الفهرس 
Basics of Basal Cell CarcinomaOnly 14 pages are availabe for public view
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Abstract
Basal cell carcinoma (BCC) is accounting approximately 75% of all skin cancers. It was first described in 1824 that is also called basal cell epithelioma, rodent ulcer or Jacobs’ ulcer.
Mortality rates with BCC are low. It may occasionally grow aggressively causing extensive tissue destruction. Metastasis is less 0.1%, but metastasis to lymph nodes, lung, bone and liver has been described.
The incidence BCC has risen dramatically in past 25 years. It increases with age and for regions closer to the equator. Only 1.8% of BCCs occur in black patients.
The major carcinogenic effect is exposure to ultraviolet ray with UV-B (280-315 nm). Exposure to UV has both direct and indirect effects. The direct effect, in DNA, it induces mutagenic photoproducts. The indirect effect is the glutathione depletion of skin cells, also invokes a degree of immunosuppression by reducing the number and the function of Langerhans cells.
Chemical carcinogens such as arsenic, coal tar products, Smoking as well as ionizing radiation and Chronic immunosuprression increases the incidence of BCC.
The source of tumor cells is the outer root sheath of hair follicles. It appears as a well-circumscribed tan-red plaque or gray papule. The tumor islands are surrounded by the characteristic palisade arrangement.
BCCs have been classified into 5 types according to their histologic characteristics and include nodular (21%), superficial (17%), micronodular (15%), infiltrative (2%) and morpheaform (1%). Many patients have a mixed pattern.
Nevoid basal cell carcinoma syndrome (Gorlin’s syndrome) is an autosomal dominant disorder. It is due to mutations of the human patched gene and the clinical manifestations include borderline intelligence, multiple skeletal abnormalities and hundreds of BCCs.
The primary prevention strategy against skin cancer consists of limiting sun exposure, especially between 10 am and 4 pm, topical application of sunscreens, extracts of the aloe plant, vitamin A, isotretinoin and Green tea may reduce the carcinogenesis of UV irradiation.
A number of treatment modalities are available and the utilization of a treatment modality depends on many factors.
Surgical excision is the most frequently used technique for treating BCC. It allows assessing the radicality of the tumor by histopathological examination. Margins for BCC excision have ranged from 2-10 mm according to size. Most patients can be treated in an ambulatory setting using local anaesthesia, but the excision margins require sacrificing unknown amounts of normal tissues.
Mohs’ micrographic surgery (MMS) is the gold standard for excising primary BCC. The technique results in extremely high cure rates for even the most high- risk lesions together with maximal preservation of normal tissues, but it is time consuming, labor intensive and more expensive than other modalities.
Curettage and cautery (C&C) is generally suitable for the treatment of low risk lesions (small nodular or superficial BCC). Removal of high risk facial lesions by C&C is generally contraindicated. The technique is inexpensive, time-efficient and simple surgical procedure.
Cryosurgical technique using the extreme cold liquid nitrogen to cause necrosis of the tumor and surrounding tissues. Advantages include simple use, minimal bleeding, low costs, but it is a blind technique with permanent complications and it is contraindicated in the H-zone, hairy scalp, eyebrows, lower legs and feet.
Radiotherapy is effective as adjuvant therapy and is probably the treatment of choice for high risk lesions in patients who are unable to tolerate surgery. It is painless, but it is more expensive, very time consuming and the cosmetic outcome declines after treatment. Radiation therapy is contraindicated in certain genetic disorders such as Gorlin’s syndrome, where it may promote the growth of new BCCs.
The topical therapeutic agent most widely used for Cutanous tumors is 5-fluorouracil (5-FU). It is a chemical ablative agent that inhibits DNA synthesis, prevents cell proliferation. Imiquimod (IMQ) is a topical immune response modulator. The mechanism of action occurs through the activation of immune cells. It also promotes the secretion of cytokines which cause the antitumor effects.
Interferons (IFN) initiates apoptosis of BCC cells via the stimulation of interleukins. IFN-α has been shown to have activity against a variety of tumors. Treatment with IFN can cause flu-like symptoms, has a low cure rate and need for multiple injections.
Photodynamic therapy (PDT) is a nonionizing radiation treatment modality. The main principle of PDT is use of the interaction between visible light and a photosensitizer to cause cell death.
The introduction of topical PS, porphyrin precursor 5-aminolevulinic acid (ALA) and later methyl aminolevulinic acid, both, were significant milestones in the development of PDT. The 5-ALA is a prodrug which is enzymatically converted to Protoporphyrin IX and accumulates in the tumor cells.
On activation of a PS with light, it can absorb photons and become excited. Energy from the excited PS is transferred to the O2 to give singlet oxygen (1O2) and other reactive oxygen species. These cytotoxic photoproducts induce apoptosis of neoplastic cells.
The ideal light source in cutaneous PDT should be well absorbed by the photosensitizer, delivers the light energy in less time and with greater selectivity for the target. Recently, light emitting diodes are more than satisfactory for cutaneous use.
In multiple studies, topical PDT has demonstrated efficacy in the treatment of BCC. Clearance rates for BCC range from 76-97% for superficial tumors and 64-92% for nodular BCCs.
An important indication for PDT is Gorlin’s syndrome, in which the multiple tumors can be clinically and cosmetically controlled in an effective and minimally morbid way. Morphoeic BCC and pigmented tumors appear to respond poorly to PDT and are best avoided.
PDT is noninvasive, repeatable and applicable. It is well tolerated and gives excellent cosmetic results and adverse events such as, burning sensation during illumination may occur.
The use of PDT seems promising especially for management of superficial BCCs. Larger studies are needed to confirm the efficacy of this method and its benefits in patients with NBCS.
Laser systems are electro-optical devices that convert electricity into intense beam of pure colored light. All laser systems are composed of active medium, the resonator, the power supply and a delivery system.
Laser light is monochromatic, coherent and collimated. When laser light strikes the skin, it can be reflected or absorbed at each layer of the skin. Only the absorbed light produces tissue effects. Absorbed light energy can produce thermal, chemical and mechanical effects on the skin.
Laser may be used as light source in PDT, or used as surgical ablative method for superficial lesions of the skin. The CO2 laser is known as laser scalpel produces light in infrared spectrum at 10,600 nm. It utilizes water as the main chromophore, causing heating and vaporization of cellular water resulting in tissue destruction.
In the continuous mode laser, the induced heat diffuses into the surrounding tissues, leading to nonspecific damage. In the pulsed mode, the pulse duration must be shorter than the TRT to minimize nonspecific lateral thermal damage.
The erbium: yttrium aluminum garnet emits light at a wavelength of 2940 nm. Because the wavelength approximates the absorption peak of water, nearly all the energy is absorbed in the epidermis. This thinner zone of ablation resulting in lower rate of post procedure side effects compared with CO2 lasers.
Advantages of ablative laser include, bloodless field, decreased postoperative pain and it can be used in infected surgical sites, CO2 laser limiting the transfer of infected or malignant cells and sterilizes the treated area and is suitable for nonsurgical patients or patients with multiple tumors.
Other type of laser as the pulsed dye laser (595 nm) was used to treat superficial BCCs. It results in Photoangiolysis of sublesion microcirculation with denaturation of the basement membrane and cellular destruction.
Laser safety is the first principle in laser therapy. Using laser technologies, requiring considerable knowledge of the exact treatment parameters of each lesion and guidelines for safety, to achieve the best results with minimal side effects.
Laser therapy offers some advantages in selected patients, but when treating invasive tumors one has to bear in mind the lack of histologic control.
For the Food and Drug Administration to approve a laser, it must go through a series of rigorous clinical trials on animals and humans.