Chapter 083. Cancer of the Skin (Part 9) Squamous Cell Carcinoma The natural history of SCC depends on both tumor and host characteristics. Tumors arising on actinically damaged skin have a lower metastatic potential than those on protected surfaces. The metastatic frequency of cutaneous SCC, reported at 0.3–5.2%, occurs most frequently in regional draining lymph nodes. Tumors occurring on the lower lip and ear have metastatic potentials approaching 13 and 11%, respectively. The metastatic potential of SCC arising in scars, chronic ulcerations, and genital or mucosal surfaces is higher. The overall metastatic rate for recurrent tumors may approach 30%. Large, poorly differentiated, deep tumors, with perineural or lymphatic invasion, often behave aggressively. Multiple tumors with rapid growth and aggressive behavior can be a therapeutic challenge in immunosuppressed patients. Nonmelanoma Skin Cancer: Treatment Basal Cell Carcinoma The most frequently employed treatment modalities for BCC include electrodesiccation and curettage (ED&C), excision, cryosurgery, radiation therapy, laser therapy, Mohs micrographic surgery (MMS), topical 5-fluorouracil, and topical immunomodulators. The mode of therapy chosen depends on tumor characteristics, patient age, medical status, preferences of the patient, and other factors. ED&C remains the method most commonly employed by dermatologists. This method is selected for low-risk tumors (e.g., a small primary tumor of a less aggressive subtype in a favorable location). Excision, which offers the advantage of histologic control, is usually selected for more aggressive tumors or those in high-risk locations or, in many instances, for aesthetic reasons. Cryosurgery employing liquid nitrogen may be used for certain low-risk tumors but requires specialized equipment (cryoprobes) to be effective for advanced neoplasms. Radiation therapy, while not used as often, offers an excellent chance for cure in many cases of BCC. It is useful in patients not considered surgical candidates and as a surgical adjunct in high-risk tumors. Younger patients may not be good candidates for radiation therapy because of the risks of long-term carcinogenesis and radiodermatitis. Despite rapidly advancing technology in laser development, their long-term efficacy in treating infiltrative or recurrent lesions is still unknown. On the other hand, MMS, a specialized type of surgical excision that permits the best histologic control and preservation of uninvolved tissue, is associated with cure rates >98%. It is the preferred modality for lesions that are recurrent, in a high-risk location, or large and ill-defined and where maximal tissue conservation is critical (e.g., the eyelids). Topical 5-fluorouracil therapy should be limited to superficial BCC. New topicals, the immunomodulators, show promise in their efficacy at treating superficial and even nodular BCCs. Imiquimod, a relatively well-tolerated cream, has successfully undergone phase III clinical trials. Intralesional chemotherapy (5-fluorouracil and INF) and photodynamic therapy (which employs selective activation of a photoactive drug by visible light) have been used successfully in patients with numerous tumors. A topical endonuclease (T4N5 liposome lotion) has been shown to repair DNA and may decrease the rate of NMSC in xeroderma pigmentosum. Squamous Cell Carcinoma The therapy of cutaneous SCC should be based on an analysis of risk factors influencing the biologic behavior of the tumor. These include the size, location, and degree of histologic differentiation of the tumor as well as the age and physical condition of the patient. Surgical excision, MMS, and radiation therapy are standard methods of treatment. Cryosurgery and ED&C have been used successfully for premalignant lesions and small primary tumors. Metastases are treated with lymph node dissection, irradiation, or both. 13-cis-retinoic acid (1 mg orally every day) plus INF-α (3 million units subcutaneously or intramuscularly every day) may produce a partial response in most patients. Systemic chemotherapy combinations that include cisplatin may also be palliative in some patients. Prevention As the vast majority of skin cancers are related to chronic UV radiation exposure, patient and physician education could dramatically reduce their incidence. Emphasis should be placed on preventive measures beginning early in life. Patients must understand that damage from UV-B begins early, despite the fact that cancers develop years later. Regular use of sunscreens and protective clothing should be encouraged. Avoidance of tanning salons and midday (10 A.M.–2 P.M.) sun exposure is recommended. Precancerous and in situ lesions should be treated early. Early detection of small tumors affords simpler treatment modalities with higher cure rates and lower morbidity. In patients with a history of skin cancer, long-term follow-up for the detection of recurrence, metastasis, and new skin cancers should be emphasized. Chemoprophylaxis using synthetic retinoids is useful in controlling new lesions in some patients with multiple tumors. . Chapter 083. Cancer of the Skin (Part 9) Squamous Cell Carcinoma The natural history of SCC depends on both tumor and host characteristics. Tumors arising on actinically damaged skin. decrease the rate of NMSC in xeroderma pigmentosum. Squamous Cell Carcinoma The therapy of cutaneous SCC should be based on an analysis of risk factors influencing the biologic behavior of the. tumor. These include the size, location, and degree of histologic differentiation of the tumor as well as the age and physical condition of the patient. Surgical excision, MMS, and radiation therapy