Yu L, Oh C, Shea CR. The Treatment of Non-Melanoma Skin Cancer with Image-Guided Superficial Radiation Therapy: An Analysis of 2917 Invasive and In Situ Keratinocytic Carcinoma Lesions. Oncology and Therapy. 2021;9(1):153-166. doi:10.1007/s40487-021-00138-4.
Superficial Radiation Therapy may be beneficial as first line option for early stage nonmelanoma skin cancers (NMSCs).
Clinical Pearls
This was a retrospective, observational real-world case series of 2917 American Joint Committee on Cancer 8th edition (AJCC 8) stage 0-II nonmelanoma skin cancers (NMSC) treated with superficial radiation therapy (SRT) from 2017 to 2020.
2897 out of 2917 NMSCs (99.3%) with a median tumor diameter of 1 cm achieved local tumor control within a mean of ~20 treatment fractions over a mean of ~7 weeks with radiation energy and dose determined by pre-treatment ultrasound imaging.
Discussion:
Nonmelanoma skin cancers (NMSCs) such as cutaneous squamous cell carcinoma (cSCC) and basal cell carcinoma (BCC) account for a majority of skin cancers that patients have and dermatologists treat per year, affecting over 3 million patients annually. If caught early, NMSCs are usually curable with surgical resection and close follow-up. However, even lower-risk lesions may not be optimal for surgical intervention depending on patient characteristics such as age or comorbidities, lesion location, or even patient preference. Superficial radiation therapy has been investigated as an alternative treatment option for patients
This retrospective, observational, real-world case series followed 1632 patients treated with a mean radiation dose of 5219.9 (standard deviation ± 224.47) cGy. Despite guidelines changes between 2018 (Lesion depth: <1.5mm, 255 cGy x 20 total fractions 50 kV, 70 kV if > 1.5mm; <2cm 245 cGy 4 times a week for 20 fractions; >4cm, 240 cGY four times a week for 25 fractions) and 2019 (most common protocol: 245-270 cGy 3-4 times weekly using 50, 70 or 100 kV), therapeutic regimens were tailored based on lesion depth, anatomic location, and ultrasound findings. Patients unable to follow these protocols were excluded from the study.
Among 2917 NMSCs treated (BCC, n=1406, cSCC, n=920, cSCCis, n=603; lesions were not mutually exclusive on histology) from 1632 patients with a mean age of 73, 98.8% did not have evidence of residual disease after a mean treatment dose of 5219.9 cGy (±224.47) at their last follow-up (mean number of treatments, 20.1(±0.71); mean treatment duration: 7.1(±1.55) weeks). Less than 1% of treated lesions had toxicity rated severe and mortality rate of the treatment group was ~2.5% and deemed similar to general population of similar age. Patients who were followed up for 1 year post treatment had similar survival outcomes as those who were not.
The authors note that this study may underestimate SRTs efficacy given the 20 patients who did not achieve clearance had a larger NMSC burden and that analysis on a lesion-by-lesion case lead to a higher 99.3% control rate. They also highlight the tissue-sparing properties of SRT given that 58% of NMSCs treated were on cosmetically-sensitive areas of the head and neck.
Limitations of this study include its retrospective, observational nature, exclusion of patients who were also not amenable to SRT and lack of control with traditional surgical management. However, these findings may serve as a catalyst for further prospective (potentially randomized, controlled) clinical trials comparing Mohs micrographic surgery and SRT.
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