and radiation treatments. While the pain is usually a localized, musculoskeletal side effect, it can occasionally be a warning sign requiring immediate medical evaluation. Understanding the difference between these causes is important for proper management.
Treatment-Related Causes of Shoulder Pain
A significant portion of shoulder issues following breast cancer treatment are related to physical changes in the chest, armpit, and surrounding tissues. Surgical procedures, particularly those involving the removal of lymph nodes, can lead to a condition called Axillary Web Syndrome (AWS), or “cording.” This involves the formation of thick, ropelike scar tissue under the skin, often running from the armpit down the arm, which restricts movement and causes tightness and pain when the arm is extended.
Surgery in the axilla can also cause general stiffness and a reduced range of motion, sometimes due to nerve damage or protective posturing after the procedure. Over time, this restricted movement can lead to secondary issues like shoulder impingement or rotator cuff problems. Furthermore, disruption of the lymphatic system can result in lymphedema, which is the swelling of the arm and chest wall. This increased volume and weight places stress on the shoulder joint and surrounding nerves, contributing to chronic shoulder pain.
Radiation therapy can introduce another source of shoulder dysfunction through radiation fibrosis. This process causes tissues to become stiff, less elastic, and scarred, restricting the movement of muscles and connective tissue around the shoulder joint over a period of months or years. The resulting tissue changes alter the shoulder’s natural biomechanics, leading to pain and reduced function. These treatment-related causes are localized consequences of therapy and are not indications of cancer recurrence or spread.
When Shoulder Pain Signals Disease Progression
While most shoulder pain is benign, patients are concerned whether the discomfort signals disease progression, specifically the spread of cancer cells. Breast cancer frequently metastasizes to the bones, including the ribs, spine, or humerus, which are components of the shoulder girdle. When cancer settles in these areas, it causes persistent, deep, aching pain unlike typical musculoskeletal soreness.
This pain is often described as mechanical, worsening with movement, but characteristically persists or intensifies at night, disrupting sleep and failing to be relieved by rest or standard over-the-counter pain medication. The tumor growth or resulting structural degradation of the bone tissue irritates local nerves, leading to this unrelenting discomfort. Pain can also be referred to the right shoulder if the cancer has spread to the liver, as some nerves near the liver attach near the shoulder blade.
The presence of systemic symptoms alongside shoulder pain should prompt an immediate call to the oncology team. These “red flag” symptoms include unexplained weight loss, persistent fatigue, or the sudden onset of a bone fracture. New or worsening pain patterns, especially those that feel deep, constant, and are not clearly related to physical activity, should be evaluated to rule out bone metastasis or nerve compression near the brachial plexus.
Evaluation and Therapeutic Strategies
Determining the source of shoulder pain requires a comprehensive diagnostic process beginning with a physical examination to assess range of motion and strength. The physician differentiates between pain that is clearly musculoskeletal, like rotator cuff tendinitis, versus pain that suggests a deeper, structural issue. If cancer spread is a concern, imaging studies play a definitive role in the diagnosis.
Radiographic tools like X-rays, magnetic resonance imaging (MRI), or computed tomography (CT) scans visualize the shoulder joint and surrounding soft tissues to identify musculoskeletal causes. To look for bone metastasis, a bone scan or a PET scan may be used to detect increased metabolic activity suggesting the presence of cancer cells. Once the cause is identified, the management plan is tailored to the specific diagnosis.
For treatment-related issues like stiffness, cording, and restricted range of motion, physical therapy (PT) is the cornerstone of rehabilitation. A PT program incorporates stretching, strengthening exercises, and specific techniques like soft-tissue mobilization to address scar tissue and restore normal shoulder mechanics. If lymphedema is contributing to the pain, manual lymphatic drainage (MLD) performed by a certified lymphedema therapist helps reduce swelling and pressure on the surrounding nerves and joints. Medical management for non-cancerous pain often includes non-steroidal anti-inflammatory drugs (NSAIDs) or targeted steroid injections to manage inflammation. Patients are encouraged to maintain an active range of motion and report any persistent or changing pain patterns to their care team.