The skin is the largest organ of the human body, serving in both a protective and aesthetic capacity. Skin cancer refers to several types of malignancies that can occur, including basal cell carcinoma (BCC), squamous cell carcinoma (SCC), and malignant melanoma. While the first two types of skin malignancies are usually more amenable to treatment and are often described together as nonmelanoma skin cancers (NMSC), melanoma is classified as a separate type of cancer with typically more aggressive behavior and worse prognosis.
The incidence of skin cancers as a group is on the rise and currently accounts for over one-third of all diagnosed malignancies worldwide and nearly 45% of malignancies in the United States. In fact, the incidence of melanoma over the past fifty years has increased at a higher rate than with almost any other cancer. This increase in incidence is thought to be largely related to increases in lifetime cumulative sun-exposure and more intense diagnostic scrutiny, indicating the tremendous importance of preventative programs and early detection strategies to reduce the incidence and mortality of skin cancers. Please visit the University of Pennsylvania's OncoLink skin cancer section for general information and relevant National Cancer Institute literature.
Epidemiology and Etiology
- Incidence of more than 1 million new cases of NMSCs annually in the United States alone; The incidence of melanoma in the United States is nearly 60,000 new cases annually, with rates 15-20 times higher in whites than in blacks or Asians. Melanoma is the fifth most common cancer among American males and the sixth most common among females. Incidence is approximately 30% higher among men than women. Overall, 75-80% of newly diagnosed skin cancers are basal cell carcinomas, 15-20% are squamous cell carcinomas, 4-6% are invasive melanomas, and approximately 1% are such rare skin cancers as Kaposi's sarcoma, dermatofibrosarcoma protuberans, cutaneous T cell lymphoma, Merkel cell carcinoma, and microcystic adnexal carcinoma.
- Mortality from BCC and SCC of approximately 2,820 people annually in the United States, while melanoma results in about 7,770 deaths each year. Nearly two-thirds of all deaths attributed to melanoma occur in males [1, 2].
- Etiology is multifactorial and dependent on both constitutional/genetic factors (fair skin color, propensity to burn from sun exposure, tendency to freckle, red or blonde hair) as well as environmental factors (sun exposure).
- Hereditary factors include several familial melanoma or dysplastic nevi syndromes, a family history of malignant melanoma, and xeroderma pigmentosum (XP ), a rare congenital genetic defect in repair of ultraviolet radiation-induced DNA damage. Patients with skin cancers associated with such hereditary factors often present at an earlier age of onset.
- Risk factors associated with the development of NMSC and malignant melanoma (MM) include the following [3, 4]:
- Exposure to ultraviolet radiation, particularly UV-B radiation from sunlight
- While BCC and SCC usually occur on chronically exposed areas of skin, MM, with the exception of the lentigo maligna melanoma subtype, is usually more dependent on intermittent sun exposure that results in blistering sunburns, especially during childhood
- Light skin, hair, or eye coloring
- Personal history of previous BCC, SCC, and/or MM lesions
- Family history of skin cancer in a first-degree relative
- Increasing age
- Male gender
- Geographically living at lower latitudes, closer to the equator
- Northern European ancestry
- Immunosuppression or a history of prior hematologic malignancy
- Occupational or environmental exposures to radium, arsenic, tar, creosote, or pitch
- History of previous superficial therapeutic radiation
- Greater than 25 melanocytic nevi (benign moles) or ?1 atypical or dysplastic nevus increase the risk of developing MM
- Presence of lesions called actinic keratoses (erythematous and scaly skin patches that usually result from chronic sun exposure) increase the risk of developing SSC
- History of current or previous smoking increases the risk of developing SCC and, possibly, BCC
- The American Cancer Society recommends the following :
- Avoid direct sun exposure between 10am and 4pm, since the ultraviolet rays from the sun are most intense during this time.
- Avoid sun lamps and tanning beds, which are artificial sources of ultraviolet radiation.
- Cover all sun-exposed skin with sunscreen lotion that has a sun protection factor (SPF) of at least 15.
- Wear clothing that covers as much as possible of the arms, legs, and torso.
- Wear hats with wide brims to shade the face, neck, eyes, and ears.
- The American Academy of Dermatologists and the Centers for Disease Control and Prevention recommend regular skin self-examinations and focused evaluations of all suspicious skin lesions by primary care providers or dermatologists. High-risk patients may benefit from annual physician total skin examinations.
- Given the high prevalence of NMSCs, routine total skin examinations and skin self-examinations could detect more malignancies than cancer screenings for any other organ.
- The effectiveness of skin cancer screening programs is examiner-dependent, as skin cancer specialists and dermatologists receive much better training than primary care physicians in the diagnosis of skin malignancies. In fact, screening examinations conducted by dermatologists have a ?80% sensitivity and ?90% specificity for melanoma detection [6, 7].
- Two common screening checklists include the American Cancer Society's ABCDE system ( A symmetry, B order irregularity, C olor variegation, D iameter >6 mm, E nlargement/ E volutionary change) and the Glasgow seven-point checklist .
- History: NMSCs often present as a nonhealing sore, or ulcer, papule, or plaque. MMs usually present as either a new nevus or a change in the appearance of a preexisting mole or nevus.
- Physical exam:BCC = small, firm, well-demarcated, dome-shaped papule, ranging from pearly white to pink or red, with central ulceration and raised borders; SCC = hyperkeratotic raised, firm papule, nodule, or plaque; BCC or SCC = scaling red/pink patch, enlarging pink papule or nodule, or a new nodule with scaling, erosion, ulceration, or crusting; MM = new or old nevus that has irregular borders, dark or multiple pigmentations , or appears asymmetrical, elevated, eroded, crusted, or ulcerated. Upon the identification of any type of potentially malignant skin lesion, a total-body skin examination and lymph node evaluation should be conducted.
- Lab studies: no characteristic findings unless metastatic disease is present.
- Radiologic studies: depending on the type and size of the malignant lesion, a chest x-ray with CT scans, bone scans, PET scans, and MRIs may be warranted for metastatic workup.
- Diagnostic studies: biopsy is absolutely essential for diagnosis. Depending on the type and size of the lesions, biopsy techniques may include punch, shave, saucerization, and elliptical incision or excision biopsies. While punch or incisional biopsies are often used for large lesions or lesions in cosmetically sensitive locations, a complete excisional biopsy is typically preferred for smaller lesions.
Natural Course and Pathology
- Basal cell carcinoma: malignant transformation of basal cells.
- Universally contains both epidermal and dermal components with no keratinization.
- Common sites of primary BCCs: face (65-70%), nose (25-30%), trunk (15%) .
- Histopathologic subtypes
- Nodular : 60-65% of all BCCs; usually presents on the face as a flesh-colored or pink papule with a pearly appearance and a telangiectatic vessel in the papule, with or without ulceration.
- Superficial : 25-30% of BCCs; more common in men than women; usually presents on the trunk as a light red scaly plaque or papule.
- Morpheaform (sclerosing) : 5-10% of BCCs; usually presents as smooth, flesh-colored atrophic and firm papules or plaques, often with ill-defined borders; highest rate of recurrence of BCCs.
- Staging: clinical staging is completed through the inspection and palpation of lesions and involved lymph nodes; pathological staging is established by the examination of the resected specimen.
- Prognosis: although tumors are typically slow-growing and nonmetastatic in nature, lesions can become bulky and invade locally.
- The rate of metastasis is ?0.1% and is usually seen in patients with deeply invasive or large lesions. Metastatic lesions have one- and five-year actuarial survival probabilities under 20% and 10%, respectively. Overall, the mortality rate from BCC is between 0.02% and 0.05%. Morbidity and disfigurement from local invasion of these tumors may be significant [10, 11].
- Second primary malignancies: following a diagnosis of BCC, the 3-year cumulative risk of developing a second BCC lesion is ~44%. Additionally, there is about a 6% risk of developing SCC, a two- to four-fold increased risk of developing melanoma, and a one-and-a-half- to three-fold increased risk of developing noncutaneous malignancies [12, 13, 14, 15].
- Squamous cell carcinoma: malignant transformation of keratinocytes.
- SCCs originate in the epidermis and may occur anywhere on the skin or mucus membranes where squamous epithelium is present.
- Malignant SCC lesions may arise from actinic keratosis or Bowen's disease, which is commonly considered SCC in situ and usually presents as a red or pink epidermal plaque with variable hyperkeratosis.
- Lesions can rapidly progress to epidermal filling, dermal invasion, and local tissue infiltration and destruction.
- Staging: is the same as for BCC.
- Prognosis: is worse for larger tumors, deeper lesions, recurrent tumors, lesions with ill-defined borders, and tumors originating on the dorsa of the hands or head and neck, especially near critical structures or cosmetically-sensitive areas.
- Metastatic potential is largely dependent on tumor location, depth, and size. The rate of metastasis is ?5%. Overall, the five-year survival for patients with cutaneous SCCs is ?90% .
- Second primary malignancies: following a diagnosis of SCC, the 3-year cumulative risk of developing a second SCC lesion is ~18%. Additionally, there is about a 40% risk of developing BCC, and a one-and-a-half- to three-fold increased risk of developing noncutaneous malignancies [12, 14].
- Malignant melanoma: malignant transformation of melanocytes.
- Primary MM lesions usually appear cutaneously, but lesions can also present in the eye, anus and GI tract, meninges, ear, and oral or genital mucous membranes.
- While the majority of cases occur in patients younger than age 70, the mean age at diagnosis is 55 years .
- Approximately 10% of cases are familial, and these patients typically present at younger ages.
- Disease at presentation: 85% of patients with clinically localized disease, 11% with regional involvement, and 4% with metastatic disease [1, 16].
- Two growth phases: radial, which features outward (lateral) expansion and lasts for a variable period of time, and vertical, which usually follows a period of radial growth and features rapid cellular invasion through the dermis.
- Radial growth phase cells typically do not metastasize, but vertical phase cells have a greater metastatic potential since they can access dermal lymphatics and blood vessels.
- Histopathologic subtypes
- Superficial spreading : 65-75% of all MMs; usually presents as a deeply pigmented macule, plaque, or nevus that grows radially prior to vertical invasion.
- Nodular : 15-30% of MMs; often presents as a darkly pigmented discrete nodule with initial vertical growth without a radial growth phase.
- Lentigo maligna : 5-10% of MMs; usually arises from in situ melanoma and occurs on the head and neck.
- Acral lentiginous : 2-7% of MMs; most common subtype found in dark-skinned patients; usually presents on the palms, soles and nail beds, and is associated with a poorer prognosis.
- Staging: the American Joint Committee on Cancer TNM staging incorporates two systems: Clark 's levels (I through V) describe the depth of tumor invasion qualitatively, via description of the skin layer into which it invades, and Breslow's thicknesses describe the depth of invasion quantitatively, in millimeters. While both systems correlate with prognosis, Breslow's thickness is better able to predict survival.
- Prognosis is worse in patients with: lesions on the trunk, back, and head and neck; positive lymph nodes or angiolymphatic invasion; acral lentiginous lesions; tumors with high mitotic rates; ulcerated lesions; and in patients over age 65. Stage, nodal involvement, and tumor thickness are the most important predictors of survival [3, 17].
- Metastatic potential is directly correlated with tumor thickness. Metastasis typically progresses from local disease or recurrence to regional metastasis to distant spread .
- Five-year survival rates are 98% for patients with localized disease, 60% for regionally advanced disease, and 16% for metastatic disease. Overall, the 5-year survival rate for all patients diagnosed with cutaneous melanoma is 91%, improved from 81% thirty years ago [1, 16].
- Second primary malignancies: following a diagnosis of MM, there is a >10-fold increased risk of developing a second MM lesion. Additionally, there is a three- to four-fold increased risk of developing a NMSC, and a one- to two-fold increased risk of developing noncutaneous malignancies [18, 19].
- Basal cell and Squamous cell carcinomas
- Complete surgical excision and Mohs micrographic surgery are the mainstays of therapy for NMSCs. While standard surgical excision can achieve cure rates of ?90%, Mohs surgery can be used for select lesions to better achieve tumor-free margins and produce a 95-99% cure rate.
- Mohs surgery with intraoperative frozen section margin evaluation is preferred over standard surgical excision for NMSCs >2 cm, lesions with poorly-defined borders, or high-risk lesions [20, 21, 22, 23].
- Laser surgery,curettage and electrodessication,and cryosurgery result in less controlled treatment margins, but are rapid and cost-effective therapeutic modalities that may be used to treat superficial and small NMSCs, particularly BCCs.
- Radiation therapy is the treatment of choice for select small lesions in locations that would be difficult to excise, such as the eyelid, ear pinna, nasolabial fold, and lips. These lesions have 90-95% cure rates.
- Chemotherapy , such as topical and intralesional fluorouracil , is useful for treating small, superficial BCC's.
- Retinoids are used in both the prevention and treatment of skin cancers, causing cancer regression in some cases by an unknown mechanism of action.
- Photodynamic therapy (PDT), which combines a photosensitizing drug with a specific type of light to kill localized cancer cells, can effectively treat actinic keratoses and superficial NMSCs .
- Malignant melanoma
- Surgical excision with disease-free margins can result in long-term survival for patients with solitary or limited lesions.
- Current surgical margin recommendations: 1 cm margin of normal tissue for lesions <1 mm in thickness, 2 cm margin for lesions 1-4 mm in thickness, and ?2 cm margin for lesions >4 mm in thickness .
- Lymph node dissection is controversial, as removal would eliminate the most likely source of metastasis, but 80-85% of patients with stage I and II disease have negative lymph nodes at the time of surgery [3, 25].
- For patients with clinically positive or enlarged lymph nodes, a fine needle aspiration (FNA) should be performed. A complete lymphadenectomy should be conducted in patients with a positive tissue sample for metastasis.
- For patients with clinically negative nodes, a sentinel lymph node biopsy is generally performed in patients with poor prognostic factors, MMs that are deeper than 1 mm, or lesions that invade to Clark's level IV or greater.
- Chemotherapy with dacarbazine (DTIC-Dome), temozolomide (Temodar), cisplatin (Platinol-AQ), or combination regimens can achieve response rates ranging from 10%-62% in patients with advanced disease [3, 26, 27].
- Radiation therapy may be the primary treatment of choice for select patients who are not surgical candidates, either because of the size or location of the lesion or other physical limitations. Radiation should also be considered postoperatively for patients who are at high risk of regional recurrence who have gross extracapsular extension or multiple involved lymph nodes.
- Immunotherapy is an area of much research, with the two most promising applications being the treatment of metastatic disease and the adjuvant (postoperative) treatment of high-risk patients.
- Nonspecific agents such as interferon-alpha, interleukin-2 (IL-2), and Bacille Calmette-Guerin (BCG) serve to stimulate the immune system as a whole. Specific agents such as monoclonal antibodies and melanoma vaccines more specifically target tumor cells.
- In patients with high-risk resected stage IIB and III melanoma, adjuvant interferon-alpha 2b has been shown to improved relapse-free survival but not significantly improve overall survival .
- In patients with advanced melanoma, high-dose regimens of IL-2 have achieved objective response rates of 20%, with half of these patients attaining complete remissions lasting >5 years .
- Hormonal therapy with tamoxifen (Nolvadex), as part of a multidrug regimen, has been shown to give response rates of up to 50%. Although the mechanism of action of tamoxifen in the treatment of melanoma is not completely understood, estrogen receptors have been found on melanoma tumors, and these tumors are thought to be estrogen-dependent [27, 29].
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