Basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) are the two most common forms of non-melanoma skin cancer. Both arise primarily from long-term exposure to ultraviolet (UV) radiation, which causes damage to the DNA of skin cells. While sharing this common origin, the two cancers behave differently within the skin, leading to distinct levels of severity and risk.
Understanding the Origins of BCC and SCC
These two cancers are defined by the specific type of skin cell from which they originate within the epidermis. Basal cell carcinoma begins in the basal layer, the deepest part of the epidermis. This layer contains basal keratinocytes, the cells responsible for producing new skin cells.
Basal cell lesions often appear as a shiny, pearly, or translucent bump, sometimes with tiny visible blood vessels, or as a flat, reddish patch similar to eczema. This cancer is characterized by a notably slow growth pattern. Because of this slow growth, BCC is considered a locally invasive tumor that rarely spreads beyond its original site.
In contrast, squamous cell carcinoma arises from the squamous cells, which are flat keratinocytes located closer to the surface of the epidermis. SCC lesions typically present as a firm, scaly, or crusty patch of skin, or as a sore that may bleed and fail to heal. The growth of SCC is generally faster than BCC, allowing it to exhibit a greater capacity for aggressive local behavior.
Comparing Invasiveness and Mortality Risk
The core difference between these two cancers lies in their potential to spread, or metastasize. Basal cell carcinoma is overwhelmingly confined to the original site of development, with a metastatic rate of less than 0.1%. Although it is highly unlikely to spread, an untreated BCC can still cause significant problems by growing deep into the tissue and destroying local structures, such as cartilage and bone.
Squamous cell carcinoma poses a higher systemic risk because it is more likely to metastasize to distant organs or lymph nodes. The metastatic rate for SCC is estimated to be between 2% and 5% overall, making it the more dangerous of the two types. This risk is elevated in specific high-risk scenarios, such as when the lesion is located on the lip, ear, or a non-sun-exposed area.
The potential for SCC to spread is also heightened if the tumor is large, deep, or occurs in a patient who is immunosuppressed. Furthermore, SCC is more likely to involve the nerves, a feature known as perineural invasion, which is associated with increased recurrence and poorer outcomes. Therefore, while both are treatable, SCC requires greater vigilance due to its systemic risk.
Treatment Approaches and Prognosis
The treatment approach for both BCC and SCC primarily focuses on complete removal of the cancerous cells, though the choice of method depends on the tumor’s size, location, and overall risk factors. Standard surgical excision is a common and effective treatment, involving the removal of the tumor along with a margin of healthy surrounding tissue. For low-risk, superficial BCC and SCC in situ, non-surgical options like topical chemotherapy creams or photodynamic therapy may be used.
Mohs micrographic surgery (MMS) is often the preferred approach for both cancer types when treating tumors in cosmetically sensitive areas or for high-risk, recurrent, and aggressive lesions. Mohs surgery involves removing the tumor layer by layer and examining the margins immediately under a microscope until no cancer cells remain, achieving a cure rate exceeding 97% for primary tumors. For patients who cannot undergo surgery, radiation therapy is a successful alternative.
The long-term prognosis and follow-up schedules differ significantly, reflecting the difference in metastatic potential. The 5-year cure rate for SCC following Mohs surgery (about 95.5%) is slightly lower than the rate for BCC (98.7%). SCC patients typically require a more rigorous and frequent follow-up schedule, often involving check-ups every three months during the first year. This intensive surveillance is necessary because SCC has a higher incidence rate of recurrence.