Instruct: Given a question, retrieve documents that can help answer the question.
Query: What percentage of people will get basal-cell carcinoma?
Basal-cell cancer accounts for at least 32% of all cancers globally.[7][11] Of skin cancers other than melanoma, about 80% are basal-cell cancers.[2] In the United States, about 35% of white males and 25% of white females are affected by BCC at some point in their lives.[2]
About two thirds of basal-cell carcinomas occur on sun-exposed areas of the body. One-third occur on areas of the body that are not exposed to sunlight, emphasizing the genetic susceptibility of basal-cell cancer.
Basal-cell carcinoma (BCC), also known as basal-cell cancer, is the most common type of skin cancer.[2] It often appears as a painless raised area of skin, which may be shiny with small blood vessels running over it; or it may present as a raised area with ulceration.[1] Basal-cell cancer grows slowly and can damage the tissue around it but is unlikely to spread to distant areas or to result in death.[7]
Patients with ocular sebaceous carcinomas present with nonhealing eyelid tumors that are often misdiagnosed for more common benign conditions such as chalazion or bleproconjunctivitis. Extraocular SGc appears similarly to skin cancers such as basal cell carcinoma, squamous cell carcinoma and benign lesions such a molluscum contagiosum and pyogenic granuloma. Many tumors also share a histological presentation similar to SGC, such as sebaceous adenomas, basal cell carcinomas (BCC), squamous cell carcinomas (SCC) and clear cell tumors. A high level of suspicion is extremely important to prevent treatment delay and increased mortality.
To diagnose basal-cell carcinomas, a skin biopsy is performed for histopathologic analyses. The most common method is a shave biopsy under local anesthesia. Most nodular basal-cell cancers can be diagnosed clinically; however, other variants can be very difficult to distinguish from benign lesions such as intradermal naevus, sebaceomas, fibrous papules, early acne scars, and hypertrophic scarring.[16]
Possible associations with cervical carcinoma, cutaneous squamous cell carcinoma, Bowen's disease, basal cell skin carcinoma, extrapulmonary small cell carcinoma, and EGFR mutation-driven non-small cell lung cancer have been reported.
Approved in 2012, vismodegib is used to treat an advanced form of basal-cell carcinoma.[51]
Basaloid squamous cell carcinoma (Bas-SqCC) is an uncommon histological variant of lung cancer composed of cells exhibiting cytological and tissue architectural features of both squamous cell lung carcinoma and basal cell carcinoma.
There are three main types of skin cancer: basal-cell skin cancer (basal-cell carcinoma) (BCC), squamous-cell skin cancer (squamous-cell carcinoma) (SCC) and malignant melanoma.
Most sporadic BCC arises in small numbers on sun-exposed skin of people over age 50, although younger people may also be affected. The development of multiple basal-cell cancer at an early age could be indicative of nevoid basal-cell carcinoma syndrome, also known as Gorlin's Syndrome.[58]
Nevoid basal-cell carcinoma syndrome (NBCCS), also known as basal-cell nevus syndrome, multiple basal-cell carcinoma syndrome, Gorlin syndrome, and Gorlin–Goltz syndrome, is an inherited medical condition involving defects within multiple body systems such as the skin, nervous system, eyes, endocrine system, and bones. People with this syndrome are particularly prone to developing a common and usually non-life-threatening form of non-melanoma skin cancer. About 10% of people with the condition do not develop basal-cell carcinomas (BCCs). 
Basal-cell cancer is a very common skin cancer. It is much more common in fair-skinned individuals with a family history of basal-cell cancer and increases in incidence closer to the equator or at higher altitude. There are approximately 800,000[55] new cases yearly in the United States alone. Up to 30% of Caucasians develop basal-cell carcinomas in their lifetime.[56] In Canada, the most common skin cancer is basal-cell carcinoma (as much as one third of all cancer diagnoses), affecting 1 in 7 individuals over a lifetime.[57]
Basal-cell carcinomas are currently considered to have origin from the folliculo-sebaceous-apocrine germ, also known as trichoblast. The differential diagnosis with trichoblastic carcinoma, a rare malignant form of trichoblastoma, can be challenging.[12] Alternatively, one argument is that basal-cell carcinoma is trichoblastic carcinoma.[13] Overexposure to 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. There is, therefore, cumulative DNA damage leading to mutations. Apart from the mutagenesis, overexposure to sunlight depresses the local immune system, possibly decreasing immune surveillance for new tumor cells.
Cystic basal-cell carcinoma Micronodular basal-cell carcinoma Superficial basal-cell carcinoma Micrograph of a fibroepithelioma of Pinkus
Basal-cell carcinoma can be divided into three groups, based on the growth patterns.
Basal-cell carcinoma is a common skin cancer and occurs mainly in fair-skinned patients with a family history of this cancer. Sunlight is a factor in about two-thirds of these cancers; therefore, doctors recommend sunscreens with at least SPF 30. However, a Cochrane review examining the effect of solar protection (sunscreen only) in preventing the development of basal-cell carcinoma or cutaneous squamous cell carcinoma found that there was insufficient evidence to demonstrate whether sunscreen was effective for the prevention of either of these keratinocyte-derived cancers.[19] The review did ultimately state that the certainty of these results were low, so future evidence could very well alter this conclusion. One-third occur in non-sun-exposed areas; thus, the pathogenesis is more complex than UV exposure as the cause.
Nevoid basal-cell carcinoma syndrome
Some superficial cancers respond to local therapy with 5-fluorouracil, a chemotherapy agent. Topical treatment with 5% Imiquimod cream, with five applications per week for six weeks has a reported 70–90% success rate at reducing, even removing, the BCC [basal-cell carcinoma]. Both Imiquimod and 5-fluorouracil have received FDA approval, and topical IMQ is approved by the European Medicines Agency for treatment of small superficial basal-cell carcinoma.[45] Off label use of imiquimod on invasive basal-cell carcinoma has been reported. Imiquimod may be used prior to surgery in order to reduce the size of the carcinoma. One can expect a great deal of inflammation with this treatment.[49] Chemotherapy often follows Mohs surgery to eliminate the residual superficial basal-cell carcinoma after the invasive portion is removed. Some advocate the use of imiquimod prior to Mohs surgery to remove the superficial component of the cancer.[50] Removing the residual superficial tumor with surgery alone can result in large and difficult to repair surgical defects. One often waits a month or more after surgery before starting the Imiquimod or 5-fluorouracil to make sure the surgical wound has adequately healed. Some people advocate the use of curettage (see EDC below) first, followed by chemotherapy. These experimental procedures are not standard care. The 2008 study reported that topical IMQ appears effective in the treatment of primary small superficial BCCs but only "may possibly" have a role in the treatment of primary nodular BCC.[45]
Basal-cell carcinomas can often come in association with other lesions of the skin, such as actinic keratosis, seborrheic keratosis, squamous cell carcinoma.[14] In a small proportion of cases, basal-cell carcinoma 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 basal-cell carcinoma.[15]
Nevoid basal cell carcinoma syndrome (NBCCS), also known as Gorlin syndrome, is an autosomal dominant cancer syndrome in which the risk of basal cell carcinoma is very high. The disease is characterized by basal cell nevi, jaw keratocysts and skeletal abnormalities. Estimates of NBCCS prevalence varies, but is approximately 1 in 60000. The presence of basal cell carcinoma is much higher in white than black individuals; 80% and 38%, respectively. Odontogenic keratocysts are found in approximately 75% of individuals with the disease and often occur early in life. The most common skeletal abnormalities occur in the head and face, but other areas are often affected such as the rib cage. The causative genetic mutation of this disease occurs in the PTCH gene, and the product of PTCH is a tumor suppressor involved in cell signaling. Although the exact role of this protein in NBCCS is not known, it is involved in the hedgehog signaling pathway, known to control cell growth and development.[29][30]
Superficial basal-cell carcinoma, formerly referred to in-situ basal-cell carcinoma, is characterized by a superficial proliferation of neoplastic basal-cells. This tumor is generally responsive to topic chemotherapy, such as imiquimod, or fluorouracil. 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 (also known as "classic basal-cell carcinoma") most commonly occurs on the sun-exposed areas of the head and neck.[17]:748[18]:646 Cystic basal-cell carcinoma is morphologically characterized by dome-shaped, blue-gray cystic nodules.[18]:647 Cicatricial basal-cell carcinoma (also known as "morpheaform basal-cell carcinoma," and "morphoeic basal-cell carcinoma") is an aggressive variant with a distinct clinical and histologic appearance.[17]:748[18]:647 Infiltrative basal-cell carcinoma is an aggressive type characterized by deep infiltration.[18]:647 Micronodular basal-cell carcinoma is characterized by a micronodular growth pattern.[18]:647 Superficial basal-cell carcinoma (also known as "superficial multicentric basal-cell carcinoma") occurs most commonly on the trunk and appears as an erythematous patch.[17]:748[18]:647 Pigmented basal-cell carcinoma exhibits increased melanization.[17]:748[18]:647 About 80% of all basal-cell carcinoma in Chinese are pigmented while this subtype is uncommon in white people. Rodent ulcer (also known as a "Jacob's ulcer") is a large skin lesion of nodular basal-cell carcinoma with central necrosis.[17]:748[18]:647 Fibroepithelioma of Pinkus most commonly occurs on the lower back.[17]:748[18]:648 Polypoid basal-cell carcinoma is characterized by exophytic nodules (polyp-like structures) on the head and neck.[18]:648 Pore-like basal-cell carcinoma resembles an enlarged pore or stellate pit.[18]:648 Aberrant basal-cell carcinoma is characterized by the formation of basal-cell carcinoma in the absence of any apparent carcinogenic factor, occurring in odd sites such as the scrotum, vulva, perineum, nipple, and axilla.[18]:648
Dermoscopy showing telangiectatic vessels Basal-cell carcinoma
In the United States approximately 3 out of 10 caucasians develop a basal-cell carcinoma during their lifetime.[56] This tumor accounts for approximately 70% of non-melanoma skin cancers. In 80 percent of all cases, basal-cell carcinoma affects the skin of head and neck.[56] Furthermore, there appears to be an increase in the incidence of basal-cell cancer of the trunk in recent years.[56]
Alterations in this gene have been associated with nevoid basal cell carcinoma syndrome, basal cell carcinoma, medulloblastoma, and susceptibility to congenital macrostomia.