Basal Cell Carcinoma (BCC) is the most frequently diagnosed form of skin cancer. It originates from the basal cells in the deepest layer of the epidermis, which are responsible for continuously producing new skin cells. While BCC is known for its slow growth and localized behavior, leaving it untreated allows the tumor to progress beyond the skin’s surface. This progression shifts the cancer from a simple skin lesion to a complex problem involving deep tissue destruction and functional loss.
Local Progression and Tissue Destruction
When left unaddressed, BCC lesions expand radially and vertically within the superficial skin layers and adjacent subcutaneous fat. The initial small, pearly papule gradually enlarges, and the surface integrity is compromised as the tumor cells proliferate. This growth often leads to the development of a central ulceration, commonly described as a “rodent ulcer,” characterized by a depressed center and a raised, rolled border.
Untreated BCC typically presents with persistent crusting and frequent, minor bleeding, often triggered by slight trauma due to the tumor’s delicate blood vessels. This destructive growth causes significant cosmetic disfigurement as the lesion increases in size. A lesion that initially required a small, straightforward excision eventually demands extensive surgical removal and complex reconstructive surgery. Delaying treatment transforms a minor medical procedure into a major surgical challenge.
Functional Impairment Through Deep Invasion
The most serious consequence of untreated BCC is its capacity for deep, local invasion, which compromises nearby structures and causes functional impairment. This advanced disease is particularly concerning in high-risk anatomical areas of the face, such as the nose, ears, and around the eyes. In these locations, there is very little soft tissue separating the skin from underlying cartilage, bone, and nerves.
A tumor near the eye can invade the orbit, potentially causing permanent vision loss or requiring the removal of the eye (enucleation) for complete cancer clearance. BCCs on the nose or ear that progress can destroy the underlying cartilage, leading to structural collapse and profound disfigurement. Aggressive subtypes, such as infiltrative and morpheaform BCC, are especially prone to this deep penetration.
The cancer can also spread along nerve pathways, a process known as perineural invasion, indicating advanced disease and high recurrence risk. Invasion of facial nerves can result in motor deficits, including localized muscle weakness or complete facial paralysis. If the tumor reaches the bone, particularly the skull or facial bones, the required surgical intervention becomes far more invasive and debilitating, often involving specialized head and neck surgical teams.
The Rare Risk of Metastasis
While the primary threat from untreated BCC is local destruction, the cancer carries a small, real risk of metastasis, meaning spread to distant sites in the body. BCC is unique among common cancers for its extremely low metastatic rate, documented to be less than 1% of all cases. This systemic spread typically occurs only in cases of prolonged neglect or in tumors that exhibit specific high-risk features.
Factors that increase this rare risk include a large primary tumor size, often exceeding two centimeters in diameter, and aggressive histological subtypes like morpheaform or infiltrative BCC. Immunosuppression or a history of radiation therapy can also elevate the potential for systemic spread. When metastasis occurs, cancer cells most commonly travel to the regional lymph nodes first, but distant spread to organs such as the lungs and bones is possible. Once BCC metastasizes, the prognosis changes significantly, becoming much more difficult to treat and associated with a poorer long-term outlook.