Locally advanced basal cell carcinoma treated with sonidegib: in vivo monitoring with line-field confocal optical coherence tomography

Background: Hedgehog pathway inhibitors, including sonidegib and vismodegib, represent the treatment strategy for 'difficult-to-treat' basal cell carcinoma (BCC), encompassing, among others, locally advanced (laBCC) and metastatic BCC. Assessment of therapy response is challenging due to the presence of telangiectasia and scar tissue at the area of the BCC lesion. Line-field confocal optical coherence tomography (LC-OCT) is a new noninvasive imaging technique that provides high-resolution visualization of skin structures. Objectives: To investigate the value of LC-OCT for the assessment of laBCC response to sonidegib therapy. Methods: We retrospectively included patients with laBCC treated with sonidegib in the period from May 2020 to May 2023. Patients with laBCC underwent LC-OCT at baseline before starting sonidegib, and after sonidegib discontinuation when clinical complete response (CR) was reached. A subset of patients underwent LC-OCT assessment during sonidegib therapy to assess tumour persistence. Results: Twenty laBCCs in 20 patients 4 women, 16 men; mean (SD) age 76 (18) years treated with oral sonidegib 200 mg daily were included in the study. Ten patients obtained an apparent clinical CR; LC-OCT imaging confirmed CR in 7/10 patients (70%), while in the remaining patients (3/10, 30%) LC-OCT revealed findings indicative of BCC non-CR. Ten patients were continuing sonidegib treatment: in this group LC-OCT revealed findings suggestive of BCC persistence in all 10 patients (100%). Conclusions: In this study we provide preliminary results of the beneficial use of LC-OCT in the management of patients with laBCC treated with sonidegib therapy.