The management of SCC in situ (Bowen disease) is similar to good-risk SCC. However, since it is noninvasive, surgical excision, including Mohs micrographic surgery, is usually not necessary. In addition, high complete response (CR) rates are achievable with photodynamic therapy (PDT). In a multicenter trial, 229 patients (209 evaluated in the per-protocol/per-lesion analysis) were randomly assigned to receive PDT (methyl aminolevulinate + 570–670 nm red light; n = 91), placebo cream with red light (n = 15); or treatment by physician choice (cryotherapy, n = 77; topical 5-fluorouracil, N = 26). The sustained complete clinical response rates at 12 months were 80%, 67%, and 69% in the three respective active therapy groups (P = .04 for the comparison between PDT and the two combined physician-choice groups).[Level of evidence 1iiDii] The cosmetic results were best in the PDT group. (For comparison, the CR rates at 3 months for PDT and placebo/PDT were 93% and 21%, respectively.)
Treatment for Recurrent Squamous Cell Carcinoma of the Skin
SCCs have definite metastatic potential, and patients should be followed regularly after initial treatment. Overall, local recurrence rates after treatment of primary SCCs ranged from about 3% to 23%, depending upon anatomic site. About 58% of local recurrences manifest within 1 year, 83% within 3 years, and 95% within 5 years. The metastatic rate for primary tumors of sun-exposed skin is 5%; for tumors of the external ear, 9%; and for tumors of the lip, 14%. Metastases occur at an even higher rate for primary SCCs in scar carcinomas or in nonexposed areas of skin (about 38%). About 69% of metastases are diagnosed within 1 year, 91% within 3 years, and 96% within 5 years. Tumors that are 2 cm or larger in diameter, 4 mm or greater in depth, or poorly differentiated have a relatively bad prognosis  and even higher local recurrence and metastasis rates than those listed. Reported rates also vary by treatment modality, with the lowest rates associated with Mohs micrographic surgery, but at least some of the variation may be the result of patient selection factors; no randomized trials directly compare the various local treatment modalities.
Recurrent nonmetastatic SCCs are considered high risk and are generally treated with excision, often using Mohs micrographic surgery. Radiation therapy is used for lesions that cannot be completely resected.
As is the case with BCC, patients who develop a primary SCC are also at increased risk of subsequent primary skin cancers because the susceptibility of their sun-damaged skin to additional cancers persists.[15,16]
Treatment for Metastatic Squamous Cell Carcinoma (or Advanced Disease Untreatable by Local Modalities)
As is the case with BCC, metastatic and far-advanced SCC is unusual, and reports of systemic therapy are limited to case reports and very small case series with tumor response as the endpoint.[Level of evidence 3iiiDiv] Cisplatin-based regimens appear to be associated with high initial tumor response rates.[17,18] High response rates have also been reported with the use of 13-cis-retinoic acid plus interferon-alpha-2a. Since there is no standard therapy, clinical trials are appropriate if available. Information about ongoing clinical trials is available from the NCI Web site.