Basal cell carcinoma (BCC) represents the most common form of skin cancer, typically appearing as abnormal skin growths, bumps, or sores that are slow-growing and often successfully treated with localized therapies. While this type of cancer is highly prevalent, metastatic basal cell carcinoma is a rare, advanced form where the cancer spreads beyond its original site. This progression is unusual, occurring in less than 1% of all BCC cases.
What is Metastatic Basal Cell Carcinoma?
Basal cell carcinoma originates from the basal cells in the outer layer of the skin, the epidermis, and commonly presents as a shiny or translucent bump, or a scaly flat patch. These lesions often appear on sun-exposed areas like the head and neck. In most cases, BCC grows slowly and tends to invade only nearby tissues if left untreated.
Metastatic basal cell carcinoma occurs when cancer cells break away from the original tumor and travel through the body’s systems, typically via the lymphatic system or the bloodstream, to distant parts of the body.
Once BCC cells enter these systems, they can establish new tumors in other locations. The most common sites for this distant spread include regional lymph nodes, lungs, and bones.
Factors Contributing to Metastasis
Several factors can increase the likelihood of basal cell carcinoma developing into its metastatic form. The size of the primary tumor plays a significant role; lesions larger than 2 centimeters in diameter are associated with a higher risk of metastasis. This risk further increases for tumors exceeding 5 cm, with a 25% incidence, and rises to 50% for tumors larger than 10 cm.
The anatomical location of the primary tumor also influences its metastatic potential, with lesions on the head and neck, especially around the eyes, nose, or ears, having a higher propensity for spread. Large BCCs, commonly occurring on the trunk, can also be aggressively destructive.
Certain aggressive histological subtypes of BCC, such as infiltrative, micronodular, sclerosing, and basosquamous/metatypical cell carcinomas, are more likely to metastasize than common types like nodular or superficial BCC. A history of multiple recurrences, incomplete initial treatment, or prior radiation therapy for BCC can also increase the risk of metastasis. A weakened immune system, such as in transplant patients, can elevate the risk of BCC spreading.
Identifying Symptoms and Diagnosis
The symptoms of metastatic basal cell carcinoma vary depending on where the cancer has spread within the body. If the cancer has reached the lymph nodes, patients might notice swelling or lumps in those areas. When BCC metastasizes to the lungs, symptoms can include a persistent cough or shortness of breath.
If the cancer spreads to the bones, it can cause localized pain, increased risk of fractures, or elevated calcium levels in the blood (hypercalcemia).
Diagnosing metastatic BCC involves a comprehensive approach. A physical examination by a dermatologist is the initial step to assess suspicious skin lesions and nearby lymph nodes. If metastasis is suspected, imaging techniques are employed to detect distant spread, including CT scans for bone and organ involvement, MRI scans for soft-tissue and nerve spread, and PET scans to locate metastatic sites. A definitive diagnosis requires a biopsy of suspicious lesions or enlarged lymph nodes, where tissue samples are examined under a microscope to confirm the presence of cancer cells.
Treatment and Management
Treatment for metastatic basal cell carcinoma is often complex, requiring a multidisciplinary approach tailored to each patient’s specific situation. The goal is to control the disease, manage symptoms, and improve quality of life. Surgical resection may be an option if the metastases are localized and can be completely removed, although this is less common for widespread disease.
Radiation therapy is frequently used for local control of tumors or to alleviate symptoms, such as pain from bone metastases. For more widespread or advanced cases, systemic therapies are employed to target cancer cells throughout the body. Chemotherapy, while an older approach, can still be considered, sometimes in combination with other agents.
Targeted therapies, particularly Hedgehog pathway inhibitors like vismodegib and sonidegib, are important. These drugs work by blocking the Hedgehog signaling pathway, which is abnormally active in most BCCs and drives their growth. These inhibitors can reduce tumor size and may lead to complete regression in some patients.
Immunotherapies, specifically PD-1 inhibitors such as cemiplimab, are another class of systemic treatment. These drugs work by enhancing the body’s immune response against cancer cells. Cemiplimab is approved for advanced BCC in patients who have either not responded to or cannot tolerate Hedgehog pathway inhibitors. The choice of systemic therapy depends on factors like prior treatments and the patient’s overall health.
Prognosis and Living with Metastatic BCC
The prognosis for metastatic basal cell carcinoma is generally poorer than for localized BCC, but it can vary based on factors such as the extent of spread, the patient’s response to treatment, and overall health. Advancements in systemic therapies have changed the outlook for some patients.
Patients with regional metastases, such as in lymph nodes, often have a more favorable prognosis compared to those with distant metastases to organs like the lungs or bones. For instance, the 5-year survival rate for nodal metastatic BCC can be around 89.3%, while for distant metastatic BCC, it may be closer to 61.0%.
Ongoing monitoring and follow-up care are important for managing metastatic BCC, as recurrence is possible even after successful treatment. Supportive care focuses on managing symptoms and maintaining the patient’s quality of life throughout the treatment journey. This approach helps improve outcomes for individuals facing this rare form of cancer.