Dermatology: Practical and Conceptual Image Letter | Dermatol Pract Concept. 2023;13(1):e2023059 1 Diving Into the Blue: A Case of Melanoma Arising in a Giant Congenital Blue Nevus During Pregnancy Alex Curti1, Simonetta Piana2, Maria Banzi3, Fabio Castagnetti4, Michela Lai1,5,6, Caterina Longo1,5 1 Department of Dermatology, University of Modena and Reggio Emilia, Modena, Italy 2 Pathology Unit, Azienda Unità Sanitaria Locale - IRCCS di Reggio Emilia, Reggio Emilia, Italy 3 Medical Oncology Unit, Azienda Unità Sanitaria Locale - IRCCS di Reggio Emilia, Italy 4 Breast Surgery Unit, Azienda Unità Sanitaria Locale - IRCCS di Reggio Emilia, Italy 5 Centro Oncologico ad Alta Tecnologia Diagnostica, Azienda Unità Sanitaria Locale - IRCCS di Reggio Emilia, Italy 6 Clinical and Experimental Medicine PhD Program, University of Modena and Reggio Emilia, Modena, Italy Citation: Curti A, Piana S, Banzi M, Castagnetti F, Lai M, Longo C. Diving Into The Blue: A Case Of Melanoma Arising In A Giant Congenital Blue Nevus During Pregnancy. Dermatol Pract Concept. 2023;13(1):e2023059. DOI: https://doi.org/10.5826/dpc.1301a59 Accepted: August 23, 2022; Published: January 2023 Copyright: ©2023 Curti 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: Caterina Longo, Centro Oncologico ad Alta Tecnologia Diagnostica - Dermatologia, Azienda Unità Sanitaria Locale – IRCCS di Reggio Emilia, Reggio Emilia, Italy. Department of Dermatology, University of Modena and Reggio Emilia, Italy. Phone: +390522295611 E-mail: longo.caterina@gmail.com Case Presentation Melanoma is the most frequent malignancy in pregnancy, accounting for 31% of malignant tumors diagnosed during gestation [1]. We report a case of a 28-year-old woman, pregnant at the 34th week of gestation, who had periodical skin check examination for the presence of a congenital blue nevus involving the neck, the scalp and the preauricular region (Figure 1A). During pregnancy, she self-reported the devel- opment of a solid subcutaneous 4.2 cm firm mass on her right latero-cervical region (inset). Histological examination was consistent with mela- noma developed on a congenital melanocytic blue nevus (Figure 1B). The marked melanocytic atypia and the high mitotic count allowed the differential diagnosis with a proliferative nodule in congenital nevi. At the molecular analysis, the melanoma showed no alterations in BRAF, c-Kit and all RAS. GNAQ and GNA11 mutation state was not evaluated since it is not part of our standard of care panel. After the induction of delivery at the 38th week of gesta- tion, histological examination of the placenta ruled out pos- sible secondarism to the fetus. A total body CT scan of the patient identified four solid lesions in the liver, histologically confirmed as metastasis. Fi- nal diagnosis of stage IV melanoma was made. After a multidisciplinary discussion of the case, immuno- therapy with nivolumab was started at a dosage of 240 mg iv every two weeks. After one year of systemic treatment, the patient achieved a complete response and since the response is still main- tained after four years follow up, immunotherapy has now been discontinued. 2 Image Letter | Dermatol Pract Concept. 2023;13(1):e2023059 Teaching Point European guidelines for the management of melanoma during pregnancy are still lacking, hence it is extremely challenging to decide the correct diagnostic and therapeu- tic approach to adopt. A multidisciplinary management is warranted and each case must be discussed on an individual patient-tailored basis [2]. References 1. Kyrgidis A, Lallas A, Moscarella E, Longo C, Alfano R, Ar- genziano G. Does pregnancy influence melanoma prognosis? A meta-analysis. Melanoma Res. 2017;27(4):289–299. DOI: 10.1097/CMR.0000000000000334. PMID: 28430756. 2. Ribero S, Longo C, Dika E, et al. Pregnancy and melanoma: a European-wide survey to assess current management and a critical literature overview. J Eur Acad Dermatol Venereol. 2017;31(1):65-69. DOI: 10.1111/jdv.13722. PMID: 27231086. Figure 1. (A) Clinical picture of a giant congenital blue nevus, involving the right latero-cervical region and extending to preauricular skin and to the scalp; (inset) clinical picture showing a firm solid mass, developed during pregnancy on the right latero-cervical region on con- genital blue nevus. (B) Skin and soft tissue biopsy specimen showing intensely pigmented fusiform proliferation of melanocytes with mitotic figures and necrosis, finding consistent with melanoma.