Cutaneous Squamomelanocytic Tumor: An Additional Case Report With Dermoscopic Features

To the Editor: We read with interest the case reported by Zipperer et al1 describing the rare association of cutaneous squamous cell carcinoma and melanoma (cutaneous squamomelanocytic tumor, SMT). SMT being extremely rare, we would like to describe an additional case, reporting also its dermoscopic features. A 79-year-old man was referred in January 2022 for a slowly growing keratotic pigmented skin lesion on his left cheek that appeared almost 1 year before and was previously clinically classified as seborrheic keratosis. The patient was in follow-up for folliculotropic mycosis fungoides, diagnosed in 2016 and in complete remission since 2018 without maintenance therapy after 3 cycles of total skin electron beam (total dose: 36 Gy). Last staging investigations with PET in December 2021 were negative for systemic involvement. He was an outdoor worker (farmer) with a negative history of cutaneous carcinoma and he was not taking any drug. At clinical observation a 2.3- × 1.1-cm large dark-brown and red ulcerated nodule was present on his left cheek (Fig. 1). No clinical lesions suspicious of folliculotropic mycosis fungoides were observed, regional lymph nodes were not enlarged, and he did not refer B symptoms. Dermoscopy revealed a central blood crust surrounded by blue–white veil and a structureless violaceous pseudonetwork with atypical vessels, yellow structureless areas and sparse comedo-like openings; at the periphery, a structureless brown area with irregular dots and asymmetrically pigmented follicular openings were present. Histopathology showed a tumor composed by 2 cell populations in close proximity, but with separate boundaries: (1) irregular columns of well-differentiated keratinocytes arising from the epidermis and extending to the upper dermis (2) atypical melanocytes and irregular nests arranged both in single units in all layers of the epidermis and upper dermis. A heavy inflammatory infiltrate was also present in the dermis. The atypical keratinocytes stained positive for pancytokeratin and p40, whereas the atypical melanocytes resulted positive for Melan-A, S100 and SOX-10 (Fig. 2). The tumor was diagnosed as a collision of a G1 squamous cell carcinoma and a T2b melanoma (Breslow 1, 3 mm; 3 mitosis/mm2; BRAF WT). Sentinel node biopsy and further laboratory and staging investigations evidenced no signs of metastatic disease at 9-month follow-up.FIGURE 1.: A, Dark-brown and red ulcerated tumor on the left cheek; (B) dermoscopy shows a central blood crust surrounded by blue–white veil and a structureless violaceous pseudonetwork with atypical vessels and yellow structureless areas; at the periphery a structureless brown area with irregular dots and asymmetrically pigmented follicular openings are present.FIGURE 2.: A, Ulcerated tumor composed by irregular columns of well-differentiated atypical keratinocytes and atypical melanocytes arranged in single units and irregular nests (HE, 20x); (B) melanocytes stained positive for Melan-A (20x); (C) keratinocytes resulted positive for pancytokeratin (20x); (D) higher magnification of the well differentiated atypical keratinocytes and the atypical melanocytes (HE, 400x); (E) the 2 cell populations of atypical keratinocytes and melanocytes are strictly combined (HE, 400x); (F) atypical melanocytes arranged in single units and irregular nests in all layers of the epidermis. In the dermis, sparse lymphocytic infiltrate and melanophages (HE, 100x).The occurrence of squamous cell carcinoma and melanoma in the same tumor (SMT) is a rare event; Zaballos et al2 recently found that the most frequent collision tumors (CTs) are: basal cell carcinoma–seborrheic keratosis (37.9%), basal cell carcinoma–melanocytic nevus (19.9%), and melanoma–seborrheic keratosis (6.8%). Histologically, CTs may result from a variety of modality of “collisions” such as colonization, combined, biphasic, biphenotypic, or intermingled neoplasms.3,4 As the case reported by Zipperer et al,1 our case also could be classified as combined SMT. Dermoscopic diagnosis of CT is difficult for experts too.5 Reflectance confocal microscope can be highly useful in the diagnosis.6 To our knowledge, dermoscopic features of SMT have been reported only once by Haenssle et al7 who described an SMT of the nail unit characterized by diffuse gray–brown pigmentation, keratin cysts, multiple brown dots, and a fibrillar pattern combined with dotted/short linear vessels. Besides melanoma, dermoscopic differential diagnosis of SMT is pigmented squamous cell carcinoma that may present radial streaks in the periphery and irregular scal-like hypopigmented area in the center of the lesion with also brownish and reddish globules.8 In conclusion, SMT represent a clinical diagnostic challenge; suspicious lesions should be observed accurately with dermoscopy and promptly excised if malignancy cannot be excluded.