Chapter 44 Common cutaneous malignancies
1. How are skin cancers classified?
Primary cutaneous cancers are classified on the basis of their cell of origin within the skin (Table 44-1). Skin cancers are most commonly derived from keratinocytes (e.g., squamous cell carcinoma) or melanocytes (e.g., malignant melanoma), which are normal components of the epidermis. Less commonly, they arise from other cells within the epidermis, dermis, or subcutis.
2. What are the most common nonmelanoma skin cancers (NMSCs)?
Basal cell carcinoma and squamous cell carcinoma. In the United States, over 1 million cases of NMSCs occur yearly, which makes these the most prevalent of all malignancies. Common nonmelanoma skin premalignancies include actinic keratosis, actinic cheilitis, and squamous cell carcinoma in situ (Bowen’s disease).
Table 44-1. Classification of Cutaneous Malignancies
| MALIGNANCY | CELL OF ORIGIN |
|---|---|
| Premalignancies (in situ) | |
| Actinic keratosis | Keratinocyte |
| Squamous cell carcinoma in situ (Bowen’s disease) | Keratinocyte |
| Malignant melanoma in situ | Melanocyte |
| Lentigo maligna (Hutchinson’s freckle) | Melanocyte |
| Common Cutaneous Malignancies | |
| Basal cell carcinoma | Follicular keratinocyte origin (probable) |
| Squamous cell carcinoma | Epidermal keratinocyte |
| Keratoacanthoma | Follicular keratinocyte |
| Melanomas | |
| Malignant melanoma | Melanocyte |
| Lentigo maligna melanoma | Melanocyte |
| Uncommon Cutaneous Epithelial Malignancies | |
| Sweat gland carcinoma (numerous variants) | Apocrine or eccrine sweat gland/duct |
| Follicular carcinomas (several variants) | Follicular epithelial cells |
| Extramammary Paget’s disease | Modified keratinocytes (Toker cell) |
| Merkel cell carcinoma | Neuroendocrine cell |
| Cutaneous Mesenchymal Malignancies | |
| Atypical fibroxanthoma | Fibroblast |
| Dermatofibrosarcoma protuberans | CD34+ dermal dendrocyte |
| Fibrosarcoma | Fibroblast |
| Angiosarcoma | Endothelial cell |
| Kaposi’s sarcoma | Endothelial cell |
| Hemangiopericytoma | Pericyte |
| Malignant peripheral nerve sheath tumors | Schwann cells |
| Liposarcoma | Lipocyte |
Diepgen TL, Mahler V: The epidemiology of skin cancer, Br J Dermatol 146:1–6, 2002.
Nguyen TH, Ho DQ: Nonmelanoma skin cancer, Curr Treat Options Oncol 3:193–203, 2002.
3. What is the most important cause of NMSC?
The overwhelming majority of precancerous and cancerous skin lesions are caused by sun exposure. Several observations and epidemiologic studies support the role of ultraviolet light in the production of skin cancers:
1. Most NMSCs develop on skin chronically exposed to the sun, with 85% or more occurring on the head and neck.
2. The incidence of NMSC is lower in more polar latitudes (e.g., Minneapolis) than equatorial latitudes (e.g., Hawaii).
3. Epidemiologic studies clearly demonstrate that NMSCs are much more common in individuals with lighter skin than in individuals with darker skin.
5. What special populations are at increased risk of NMSC?
• Organ transplant patients: NMSC is the most common malignancy in solid organ transplant recipients. Increased rates of NMSC are seen on average 8 to 10 years after transplantation, and the development of skin cancer in these patients appears to be linked to the duration and degree of immunosuppression required to prevent transplant rejection. The ratio of squamous cell carcinomas (SCCs) to basal cell carcinomas (BCCs) is higher in transplant patients, a reversal of the normal ratio seen in the general population.
• Human immunodeficiency virus (HIV) patients: NMSC is the most common nonacquired immune deficiency syndrome (AIDS)–defining cancer seen in HIV-positive patients. HIV-positive patients appear to maintain a normal ratio of BCCs to SCCs, but are two- to sevenfold more likely to develop NMSC than the general population.
Honda K: HIV and skin cancer, Dermatol Clin 24:521–530, 2006.
6. How are NMSCs diagnosed?
A cutaneous malignancy should always be considered in any patient who reports a new lesion on the skin, particularly in sun-exposed skin. Currently, the diagnosis is established by shave, punch, incisional, or excisional biopsy, with the choice of biopsy technique depending on the size and location of the suspected malignancy. Current research is focused on developing non-invasive methods of diagnosing NMSC by using techniques such as specialized types of ultrasonography and microscopy. However, these methods are currently in development and have not replaced skin biopsy with histologic examination as the gold standard for diagnosis.
7. How frequently do NMSCs occur?
The exact incidence of NMSCs is unknown, because they are not routinely entered into tumor registries. It is estimated that 1.3 million new cases of NMSC occur each year in the United States, making them by far the most common cancers in this country. The annual cost to Medicare for the management and treatment of NMSCs is 426 million dollars. The lifetime risk of developing NMSC is 1 in 5. Statistically, if a patient develops one NMSC, the risk of another new lesion in 5 years is 30% to 50%.
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