Long wave UV-A radiation penetrates deeper in the skin and reaches the lower layer of the epidermis. The DNA of the basal cells that are arranged in this layer get damaged by the radiation. If the natural repairing mechanism does not avoid the propagation of damaged cells, tumor cells develop, which can reproduce uncontrollably.
In addition to exposure by intensive UV-A radiation, a basalioma can develop from benign alterations of the skin (e.g. liver spots, angiomas, keratodermas) or from scars. Additionally some genetic diseases such as xeroderma pigmentosum and Gorlin Goltz syndrome, or arsenic intoxication pose individuals at high risk for developing basal cell carcinoma.
Basal cell carcinoma, at 75-80% of skin cancers found, is the most frequent form of non-melanoma skin cancer. However, metastases arise extremely rarely. About 80% of these tumours appear on the head, face or neck (these areas are considered sun terraces). In only 5% of cases, patients have affected arms and legs.
Generally, the growth of these tumors is rather slow. Yet, basaliomas can grow into lower tissue layers, such as bones.
Both genders are affected equally. The highest frequency of these tumors is found in individuals between ages 65-69 years.
Basal cell carcinomas can be distinguished into 3 different types, according their characteristics.
Nodular cell carcinoma
Solid basaliomas are formed from skin accentuated nodes. The surface of these nodes may appear white and shiny, with small blood vessels often visible. Additionally, it is possible that these lesions become ulcerated, which eventually burst and bleed. With nodular basaliomas, the affected tissue is well delimited from surrounding healthy tissue.
Infiltrative Basal Cell Carcinoma
These basaliomas can be easily confused with scars. Small blood vessels may be visible within these tumors. Different from nodular cell carcinomas, it is difficult to identify the delimitation from the surrounding healthy tissue. This is because these lesions may expand several centimeters into the surrounding healthy tissue. However, this expansion is not visible to the naked eye.
Nodular basal cell carcinomas can also grow deeply into the skin, eroding it (loss of skin tissue). This erosion (“gnawing”) of the skin is commonly known as Ulcus Rodens.
These large lesions often develop from nodes which go untreated. This results in lesions which grow deeply into the skin and eventually scar.