An Atypical Deep Penetrating Nevus With Mutations in Beta Catenin , BRAFV600E , and IDH1R132C in an 8-Year-Old Boy.

ABSTRACT: Deep penetrating nevus (DPN) is a pigmented melanocytic tumor which typically displays a wedge-shaped deep penetrating architecture. Some cases show a coexisting component resembling conventional melanocytic nevus. These morphological attributes are correlated with the acquisition of genomic alterations in the Wnt pathway on a background of underlying activating MAPK pathway mutations. Lesions with features of DPN, but displaying expansile architecture, sheet-like arrangement of cells, cytological atypia, and/or more than rare mitotic activity have been described as "atypical deep penetrating nevus" or "deep penetrating melanocytoma." The molecular correlates of these atypical morphological features are not well-established. In this case report, we describe a tumor in an 8-year-old boy with histological features of atypical DPN showing somatic BRAFV600E , beta catenin , and IDH1R132C mutations. The combination of abnormalities in MAPK and Wnt pathways with IDH1 mutations seems to be a reproducible feature in a subset of atypical DPNs. Whether this "three-hit" combination is associated with a significant risk of adverse outcome remains to be established.

Merkel Cell Carcinosarcoma With a Bland Sarcomatous Component.

ABSTRACT: Merkel cell carcinoma with a sarcomatous component is very rare, with only 12 cases reported in the literature, often with overtly malignant myoid differentiation. We report a case of metastatic Merkel cell carcinosarcoma presenting in a lymph node 6 months after a diagnosis of cutaneous Merkel cell carcinoma with conventional histologic features. The metastatic lesion showed a unique biphasic appearance with admixed populations of neuroendocrine epithelial cells and fascicles of mitotically active spindle cells with mild cytological atypia. In addition to the immunomorphological features, a common molecular profile between the epithelial and mesenchymal components further supported the notion of carcinosarcoma in this case. To the best of our knowledge, a bland sarcomatous component has not been previously described in Merkel cell carcinosarcoma, which can be easily overlooked as a reactive stromal reaction microscopically.

Paediatric cutaneous adnexal tumours: a study of 559 cases.

Cutaneous adnexal tumours encompass a wide group of lesions with apocrine, eccrine, follicular, sebaceous and mixed differentiation. The large majority are benign and represent sporadic lesions, though malignant forms are occasionally encountered and some cases develop in the setting of inherited tumour syndromes. Accurate histological classification can be difficult as there are numerous histological appearances, many of which are individually uncommon, and complex, overlapping and historically variable nomenclature is typical. The aim of this study was to review and classify the spectrum of cutaneous adnexal tumours seen in patients 18 years of age and under in two major tertiary centres over a 20 year period. A total of 559 cases were included, with 60% occurring in female patients. The large majority (87%) occurred in the head and neck region and were benign. Only one (0.2%) was malignant. The original diagnosis was supported by histological review in 99% of cases of pilomatricoma reviewed, but in only 71% of non-pilomatricoma cases reviewed. The most common lineage was follicular (97%), with pilomatricoma accounting for the large majority of lesions. Predominant glandular/ductal differentiation was seen in 3% of cases, with no tumours showing predominant sebaceous differentiation.