A Rare Case of a Cutaneous Squamomelanocytic Tumor: Revisiting the Histogenesis of Combined Neoplasms

Abstract

We describe what we believe to be the seventh report of a combined tumor with histologic features of both malignant melanoma and a squamous cell carcinoma, a squamomelanocytic tumor. An 82-year-old woman presented with a nondescript, skin-colored, firm papule on her nose. Histology showed 2 different neoplastic cell proliferations: atypical squamoid cells and irregularly shaped nests of atypical pigmented epithelioid cells (melanocytes) arranged in small to large nests at the dermal-epidermal junction and within the epidermis. Both components were closely admixed and restricted to the epidermis. Immunohistochemistry showed diffuse cytoplasmic reactivity for pancytokeratin in all areas supporting the histopathologic features of a squamous cell carcinoma. S-100 and melanoma antigen recognized by T cells 1 did not stain these areas and showed strong selective positivity for the atypical melanocytic component. A true malignant proliferation of 2 distinct cell phenotypes due to close paracrine interactions is our favored interpretation because of the intimate admixture, distinct immunohistochemical pattern, and unique histologic features. Perhaps, chronic sun damage (facial location and advanced age) and reduced immunity (history of other malignancies, particularly recent history of a basal cell carcinoma) played a complementary role for the development of the squamomelanocytic tumor.

Combined cutaneous tumors with a melanoma component: A clinical, histologic, and molecular study

“…In the cases published, follow-up time ranged from 6 months to 9 years, with an average of approximately 15 months. 1,4,6,21,23,26,27 Despite reports of Breslow depths ranging from 1.0 to 6.0 mm, 1,23,28 to our knowledge, only 1 previously published case has resulted in death directly from the CCT: a patient diagnosed with a BMT having a Breslow depth of 3.0 mm. 11 Five cases with a median Breslow depth of 4.2 mm (range, 1.4-6 mm) have had local tumor recurrence and/or regional metastases.…”

“…Field cancerization theory proposes that exposure to a common carcinogenic factor, such as ultraviolet radiation, within a field area facilitates proliferation of neoplastic cells and the development of 2 different tumors within 1 lesion. 4,23 SCCs, BCCs, and melanomas are all more likely to occur on chronically sun-damaged skin, and [80% of our cases had extensive solar elastosis. In addition, most of our cases arose from the head and neck region of older men.…”

“…4,[19][20][21][22] Many terms have been used to describe these tumors, reflecting the various theories behind their histogenesis. 4,5,18,23 Because of differing terminologies, it is difficult to ascertain how many cases have been reported. Based on our review of the English literature, we estimate that fewer than 50 cases of SMTs, BMTs, and trichoblastomelanomas have been described.…”

Squamomelanocytic Tumor of the Nail Unit Metastasizing to a Sentinel Lymph Node: A Dermoscopic and Histologic Investigation

“…Since the publication of a first case series in 1999 [1] only 9 more cases have been reported in the world literature [2,3,4,5,6,7,8,9]. The large majority of earlier cases (11 out of 12) involved chronically sun-exposed skin of the face and scalp area.…”

“…To our knowledge, among the 13 cases in the world literature [1,2,3,4,5,6,7,8,9], this is the first reported SMT involving the nail unit (table 1). …”