Basal-cell carcinoma (BCC), also known as basal-cell cancer, basalioma, or rodent ulcer, is the most common type of skin cancer. It often appears as a painless, raised area of skin, which may be shiny with small blood vessels running over it. It may also present as a raised area with ulceration. Basal-cell cancer grows slowly and can damage the tissue around it, but it is unlikely to spread to distant areas or result in death. Risk factors include exposure to ultraviolet light (UV) (usually from sun exposure), having lighter skin, radiation therapy, long-term exposure to arsenic, and poor immune-system function. Exposure to UV light during childhood is particularly harmful. Tanning beds have become another common source of ultraviolet radiation. Whether sunscreen affects the risk of basal-cell cancer remains unclear. Diagnosis often depends on skin examination, confirmed by tissue biopsy. Treatment is typically by surgical removal. This can be by simple excision if the cancer is small; otherwise, Mohs surgery is generally recommended. Other options include electrodesiccation and curettage, cryosurgery, topical chemotherapy, photodynamic therapy, laser surgery, or the use of imiquimod, a topical immune-activating medication. In the rare cases in which distant spread has occurred, chemotherapy or targeted therapy may be used. Basal-cell cancer accounts for at least 32% of all cancers globally. Of skin cancers other than melanoma, about 80% are BCCs. In the United States, about 35% of White males and 25% of White females are affected by BCC at some point in their lives.
Basal-cell carcinoma is named after the basal cells that form the lowest layer of the epidermis. It is thought to develop from the folliculo–sebaceous–apocrine germinative cells called trichoblasts (of note, trichoblastic carcinoma is a term sometimes used to refer to a rare type of aggressive skin cancer that may resemble a benign trichoblastoma, and can also closely resemble BCC).
Signs and symptoms Individuals with basal-cell cancer typically present with a shiny, pearly skin nodule, but superficial BCC can present as a red patch similar to eczema. Infiltrative or morpheaform BCCs can present as a skin thickening or scar tissue – making diagnosis difficult without using tactile sensation and a skin biopsy. Visually distinguishing BCC from acne scar, actinic elastosis, and recent cryodestruction inflammation is often difficult.
Cause
Most BCCs occur on sun-exposed areas of the body.
Pathophysiology
Basal-cell carcinoma (BCC) is named after the basal cells that populate the lowest layer of the epidermis due to the histological appearance of the cancer cells under the microscope. Nevertheless, not all BCCs originate within the basal layer. Some are thought to develop from the folliculo–sebaceous–apocrine germinative cells known as trichoblasts. Trichoblastic carcinoma is a term used to describe a rare and potentially aggressive malignancy that is also thought to arise from trichoblasts and may resemble a benign trichoblastoma (differential diagnosis can be challenging). It has been suggested that lesions diagnosed as trichoblastic carcinoma may actually themselves be BCC. Overexposure to the sun leads to the formation of thymine dimers, a form of DNA damage. While DNA repair removes most UV-induced damage, not all crosslinks are excised, so cumulative DNA damage can lead to mutations. Apart from the mutagenesis, overexposure to sunlight depresses the local immune system, possibly decreasing immune surveillance for new tumor cells. Studies of the role of DNA repair in susceptibility to sunlight-induced BCC indicated that reduced DNA repair capacity is one of the underlying molecular mechanisms for sunlight-induced skin carcinogenesis in the general population. Basal-cell carcinomas can often occur in association with other lesions of the skin, such as actinic keratosis, seborrheic keratosis, and squamous-cell carcinoma. In a small proportion of cases, BCC also develops as a result of basal-cell nevus syndrome, or Gorlin syndrome, which is also characterized by keratocystic odontogenic tumors of the jaw, palmar or plantar (sole of the foot) pits, calcification of the falx cerebri (in the center line of the brain), and rib abnormalities. The cause of this syndrome is a mutation in the PTCH1 tumor suppressor gene located in chromosome 9q22.3, which inhibits the hedgehog signaling pathway. A mutation in the SMO gene, which is also on the hedgehog pathway, also causes BCC.
Diagnosis
To diagnose basal-cell carcinomas, a skin biopsy is performed for histopathologic analysis. The most common method is a shave biopsy under local anesthesia. Most nodular BCCs can be diagnosed clinically; however, other variants can be challenging to distinguish from benign lesions such as intradermal naevus, sebaceomas, fibrous papules, early acne scars, and hypertrophic scarring. Exfoliative cytology methods have high sensitivity and specificity for confirming the diagnosis of BCC when clinical suspicion is high, but of unclear usefulness otherwise.
Characteristics
Basal-cell carcinoma cells resemble epidermal basal cells and are usually well differentiated. In uncertain cases, immunohistochemistry using BerEP4 can be used, having a high sensitivity and specificity in detecting only BCC cells.
Main classes Basal-cell carcinoma can broadly be divided into three groups, based on the growth patterns.
Superficial basal-cell carcinoma, formerly referred to as in-situ basal-cell carcinoma, is characterized by a superficial proliferation of neoplastic basal-cells. This tumor is generally responsive to topical chemotherapy, such as imiquimod, or fluorouracil, although surgical treatment is better able to ensure complete removal and confirm that there is not an underlying more aggressive subtype that was not sampled in the initial biopsy. Infiltrative basal-cell carcinoma, which also encompasses morpheaform and micronodular basal-cell cancer, is more difficult to treat with conservative methods, given its tendency to penetrate into deeper layers of the skin. Nodular basal-cell carcinoma includes most of the remaining categories of basal-cell cancer. It is not unusual to encounter heterogeneous morphologic features within the same tumor.
Nodular basal-cell carcinoma
… excerpt ends here. Continue reading the full article.
