Dermatology: Practical and Conceptual Research Letter | Dermatol Pract Concept. 2023;13(2):e2023068 1 Hypomelanotyc Basomelanocytic Tumor Cesare Massone1, Sanja Javor1, Stefano Chiodi2, Simona Sola3 1 Dermatology Unit, E.O. “Ospedali Galliera”, Genoa, Italy 2 Plastic Surgery, E.O. “Ospedali Galliera”, Genoa, Italy 3 Surgical Pathology, E.O. “Ospedali Galliera”, Genoa, Italy Key words: basal cell carcinoma, melanoma, collision tumor, basomelanocytic tumor Citation: Massone C, Javor S, Chiodi S, Sola S. Hypomelanotyc Basomelanocytic Tumor. Dermatol Pract Concept. 2023;13(2):e2023068. DOI: https://doi.org/10.5826/dpc.1302a68 Accepted: July 14, 2023; Published: April 2023 Copyright: ©2023 Massone 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: Cesare Massone, MD, Dermatology Unit - Ospedali Galliera. Via Volta 6, 16128, Genova (IT). Phone: 0039 010 5632 4271. E-mail: cesare.massone@galliera.it Introduction Dermoscopic diagnosis of collision tumor (CT) is a challenge. Zaballos et al recently found that the most frequent CTs are: basal cell carcinoma (BCC)-seborrheic keratosis (37.9%), BCC-melanocytic nevus (19.9%), and melanoma-seborrheic keratosis (6.8%).1 The collision BCC-melanoma is very rare (reported under the terms “basomelanocytic tumor (BMT)”) and its dermoscopic features have been described in only few cases [1,3-6]. Case Presentation A 58-year-old woman presented with an enlarging ulcerated erythematous-brown plaque of 16 x 8 mm on her left leg ap- peared almost six months before. The clinical diagnosis was ulcerated BCC. Dermoscopy showed an asymmetric poly- chromatic multicomponent pattern with shiny white struc- tures, structureless blue-grey areas, grayish peppering, milky red areas, atypical vessels, ulceration and crusts (Figure 1, A and B). She denied previous history of skin cancer. Histopathological examination showed an irregular hyperplastic epidermis and, in the dermis, BerEp4-positive large nests (Figure 1F) composed by basaloid keratinocytes with palisading of cells at the periphery and clefts with the surrounding stroma (Figure 1, C-E and I). Inside some nests and in the dermis was present a second cell population of spindle cells and also dentritic cells that stained positive for Melan-A, S100 and HMB-45 (Figure 1, G and H). An in- creased number of single atypical melanocytes at the der- moepidermal junction was also observed. A BMT (BCC and pT2b melanoma of 1mm Breslow thickness; BRAF WT) was diagnosed. Wide surgical excision and lymph node biopsy were performed with no evidence of metastatic cells, also at staging investigations (pT2b N0 M0). After 24-months follow-up the patient is still without evidence of secondary disease. 2 Research Letter | Dermatol Pract Concept. 2023;13(2):e2023068 Figure 1. (A) Erythematous violaceous plaque of 16 x 8 mm with erosive surface on the lower limb of atypical morphology and multicolor appearance. (B) Asymmetric polychromatic multicomponent pattern with shiny white structures, structureless blue-gray areas, milky red areas, atypical vessels, ulceration and crusts without clearly pigment network at the periphery. (C) Irregular hyperplastic epidermis and, in the dermis, large nests composed by basaloid keratinocytes with palisading of cells at the periphery, clefts with the surrounding stroma and inflammatory infiltrate of the perilesional area (H&E; original magnification 5x). (D) Irregular hyperplastic epidermis and, in the dermis, large nests of basaloid cells with a second cell population of spindle cells and dentritic cells. Heavy inflammatory infiltrate of the perilesional area (H&E; original magnification 5x). (E). Higher magnification of the basaloid cells, atypical spindle and dentritic cells with mitotic figures (H&E; original magnification 20x). (F) Strong immunoreactivity for BerEp4 evidenced the basal cell carcinoma component (original magnifi- cation 5x). (G) Melan-A stained the atypical melanocytes of the melanoma component. An increased number of single atypical melanocytes at the dermoepidermal junction and in the dermis was also observed (original magnification 5x). (H) HMB-45 stained the atypical melanocytes of the melanoma component. An increased number of single atypical melanocytes at the dermoepidermal junction and in the dermis was also observed (original magnification 5x).(I) Large nest of basaloid cells with palisading at the periphery (original magnification 5x). Conclusions Histologically, BMT may result by a variety of modality of “collisions” like colonization, combined, biphasic, bipheno- typic, or intermingled neoplasms [2]. Pathogenetic explanations are different and refer to: the field cancerization theory (proliferation of two distinct clones resulting in the development of two intermingled neo- plasms); the tumor divergent theory (biphasic neoplasm with two neoplastic populations); tumor convergent theory (two phenotypically different cell populations derive from a com- mon progenitor stem cell). BMT has also been considered a low-grade malignancy with a dual phenotype; in fact, the histologic merging between two malignant cell types argues against a simple collision [2,3]. To our knowledge, about 50 cases of BMT have been reported in the literature [1,3-6]; dermoscopy has been de- scribed in details in only 9 cases (Table 1). One of the two tumors is usually recognized upon dermoscopy when one of the two component is prevalent, but usually the exact diag- nosis of BMT is difficult. Reflectance confocal microscope (RCM) can be highly useful in the diagnosis [4]. Moreover, BMT can occur in patient with basal cell nevus syndrome or xeroderma pigmentosum, therefore an accurate examination of the patients is needed [6]. Our patient presented an ulcer- ated hypomelanotic BMT, representing a further pitfall. The biologic behavior of BMT is still not clearly un- derstood. According to Amin et al distant metastases are uncommon and combined cutaneous tumors may have a better prognosis when compared to similarly staged conven- tional melanomas [2]. In contrast, Erickson et al, reported a 56-year-old man with BMT of the scalp who developed a subsequent metastasis [2]. In conclusion, BMT represent a clinical diagnostic chal- lenge and suspicious lesions should be observed accurately with dermoscopy and also with RCM, when available. Research Letter | Dermatol Pract Concept. 2023;13(2):e2023068 3 References 1. Zaballos P, Álvarez Salafranca M, Medina C, et al. The Use- fulness of Dermoscopy for the Recognition of Malignant Col- lision Tumors. Dermatology. 2022;238(1):132-139. DOI: 10.1159/000514583. PMID: 33789291. 2. Cota C, Saggini A, Lora V, et al. Uncommon Histopathological Variants of Malignant Melanoma: Part 1. Am J Dermatopathol. 2019;41(4):243-263. DOI: 10.1097/DAD.0000000000001218. PMID: 30024414. 3. Busam KJ, Halpern A, Marghoob AA. Malignant melanoma metastatic to a basal cell carcinoma simulating the pattern of a basomelanocytic tumor. Am J Surg Pathol. 2006;30(1):133-136. DOI: 10.1097/01.pas.0000179118.76904.02. PMID: 16330954. 4. Moscarella E, Rabinovitz H, Oliviero MC, et al. The role of reflectance confocal microscopy as an aid in the diagnosis of collision tumors. Dermatology. 2013;227(2):109-117. DOI: 10.1159/000351771. PMID: 24080548. 5. Blum A, Siggs G, Marghoob AA, et al. Collision skin lesions- results of a multicenter study of the International Dermoscopy Society (IDS). Dermatol Pract Concept. 2017;7(4):51-62. DOI: 10.5826/dpc.0704a12. PMID: 29230351. PMCID: PMC5720595. 6. Bostanci S, Akay BN, Kirmizi A, Okcu Heper A, Farabi B. Basosquamous carcinoma and melanoma collision tumor in a child with xeroderma pigmentosum. Pediatr Derma- tol. 2020;37(2):390-392. DOI: 10.1111/pde.14097. PMID: 31957124. Table 1. Dermoscopic features of the basomelanocytic tumors reported in the literature [1,3-6]. Age/sex Location Clinical diagnosis Collision Dermoscopy 70-year-old man face lentigo maligna melanoma BCC – lentigo maligna melanoma Annular granular pattern with rhomboid structures and a dark blotch; large blue-gray ovoid nests with leaf-like structures 69-year-old man postauricular region BCC metastatic melanoma colliding with BCC Multilobulated bluish nodule with a shiny surface, fine blood vessels and large gray-blue ovoid structures. 70-year-old man frontoparietal region Lentigo maligna BCC- lentigo maligna A flat brownish asymmetric lesion with an irregular pigmented network, whitish areas, vessels with linear or arciform shapes and a well-defined, darker area showing four colors (blue, black, white ⁄ grey, red) and black, bluish rounded structures; scales and an erosive site, as well as numerous vessels with arboriform shape; projections of bulbous shape reminiscent of leaf-like structures. 74-year-old man head/neck BCC- lentigo malignaa BCC- lentigo maligna Pink-white area with arborizing vessels and a pseudo network with asymmetrically pigmented follicular openings. na na lentigo maligna BCC – lentigo maligna Pigmented follicles and destroyed follicle with patchy pigmentation; arborizing vessels and pigmented blue- grayish globules 60-year-old man Frontal region Melanoma BCC – lentigo maligna melanoma Multi-component pattern with multiple blue-gray spots, hypochromic area, shiny white streaks and amorphous areas, in addition to an atypical vascular pattern 60-year-old man Left lumbar region Melanoma and BCCa BCC – melanoma in situ Asymmetric lesion with multicomponent pattern, atypical pigment network irregular globules in the periphery, multiple colors, particularly a blue coloration in the center- right of the lesion 13-year-old boy with a history of XP-C right jawline Melanoma BCC – nodular melanoma Ulcerated lesion showed chaos of colors including pink, white, black, gray, and blue structureless areas, gray dots, linear, looped, and serpentine vessels, ulceration, hemorrhage, keratin, scale, and fiber sign 48-year-old man with with basal cell nevus syndrome Back BCC? Melanoma? BCC – melanoma in situ Pink structureless area in the center with short, fine telangiectasias and an atypical network at the periphery BCC = Basal cell carcinoma; na = not available; XP = xeroderma pigmentosum. adiagnosed with the aid of reflectance confocal microscopy.