Radiation sensitivity and efficacy in aggressive and non-aggressive basal cell carcinoma (BCC) of the skin: Image Guided Superficial Radiation Therapy achieves high rate of local control in sclerosing, infiltrative, morpheaform and micronodular BCC subtypes as well as in non high risk BCCs, an analysis of 7994 BCC lesions.

BackgroundHigh risk (HR) basal cell carcinoma (BCC) subtypes have been associated with high recurrence rates that is felt to be better managed surgically. Specifically, Mohs Micrographic Surgery (MMS) is considered most effective for aggressive HR BCCs and superior to traditional nonsurgical techniques, including radiation. Recently, superficial radiation therapy with high resolution ultrasound image guidance called Image Guided Superficial Radiation Therapy (IGSRT) displayed high local control (LC) rates and is an emerging non-surgical alternative to MMS for non-melanoma skin cancer (NMSC). ObjectivesWe present the largest experience in the USA on treatment of BCCs using IGSRT and specifically evaluate if there are differences in LC between HR BCC versus non-HR subtypes using this technology. MethodsA retrospective analysis was conducted on 7,994 BCC lesions treated with IGSRT in the continental United States. We compared the results of BCCs treated with IGSRT separated by HR vs non HR groups including 339 HR BCC lesions and 7655 non HR BCC lesions. High risk was defined as infiltrative, micronodular, morpheaform, and sclerosing subtypes. Non-HR BCC included superficial, nodular, and not otherwise specified (NOS) subtypes. Local control (LC) rates at two and five years were calculated with actuarial life-table and Kaplan-Meier methods and statistically compared using log rank tests. ResultsIGSRT treatment of the HR BCC group showed no recurrences with two and five-year actuarial and KM LC rates all at 100%. In comparison, the non-HR BCC cohort achieved similar two and five-year actuarial LC rates of 99.71% and 99.24% (KM LC at 99.5% and 99.23%), respectively. No statistical differences in LC rates between the two cohorts (p=0.278 each) resulted. Patients tolerated treatment well with little or rare high grade RTOG toxicity reported in both cohorts. ConclusionHR BCC may be treated just as effectively as low risk BCC using IGSRT and presents a viable alternative to MMS. The targeted approach using IGSRT, incorporating high resolution dermal ultrasound (HRDUS), appear to enhance treatment accuracy and effectiveness demonstrating high LC rates in all subtypes of BCC comparable to MMS and is a viable non-surgical option. Plain language summary Effectiveness of a non-surgical skin cancer treatment using an image guided form of radiation modality on all subtypes of basal cell skin cancerRecent studies using a non-surgical treatment combining low penetrance radiation with ultrasound called Image Guided Superficial Radiation Therapy (IGSRT) showed promise in curing Basal Cell Cancer (BCC) of the skin, which is the most common skin cancer worldwide afflicting millions annually. Recent studies on early stage (I, II) BCCs treated with IGSRT (estimated combined total of [~]1900 BCC cases) appear to rival the best surgical treatment available called Mohs Micrographic Surgery ("Mohs" or MMS). Furthermore, certain subtypes of BCC appear to behave more aggressively with worse outcomes even with surgery and is generally felt inappropriate for radiation treatment. However, BCC subtypes were not specified in previous IGSRT studies. This study presents the largest experience (using medical chart review) in approximately 8000 BCC cases treated by IGSRT across the continental United States separated by aggressive vs non-aggressive subtypes for early stages (I, II) as well as more advanced (stage III) BCC cases to evaluate the efficacy and safety. This study confirms the high cure/control rate and safety of IGSRT for all subtypes of BCC which appear equivalent with Mohs (although the study was not meant to be a head to head comparison of the 2 different modalities). Moreover, the aggressive types of BCC showed similar (if not marginally better) cure rates than the more common non-aggressive BCC subtypes. The potential benefits to patients from this study show there is now a clinically proven non-surgical treatment with the same effectiveness as surgery for the most common cancer on the planet. Key PointsO_LIThis study provides evidence that backs up using IGSRT as a viable treatment option to MMS for both high risk and non-high risk BCC cases, achieving similar local control rates for both groups. C_LIO_LIIt highlights that high risk BCC is more sensitive to radiation therapies such as IGSRT than previously believed, challenging the conventional practice of surgical treatment. C_LI