Dermatology: Practical and Conceptual Research Letter | Dermatol Pract Concept. 2024;14(3):e2024173 1 Non-Invasive Imaging of Basal Cell Carcinoma with Neuroendocrine Differentiation with Line-Field Confocal Optical Coherence Tomography Lorenzo Barbarossa1, Arianna Lamberti1, Costantino Ricci2,3, Mariano Suppa4,5, Elisa Cinotti1, Pietro Rubegni1, Linda Tognetti1 1 Dermatology Section, Department of Medical, Surgical, and Neurological Sciences, Santa Maria Alle Scotte Hospital, Siena, Italy 2 Pathology Unit, Maggiore Hospital, AUSL Bologna, Bologna, Italy 3 Department of Medical and Surgical Sciences (DIMEC), University of Bologna, Bologna, Italy 4 Department of Dermatology, Hôpital Erasme, HUB, Université Libre de Bruxelles, Belgium 5 Department of Dermatology, Institut Jules Bordet, HUB, Université Libre de Bruxelles, HUB, Brussels, Belgium Key words: basal cell carcinoma, LC-OCT, non‐invasive, imaging, neuroendocrine differentiation Citation: Barbarossa L, Lamberti A, Ricci C, et al. Non-Invasive Imaging of Basal Cell Carcinoma With Neuroendocrine Differentiation With Line-Field Confocal Optical Coherence Tomography. Dermatol Pract Concept. 2024;14(3):e2024173. DOI: https://doi.org/10.5826 /dpc.1403a173 Accepted: March 13, 2024; Published: July 2024 Copyright: ©2024 Barbarossa et al. This is an open-access article distributed under the terms of the Creative Commons Attribution- NonCommercial License (BY-NC-4.0), https://creativecommons.org/licenses/by-nc/4.0/, which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original authors and source are credited. Funding: None. Competing Interests: None. Authorship: All authors have contributed significantly to this publication. Corresponding Author: Lorenzo Barbarossa, MD, Dermatology Section, Santa Maria alle Scotte Hospital, Viale Mario Bracci, 53100, Siena – Italy. Email: lorenzobarbarossa1993@gmail.com Introduction Basal cell carcinoma (BCC) is the most frequent tumor with incidence increasing worldwide. It can exhibit different and bizarre differentiation, among which squamous (basosqua- mous BCC), sarcomatoid, adnexal (follicular, sebaceous, and apocrine/eccrine), and -rarely- a neuroendocrine differ- entiation (BCC-NED) [1,2]. Among the reported cases of BCC-NED, the majority arose on the head and neck areas (especially cheek and lower eyelid), followed by the thigh, inguinal region and umbilicus [1,2]. Case Presentation A 44-year-old man presented for routine skin check screening: a scar-like lesion was noted on the upper back (Figure  1A), firm and indurated at palpation; the patient referred only to had memory of an epidermal cyst in that area. An examination by line-field confocal optical coher- ence tomography (LC-OCT), a recently developed tech- nique able to provide, in real time, vertical and horizontal skin images with cellular resolution up a depth of 500 µm (lateral FOV of 1200 µm) was required to rule-out inflamed 2 Research Letter | Dermatol Pract Concept. 2024;14(3):e2024173 dermatofibroma [3,4]. LC-OCT scan revealed multiple lob- ules separated from the epidermis (Figure 1, D-F) with dense cellularity (ie millefeuille pattern) and well-defined margins, dense connective strands and dilated capillary and dermal vessels. In superficial dermis, lobules were smaller and tightly disposed (Figure 1E), while in deep dermis were larger and interspersed with microcystic areas (Figure 1, D and F). BCC was suspected and surgical excision planned. The histologic exam showed nodular BCC infiltrating of the subcutaneous tissue (thickness: 3.5 mm), with cytologic features sugges- tive of neuroendocrine differentiation (salt-and-pepper chro- matin, no nucleoli, high N/C ratio and nuclear molding); the tumor diffusely stain for chromogranin (granular and cytoplasmatic) but turned out negative for synaptophysin (Figure  1I), cytokeratin 20, and NSE, thus allowing us to make the diagnosis of BCC-NED. Conclusions The BCC-NED variant is a very rare instance. Not uncom- monly, BCC-NED has been reported associated to scars, suggesting the surgical trauma as potential trigger [3]. Clin- ical features may be misleading (ie scar-like lesions) and the dermoscopic features (in-focus arborizing vessels, cobble- stone appearance of microcysts) are shared with other BCC subtypes. Thus, histological and immunohistochemical anal- yses are required for the diagnosis, showing neuroendocrine cytological features and diffuse stain for at least one neuro- endocrine markers [3]. To date, LC-OCT has been successfully employed to de- tect several epidermal and/or upper dermal alterations [3]. In particular, our group demonstrated that LC-OCT was able to realize a “virtual biopsy” in basal cell carcinoma subtypes [4]. Here in this case, with an atypical picture and confounding patient history, the in vivo LC-OCT examination allowed us to detect specific BCC features (eg BCC- lobules with millefeuille pattern, microcysts, fibrotic structures) and to individuate the lesion depth exten- sion. Moreover, a thorough co-localization of the LC-OCT image with the exact lesional point of the dermoscopic frame was possible (ie red bar, Figure 1). In conclusion, we report on a rare case of BCC-NED with LC-OCT. This device is thus proposed as a rapid and easy-to-use tool to support clinicians in orienting the di- agnostic suspect and the appropriate lesion management. Moreover, thanks to a co-localization software that matches Figure 1. Clinical appearance at presentation time. (A) A scar-like lesion, 10.5 x 6.20 mm, located in right scapular region. (B) Polarized dermoscopy ×40 enlargement) highlights an oval lesion character- ized by a brownish/yellowish peripheral pigmentation with a focal grayish spot and a whitish center with cobblestone-like pattern. (C) Non-polarized dermoscopy. (×40x enlargement) highlighted multiple in-focus arborizing vessels (red arrow) arranged in a radial pattern. Each vertical LC-OCT image is paired with a corresponding dermoscopic frame. (D-F) The red line inside the dermoscopic frame indicates the exact posi- tion of the probe tip inside the lesion and corresponds to the 1.2- mm field of view on a vertical plane of the LC-OCT probe. Navigating inside the lesion, multiple lobules (asterisks) separated from the epidermis were visible in all lesional point with dense cellularity (ie hyperreflective small structures, millefeuille pattern) delimited by well-defined margins; hyperreflective linear structures corresponding to connective strands (arrows) and non-reflective roundish structures corresponding to dilated capillary and dermal vessels (v) were also visible. Lobules were smaller in size and tightly disposed in superficial dermis, interspersed with microcystic areas (arrowheads) and larger in deep dermis. (G) H&E staining (×40) showed BCC lobules characterized by basaloid epithelium with typical palisade form and cleft from the adjacent tumor stroma, infiltrating the deep dermis. (H) Immunohistochemistry analysis showed strong chromogranin-positivity was present inside the lobular and microcystic structures, while (I) synaptophysin staining was negative. Research Letter | Dermatol Pract Concept. 2024;14(3):e2024173 3 the LC-OCT with the dermoscopic images, this device can be employed for a real time for preoperative mapping of surgi- cal margins [5]. References 1. Houcine Y, Chelly I, Zehani A, et al. Neuroendocrine differen- tiation in basal cell carcinoma. J Immunoassay Immunochem. 2017;38(5):487-493. DOI: 10.1080/15321819.2017.1331170. PMID: 28548901. 2. Chung IY, McKelvie P, Chen Y. Eyelid basal cell carcinoma with neuroendocrine differentiation: a case report and literature review. Orbit. 2021;40(4):316-319. 3. Monnier J, Tognetti L, Miyamoto M, et al. In vivo characteri- zation of healthy human skin with a novel, non-invasive imag- ing technique: line-field confocal optical coherence tomography. J Eur Acad Dermatol Venereol. 2020;34(12):2914-2921. 4. Suppa M, Fontaine M, Dejonckheere G, et al. Line-field con- focal optical coherence tomography of basal cell carcinoma: a descriptive study. J Eur Acad Dermatol Venereol. 2021;35(5): 1099-1110. 5. Venturi F, Pellacani G, Farnetani F, Maibach H, Tassone D, Dika E. Noninvasive diagnostic techniques in the preoperative setting of Mohs micrographic surgery: A review of the litera- ture. Dermatol Ther. 2022 Nov;35(11):e15832. doi: 10.1111 /dth.15832.