Shoulder pain is common, often from muscle strains, injuries, or arthritis. While most discomfort resolves with rest or basic treatment, cancer can rarely cause shoulder pain. Understanding how cancer might cause this pain and recognizing specific warning signs can help individuals know when to seek medical attention.
Mechanisms of Pain
Cancer can cause shoulder pain through several distinct mechanisms, each involving different interactions with the body’s tissues.
Direct tumor growth, where a mass develops within or near the shoulder joint, can exert pressure on surrounding structures like bones, muscles, or nerves. This leads to localized pain or discomfort and can disrupt joint function.
Metastasis, the spread of cancer, frequently affects bones. Cancer cells establishing in bones like the humerus, scapula, ribs, or spine can cause bone destruction and weakening. This leads to significant pain and increases the risk of pathological fractures.
Nerve compression or invasion is another mechanism, especially for tumors in the upper chest or neck. Pancoast tumors, a type of lung cancer at the lung’s apex, can directly invade or compress the brachial plexus. This nerve network controls sensation and movement in the shoulder, arm, and hand, causing pain that radiates down the arm, numbness, or weakness.
Referred pain occurs when discomfort from an internal organ is felt in a different body part, such as the shoulder, due to shared nerve pathways. For instance, irritation of the diaphragm from issues with organs like the liver or spleen can result in pain felt in the right or left shoulder. Lung tumors can also cause referred pain in the shoulder area.
Paraneoplastic syndromes are rare conditions triggered by the body’s immune response to cancer. The immune system may produce substances that affect distant healthy tissues, including nerves or muscles. This can result in symptoms like pain, weakness, or neurological issues in areas like the shoulder, even without the physical presence of cancer.
Specific Cancers and Shoulder Pain
Certain types of cancer are more frequently associated with shoulder pain due to their common patterns of growth or metastasis. Lung cancer, especially Pancoast tumors at the top of the lung, often cause pain in the shoulder and arm by affecting the nearby brachial plexus.
Breast cancer can also lead to shoulder pain, primarily through its tendency to metastasize to bones. Cancer cells can spread from the breast to bones in the shoulder girdle, such as the humerus or scapula, or to the spine, causing localized bone pain.
Cancers that originate in the bone marrow, such as multiple myeloma and lymphoma, can cause widespread bone pain, including in the shoulder. Multiple myeloma, a cancer of plasma cells, can lead to lesions in bones throughout the body, while lymphoma can also affect bone, resulting in discomfort and structural weakness.
Cancers of the liver or gallbladder can present with referred pain in the right shoulder due to shared nerve pathways with the diaphragm and shoulder area. This pain is perceived in the shoulder even though the problem originates elsewhere.
Many types of cancer have a propensity to spread to bone, which can include the bones of the shoulder. Prostate, kidney, thyroid, and colon cancers are among those that commonly metastasize to bone. When these secondary tumors develop in the humerus, scapula, or clavicle, they can cause significant and persistent shoulder pain.
Recognizing Warning Signs
Distinguishing cancer-related shoulder pain from common causes involves recognizing specific “red flag” symptoms. One indicator is persistent pain that does not improve with rest, physical therapy, or conventional pain relievers. Unlike typical musculoskeletal pain, cancer-related pain may continue or worsen despite these efforts.
Pain that is worse at night or when lying down is another concerning sign. This type of pain often feels unrelated to movement or activity and can significantly disrupt sleep. Common shoulder issues, such as rotator cuff injuries, usually cause pain that intensifies with specific movements or activities.
Unexplained weight loss, persistent, overwhelming fatigue not relieved by rest, and unexplained fevers or drenching night sweats are systemic symptoms that can accompany various cancers. These can signal an underlying malignancy.
Shoulder pain that develops without any obvious trauma, injury, or repetitive strain is another reason for concern. Most common shoulder pains can be traced back to a specific event or activity. Pain that appears spontaneously without such a history warrants further investigation.
Neurological symptoms like numbness, tingling, weakness, or loss of function in the arm or hand can indicate nerve compression or invasion by a tumor. These often accompany shoulder pain when brachial plexus nerves are affected. Any new, unexplained lump or mass in the shoulder or armpit area also warrants immediate medical attention.
The Importance of Medical Consultation
Self-diagnosis of shoulder pain is misleading; professional medical evaluation is essential to determine the cause. Any persistent, unexplained, or worsening shoulder pain, especially with warning signs, requires prompt medical assessment. Delaying evaluation can have consequences for any underlying condition.
A healthcare provider can conduct a thorough examination, order appropriate diagnostic tests like imaging or blood tests, and determine the precise cause. While cancer is a rare cause of shoulder pain, it is important not to ignore concerning symptoms. Early diagnosis is important for effective treatment outcomes.