The following is a summary of “Whole-Exome Sequencing of a Case of Squamoid Eccrine Ductal Carcinoma Reveal Similarities With Cutaneous Squamous Cell Carcinoma” published in the July 2023 issue of Dermatopathology by Grube et al.
Squamoid eccrine ductal carcinoma (SEDC) is a weakly documented and likely underdiagnosed spite of the sweat glands associated with a high risk for local recurrence, the possibility of metastasis, and rare disease-related mortality. Histopathologically, the tumor displays a biphasic differentiation pattern: superficially, the tumor demonstrates squamous differentiation [indistinguishable from well-differentiated cutaneous squamous cell carcinoma (cSCC)], whereas the deeper portion shows an infiltrative way with prominent ductal differentiation.
SEDC is diagnosed solely through histopathological examination. Its pathogenesis needs to be more adequately understood, and its genomic characteristics still need to be discovered. In this article, the genomic features of a case of SEDC are characterized using whole-exome sequencing and compared to those of cSCC and other eccrine duct carcinomas. Exome sequencing revealed 30 mutations per megabase, with 21 pathogenic or likely pathogenic mutations identified in 14 genes. The genomic abnormalities identified in this case of SEDC significantly overlap with those of cSCC but not those of other malignant sweat gland tumors.
The previously documented clinical and histopathologic characteristics of SEDC and the genetic aspects of this case suggest that this tumor may arise initially as a well-differentiated cSCC that subsequently undergoes divergent focal differentiation to resemble a malignant sweat gland tumor. To elucidate this consideration, genetic analysis of additional cases is necessary.
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