Skin cancer can spread from its original site to distant parts of the body, including bones. While not all types commonly metastasize to bone, it represents a serious complication, indicating advanced disease. Understanding this process, the types of skin cancer most likely to spread, and the signs and management strategies is important for affected individuals.
The Process of Spread to Bones
The spread of cancer cells from a primary tumor to a new site is known as metastasis. For skin cancer to reach bones, cells detach from the original tumor and typically enter the bloodstream, the primary route for spread. The lymphatic system can also play a role, eventually leading to bloodstream entry.
Once in the bloodstream, these circulating tumor cells travel through the body. Bone marrow, with its rich blood supply and specific molecular environment, is a favorable location for them to settle. Cancer cells then establish themselves, evade the immune system, and grow, forming new tumors within the bone structure. This complex process involves interactions between the cancer cells and the bone microenvironment, leading to either bone destruction or abnormal bone formation.
Which Skin Cancers Are Most Likely to Spread
Melanoma is the most aggressive form of skin cancer and has the highest likelihood of spreading to distant organs, including bones. Bone metastases occur in 11% to 17% of patients with advanced melanoma, though autopsy studies indicate a higher incidence, ranging from 23% to 49%. Bone involvement often occurs as part of widespread metastatic disease, commonly affecting the spine.
Squamous cell carcinoma (SCC) of the skin is less prone to distant metastasis than melanoma but can spread to bones in advanced cases. This risk increases for SCCs that are large, recurrent, located on the head and neck, or occur in individuals with weakened immune systems. The incidence of bone metastasis from SCC is lower, around 0.91% for oral SCC.
Basal cell carcinoma (BCC) is the most common type of skin cancer, but it rarely metastasizes beyond the initial tumor site. In rare, advanced situations, or if left untreated for a long period, BCC can spread to bones. Reported rates are very low, typically ranging from 0.0028% to 0.55%. When it does spread, it often involves the lymph nodes before reaching distant sites like the lungs or bones.
Signs and Diagnosis of Bone Metastasis
Bone metastasis can manifest through several signs and symptoms. Bone pain is the most common, often described as a persistent, gnawing ache that may worsen at night or with activity. This pain can occur at the site of metastasis, such as the spine, pelvis, or long bones. Pathological fractures are another sign, where bones weaken and break easily.
If cancer spreads to spinal bones, it can press on the spinal cord, leading to neurological symptoms like weakness or numbness in the arms or legs, and in severe cases, loss of bladder or bowel control. Cancer-induced bone breakdown can also release high levels of calcium into the bloodstream (hypercalcemia), causing fatigue, nausea, confusion, or dehydration.
Diagnosing bone metastasis involves a combination of imaging techniques. X-rays can reveal bone changes, though more detailed imaging like bone scans, computed tomography (CT) scans, magnetic resonance imaging (MRI), and positron emission tomography (PET) scans are often used. A definitive diagnosis requires a biopsy, where a tissue sample from the suspicious bone area is removed and examined under a microscope.
Treatment and Outlook for Bone Metastasis
The management of skin cancer that has spread to bones focuses on palliative care, aiming to control symptoms, preserve bone function, and improve quality of life. Treatment strategies are individualized based on the skin cancer type, the extent of metastasis, and the patient’s overall health. The primary goals are to alleviate pain, prevent fractures, and manage complications.
Radiation therapy is frequently used to treat bone metastases, as it can effectively reduce pain and help strengthen the affected bone. Systemic therapies, such as chemotherapy, immunotherapy, or targeted therapy, are also used to treat the underlying cancer throughout the body, potentially slowing disease progression.
Pain management is a central component of care, often involving medications, including analgesics and bisphosphonates. Bisphosphonates help to strengthen bones and reduce calcium levels, while radiopharmaceuticals can deliver targeted radiation to bone metastases for pain relief.
In some cases, surgery might be considered to stabilize a bone at risk of fracture or to remove a tumor that is causing severe symptoms or spinal cord compression. While bone metastasis indicates advanced disease, ongoing research and new treatment options continue to improve symptom control and can extend life.