2.3.3.2 Treatment
The treatment plan of non-melanoma skin cancer should be selected based on factors such as age，tumor stage and location，risk of recurrence，patient expectations，and potential adverse effects.The treatment of non-melanoma skin cancer can be divided into surgical treatment and non-surgical treatment.Surgical treatment includes standard excision，Mohs micrographic surgery，electrodesiccation and curettage.Non-surgical treatments include radiotherapy，cryotherapy，topical therapy，systemic therapy，and photodynamic therapy.Among them，surgery is cornerstone of non-melanoma skin cancer treatment.Table 2-3 shows the cancer risk assessment.
Table 2-3 Differentiating low-risk and high-risk basal and squamous cell carcinomas based on guidelines from the NCCN*
Continued
*National Comprehensive Cancer Network.National clinical practice guidelines in oncology：squamous cell skin cancer（version Ⅰ.2017）.
†Mask area of face refers to central face，eyelids，eyebrows，periorbital，nose，lips，chin，mandible，ears，preauricular/postauricular，and temple.
‡Aggressive histologic subtypes for basal cell carcinoma include morpheaform，basosquamous，sclerosing，mixed infiltrative，and micronodular.Aggressive histologic subtypes for squamous cell carcinoma include adenoid（acantholytic），adenosquamous，desmoplastic（showing mucin production），and metaplastic（carcinosarcomatous）.
1.Low-risk tumors
（1）Surgical treatment：Standard excision is preferred for low-risk tumors，with postoperative margin assessment（4 mm for basal cell carcinomas and 4-6 mm for squamous cell carcinomas）.If there is a positive margin，the resection should be expanded according to the situation and supplemented with radiotherapy.
Electrodesiccation and curettage can also be used to treat low-risk tumors.Using mechanical debridement and electrocoagulation to completely disintegrate and remove visible tumors，the advantage is that the surgical procedure is fast and costeffective.However，the effects of electrodesiccation and curettage highly depend on operator and location.For example，tumors in the hair-bearing area（scalp，pubic，axilla，and beard area）may invade the hair follicle.The electrodesiccation may result in incomplete removal of the tumor and cause tumor recurrence.In addition，electrodesiccation and curettage have great trauma to the skin，leaving obvious scars.Therefore，tumors located in cosmetically sensitive areas are not suitable for electrodesiccation and curettage.
（2）Non-surgical treatment：If surgical treatment cannot be performed according to the patients'condition，non-surgical treatment can be selected，including radiotherapy，topical therapy，photodynamic therapy，cryotherapy，etc.
Radiotherapy is a commonly used non-surgical therapy，which can be used to treat highand low-risk tumors when surgery can't be performed，and can be used as adjuvant therapy to surgical treatment.However，due to the long-term chronic toxic side effects of radiotherapy，radiotherapy is generally recommended for elderly patients（＞60 years old）.
Topical therapy is currently the most commonly used non-surgical therapy.5-fluorouracil and imiquimod are used topically in tumor lesions.These two drugs can promote the apoptosis of tumor cells by inhibiting DNA synthesis and activating cell-mediated immune response.Topical therapy has significant effect on superficial low-risk primary tumors，and is particularly suitable for patients with multiple skin lesions throughout the body.In addition，topical therapy has less damage to the skin than surgical treatment，and retains the aesthetic function of the skin to the greatest extent.However，the drawbacks to topical therapy are that they require long and multiple treatments，so the compliance requirements of patients are very high.(https://www.daowen.com)
Photodynamic therapy is also one of the commonly used non-surgical therapies，and it has a significant effect on superficial low-risk primary tumors.Photodynamic therapy often causes patient intolerance due to pain，chronic open wounds，and pigmentation.
Cryotherapy refers to the use of repetitive freeze-thaw cycles to locally destroy malignant skin cells under liquid nitrogen at-50℃.It can also effectively treat superficial low-risk primary tumors.The cryotherapy process is fast，costeffective and does not require local anesthesia.However，cryotherapy can cause localized persistent edema，neuralgia，scarring and pigmentation，so the use of cryotherapy is not as extensive as the above two therapies.
2.High-risk tumors
For high-risk non-melanoma skin cancers，the gold standard of treatment is Mohs micrographic surgery.Studies have shown that Mohs micrographic surgery has a very high cure rate and low mortality，and can preserve the integrity of the tissue to the greatest extent.If Mohs micrographic surgery cannot be performed，standard excision can also be considered，but the margin assessment should be expanded to 10 mm.For patients who cannot perform surgery，the aforementioned non-surgical treatment options can be considered，but the risk of poor efficacy and tumor recurrence needs to be accepted.
3.Recurrence，metastatic and advanced tumors
Tumors with local recurrence without evidence of distant metastasis should be treated as high-risk tumors.For locally and distantly metastasized tumors，treatment plans should be jointly developed through multidisciplinary collaboration.On the basis of surgical treatment as much as possible，a variety of adjuvant therapy are carried out.Adjuvant therapy options include radiotherapy，chemotherapy and Hedgehog pathway inhibitors.For patients with advanced tumors that cannot be operated，full consideration should be given to the patient's own situation，with the purpose of maximizing symptom relief and ensuring quality of life，and selecting appropriate systemic treatment options for patients，such as radiotherapy，chemotherapy，and Hedgehog pathway inhibitors.