Collision of a Giant histiocytic sarcoma with a basal cell carcinoma: causality or coincidence?

n 85-year-old woman presented with a 6-month-old tumor n her back that grew to reach 15 cm in diameter. It was ot accompanied by constitutional symptoms or cytopenias. he lesion was exophytic, multinodular, with reddish and hite-yellowish areas (Fig. 1). At the upper pole of the umor, there was a flatter milky red area with regression reas and ovoid nests on dermoscopy, which was histologially confirmed as a basal cell carcinoma (BCC) (Fig. 2 a--c). biopsy of the most voluminous tumor (Fig. 3a) showed derHistiocytic sarcoma is a rare hematologic neoplasm of histiocytic or dendritic origin, with only a few hundred cases reported. It can be seen at any age and appears to have a slight male predominance.1,2 HS commonly presents as a painless solitary mass in an extranodal location (gastrointestinal tract, soft tissue, skin, spleen, or liver). Skin is affected in almost 7% of the cases, with lesions described predominantly as asymptomatic unique plaque and or nodule.1,2 Dermoscopy has been described as homogeneous yellow background with whitish linear stripes, and arborizing vessels on the periphery.3 Primary cutaneous HS usually presents as a localized disease, with a better prognosis than extracutaneous HS, mainly because it benefits from early treatment.1 In contrast, extracutaneous HS has a mortality rate of 58% with a limited response to chemotherapy.4 In our case, given the poor evolution of

Histiocytic sarcoma is a rare hematologic neoplasm of histiocytic or dendritic origin, with only a few hundred cases reported. It can be seen at any age and appears to have a slight male predominance. 1,2 HS commonly presents as a painless solitary mass in an extranodal location (gastrointestinal tract, soft tissue, skin, spleen, or liver). Skin is affected in almost 7% of the cases, with lesions described predominantly as asymptomatic unique plaque and or nodule. 1,2 Dermoscopy has been described as homogeneous yellow background with whitish linear stripes, and arborizing vessels on the periphery. 3 Primary cutaneous HS usually presents as a localized disease, with a better prognosis than extracutaneous HS, mainly because it benefits from early treatment. 1 In contrast, extracutaneous HS has a mortality rate of 58% with a limited response to chemotherapy. 4 In our case, given the poor evolution of our patient, we interpret cutaneous involvement as a result of contiguous extension from the axillary mass, and not as primary cutaneous HS, although both types would be histologically indistinguishable. HS can be associated, with other hematologic malignancies, suggesting that B cells can be transdifferentiated to a malignant histiocyte. 1,2 The collision of an HS with a BCC has not been previously described in the literature. In our case, although it could be coincidental, the presence of a previous BCC in the area could have influenced the HS location. In this sense, three cases  of ''de novo'' Langerhans cell histiocytosis and one case of indeterminate cell histiocytosis located in sites previously occupied by a BCC have been described. BCCs can create a cytokine environment that promotes cellular hyperplasia but also facilitates the recruitment of latent HS. 5 Additionally, HS could have induced the development of a BCC at the site of its contiguous skin involvement, but this is unlikely due to the low growth rate of the BCC, compared to HS. Given the rarity of skin involvement in HS, it is necessary to collect more cases to obtain a detailed understanding of its biological behavior.

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Authors' contributions
Inés Gracia-Darder: Approval of the final version of the manuscript; critical literature review; data collection, analysis, and interpretation; effective participation in research orientation; intellectual participation in propaedeutic and/or therapeutic; management of studied cases; manuscript critical review; preparation and writing of the manuscript; statistical analysis; study conception and planning.
Julián Boix-Vilanova: Approval of the final version of the manuscript; data collection, analysis, and interpretation; effective participation in research orientation; intellectual participation in propaedeutic and/or therapeutic; management of studied cases; manuscript critical review.
Cristina Gómez Bellvert: Approval of the final version of the manuscript; data collection, analysis, and interpretation; effective participation in research orientation; manuscript critical review.
Luis Javier Del Pozo Hernando: Approval of the final version of the manuscript; critical literature review; effective participation in research orientation; intellectual participa-tion in propaedeutic and/or therapeutic; management of studied cases; manuscript critical review.

Dear Editor,
This case report describes a four-year-old child, followed for three years, with normochromic plaques covered by a cluster of follicular openings filled with keratin, comedolike, along a large extension of the right side: cervical and retroauricular regions, trunk, buttocks, lower limb and foot.
The lesions were located along the Blaschko's lines ( Figs. 1 and 2). Dermoscopy showed more clearly the agmi-Study conducted at the Hospital das Clínicas, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil. nated keratotic plugs (Fig. 3). The lesions were present at birth, and those in the cervical region were often the site of inflammation and secondary infection, requiring recurrent cycles of oral antibiotic therapy during follow-up and surgical removal of the inflamed portion. The child had age-appropriate neuropsychomotor development, with no complaints related to other systems and no family history of relevant diseases. There was no ocular, neurological or skeletal involvement.
Nevus comedonicus is a rare type of epidermal nevus, characterized by a developmental change affecting the pilosebaceous unit. The most frequently affected regions are the face, cervical region, and trunk. It affects both sexes equally, can be congenital, and, in most cases, appears in children before the age of ten. 1 It arouses interest due to the scarcity of cases reported in the literature and the diverse clinical presentations, whether as isolated lesions or extensive cases.