Dermatology: Practical and Conceptual Research Letter | Dermatol Pract Concept. 2023;13(1):e2023038 1 Basal Cell Carcinomas Presenting as Flat Pigmented Macules on the Face Mimicking Lentigo Maligna on Dermoscopy: A Case Series. Cristian Navarrete-Dechent1,2, Pablo Uribe1,2, Harold Rabinovitz3, Alvaro Abarzua-Araya1,2, Harald Kittler4 1 Melanoma and Skin Cancer Unit, Department of Dermatology, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile 2 Department of Dermatology, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile 3 Department of Dermatology, Medical College of Georgia, Augusta, GA, USA 4 Department of Dermatology, Medical University of Vienna, Vienna, Austria Key words: dermoscopy, dermatoscopy, basal cell carcinoma, lentigo maligna, melanoma, face Citation: Navarrete-Dechent C, Uribe P, Rabinovitz H, Abarzua-Araya A, Kittler H. Basal Cell Carcinomas Presenting as Flat Pigmented Macules on the Face Mimicking Lentigo Maligna on Dermoscopy: A Case Series. Dermatol Pract Concept. 2023;13(1):e2023038. DOI: https://doi.org/10.5826/dpc.1301a38 Accepted: April 24, 2022; Published: January 2023 Copyright: ©2023 Navarrete-Dechent 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: Cristian Navarrete-Dechent, MD, Department of Dermatology, Escuela de Medicina, Pontificia Universidad Catolica de Chile, Diagonal Paraguay 362, 6th floor, Santiago, Chile 8330077 Phone: +56-2-2435 3574 Email: ctnavarr@gmail.com Introduction Basal cell carcinoma (BCC), the most common type of skin cancer, can usually be diagnosed with dermoscopy with high accuracy [1]. We noted, however, that certain pigmented BCCs (pBCCs) are more difficult to diagnose than others. These challenging pBCCs usually appear as flat, pigmented lesions on the face and mimic lentigo maligna (LM). To bet- ter characterize these types of pBCCs, we retrospectively collected typical cases of this clinical presentation and re- evaluated the dermoscopic findings. Case Presentation Cases were selected retrospectively from databases from Austria, Chile, and the United States. Cases were included if they were clinically pigmented and flat. Most cases were sub- mitted for biopsy with LM in the differential diagnosis. We analyzed both pBCC and LM dermoscopic criteria by two independent investigators (CND and HK). A third reviewer helped solving disagreements (PU or .AA). For reflectance confocal microscopy (RCM) images, we used a wide-probe RCM (Vivascope 1500). Biopsy reports were obtained from clinical records and reviewed by expert dermatopatholo- gists. Finally, we analyzed the dermoscopic images with a previously validated convolutional neural network (CNN) (https://dermonaut.meduniwien.ac.at/ypsono) and recorded the top-1 and top-3 accuracy rates [2]. We found 10 cases of BCCs that mimicked LMs. The mean age at diagnosis was 73 years (range: 44-87 years) and 6 of the 10 patients were females. All BCCs presented as flat pigmented macules on sun-exposed areas of the face 2 Research Letter | Dermatol Pract Concept. 2023;13(1):e2023038 (Table 1). On dermoscopy, the main feature was a pattern of angulated lines without obliteration of the follicular open- ings, in all cases (Figure 1 and 2). This pattern mimicked the rhomboidal or ‘zig-zag’ pattern of LM. Additionally, all cases had pink areas and lacked the typical vascular pattern of BCC. Shiny white blotches and strands were seen in 4 out of 10 (40%). One case was examined by RCM and showed classic BCC features such as tumor nodules and cords with Table 1. Demographic and tumor characteristics of included cases. Case # Age (y) Gender Subtype Location 1 45 F Superficial Nose 2 72 M Superficial Forehead 3 44 F Superficial Nose 4 54 M Superficial Forehead 5 83 M Infiltrative Cheek 6 74 F Superficial Cheek 7 87 F Superficial and nodular Nose 8 77 F Superficial and nodular Forehead 9 83 F Nodular, multifocal Nose 10 42 M Superficial Cheek M = male; F = female. Figure 1. Basal cell carcinoma presenting as flat pigmented macules. (A) Clinical features of a flat pigmented macule on the nasal supratip. (B) Dermoscopic features showing rhomboidal structures (arrow) and a pink background (asterisk) (polarized light dermoscopy, original magnification x10). Inset shows reflectance confocal microscopy features showing tumor nodules with palisading and clefting (original mag- nification x30). (C) Clinical features of a flat pigmented macule on the right cheek. (D) Dermoscopic features showing rhomboidal structures (arrow), pink background, and shiny white blotches and strands (asterisk) (polarized light dermoscopy, original magnification x10). Research Letter | Dermatol Pract Concept. 2023;13(1):e2023038 3 Figure 2. Basal cell carcinoma presenting as flat pigmented macules. (A) Clinical features of a flat pigmented macule on the right nasal tip. (B) Dermoscopic features showing rhomboidal structures (black arrow) and a pink background with shiny white blotches and strands (asterisk) (Polarized light dermoscopy, original magnification x10). (C) Clinical features of a flat pigmented macule on the left nasal tip. D. Dermoscopic features showing rhomboidal structures (black arrow) and a pink background (asterisk) (Polarized light dermoscopy, orig- inal magnification x10). palisading and clefting. With regard to histopathologic sub- type, six were superficial, two mixed (superficial and nodu- lar), one had an infiltrative component, and one was nodular BCC. The top-1 and top-3 accuracy rates of the CNN were 0% (0 out of 10) and 60% (6 out of 10), respectively. The most common top-1 predictions of the CNN were pigmented actinic keratosis (pAK), melanoma, and solar lentigo. The patients in this manuscript have given written in- formed consent to publication of their case details. Conclusions We characterized a previously undescribed presentation of facial pBCCs mimicking LM. The common confounding fea- ture seen in all cases was angulated lines (ie ‘rhomboidal’, ‘zig-zag’) without involvement of hair follicles. Although all cases were typified by pink structureless areas, none dis- played the typical serpentine and branching vessels of BCC. In our experience, LM only rarely displays pink areas, which could be a clue for the correct diagnosis of BCC. Shiny white blotches and strands also rarely appear on LMs [3]. The poor performance of a previously validated CNN underlines that these pBCCs are difficult to diagnose [2]. Limitations of this study are (1) that we were not able to estimate the frequency of this type of pBCC in clinical practice, (2) that we did not include a control group of other flat pigmented lesions such as pAK or LM, which is the main mimicker, (3) cases were not consecutive and there might be selection and recall bias, (4) no histopathological correlation of the angulated lines in BCCs was available, and (5) no pathology slides review was performed for BCC histopathological subtypes; however, all cases were initially signed by expert dermatopathologists. In summary, when evaluating flat pigmented lesions on the face, pBCC should be included in the differential diag- nosis [4]; especially when seeing angulated lines amidst pink areas with or without shiny white blotches and strands. References 1. Reiter O, Mimouni I, Gdalevich M, et al. The diagnostic accuracy of dermoscopy for basal cell carcinoma: A systematic review and meta-analysis. J Am Acad Dermatol. 2019;;80(5):1380-1388. DOI: 10.1016/j.jaad.2018.12.026. PMID: 30582991. 4 Research Letter | Dermatol Pract Concept. 2023;13(1):e2023038 Blotches and Strands With Nonpigmented Basal Cell Carci- noma: Evaluation of an Additional Dermoscopic Diagnostic Criterion. JAMA Dermatol. 2016;;152(5):546-552. DOI: 10.1001/jamadermatol.2015.5731. PMID: 26792406. PMCID: PMC5037958. 4. Tschandl P, Rosendahl C, Kittler H. Dermatoscopy of flat pigmented facial lesions. J Eur Acad Dermatol Venereol. 2015;29(1):120-127. DOI: 10.1111/jdv.12483. PMID: 24661420. 2. Tschandl P, Codella N, Akay BN, et al. Comparison of the accu- racy of human readers versus machine-learning algorithms for pigmented skin lesion classification: an open, web-based, inter- national, diagnostic study. Lancet Oncol. 2019;20(7):938-947. DOI: 10.1016/S1470-2045(19)30333-X. PMID: 31201137. PMCID: PMC8237239. 3. Navarrete-Dechent C, Bajaj S, Marchetti MA, Rabinovitz H, Dusza SW, Marghoob AA. Association of Shiny White