LEF-1 expression in basal cell carcinomas

Segmental basaloid follicular hamartomas derive from a post-zygotic SMO p.L412F pathogenic variant and express hair follicle development-related proteins in a pattern that distinguish them from basal cell carcinomas

Basaloid follicular hamartomas (BFH) are benign small basaloid skin tumors that can present as solitary or multiple lesions. Congenital BFH lesions arranged in a segmental distribution have been described, suggesting they derive from a somatic post-zygotic mutational event. Previously, BFH were described in Happle-Tinschert syndrome, which results from a post-zygotic SMO variant and is characterized by segmental BFH with variable involvement of the teeth, skeleton, and central nervous system. Here, we describe two patients with isolated segmental BFH and no systemic involvement. Paired whole exome sequencing of BFH and normal tissue revealed a pathogenic SMO c.1234 C>T, p.L412F variant restricted to BFH tissue. We characterized the proliferation index and expression of Hedgehog and Wnt/beta-catenin pathway related proteins in segmental BFH compared to sporadic basal cell carcinomas (BCCs) and found that segmental BFH had a lower proliferation index. Although segmental BFH expressed a similar level of Gli-1 compared to BCCs, levels of LEF-1 and SOX-9 expression in BFH were weaker for both and patchier for LEF-1. Our results show that a somatic SMO activating variant causes segmental BFH. Since these patients are prone to developing BCCs, differences in SOX9, LEF1, and Ki-67 expression can help distinguish between these two basaloid lesions.

Merkel cell carcinoma in the setting of hematologic disease is associated with unique features and potential pitfalls

Merkel cell carcinoma (MCC) is a rare but aggressive neuroendocrine carcinoma of the skin, often associated with polyomavirus and ultra-violet light exposure. Immunosuppression is associated with increased risk of development of MCC, including that associated with hematolymphoid disorders such as chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL). We sought to determine whether MCC arising in patients with hematologic disorders showed unique features. Searching archived material at three institutions, we identified 13 patients with MCC and at least one hematologic malignancy and 41 patients with MCC with no reported hematologic malignancy. CLL/SLL was the most common hematologic disorder in this setting (9/13 cases). Clinical history, variation in morphologic appearance, unusual site distribution and concern for progression of underlying hematologic disease all contributed to potential diagnostic challenges. Overlapping marker expression between MCC and hematologic neoplasms created potential diagnostic pitfalls (e.g. CD138, Pax5, TdT, Bcl2, CD56, and CD117). In addition, we newly identify expression of CD5 and LEF-1 in a subset of MCC, including in patients with CLL/SLL. MCC in patients with hematologic malignancy were more common in men (92% versus 59%, p < 0.05) and showed an unusual site predilection to non-sun exposed sites (3/13 on the buttocks) with none presenting on the face or scalp. By contrast, face or scalp lesions were common in MCC without an associated hematologic malignancy (17/41, p < 0.05). Our findings reaffirm the need for skin surveillance in the setting of immune deficiency and for vigilance to identify unusual presentations of MCC in patients with or without hematologic disorders.

Magnifying glass on spiradenoma and cylindroma histogenesis and tumorigenesis using systematic transcriptome analysis

Spiradenoma and cylindroma are related sweat gland tumors. To delineate their histogenesis, gene profiles, and their potential drivers, we performed a whole-transcriptome sequencing analysis of fourteen samples of spiradenoma/cylindroma in comparison to normal samples. A total of 12 spiradenomas, 5 cylindromas, 3 hybrid spiradenomas/cylindromas and 2 adnexal carcinomas were included in this study. 1335 characteristic genes and transcripts expressed over all 14 spiradenoma/cylindroma tumors were identified, and two groups of expression profiles were observed. Highest upregulated top 7 gene signatures characterized benign tumors with developmental and differentiation related genes, and carcinomas with top 7 genes mainly related to signaling, reorganization and metabolism of membranes. Immunohistochemistry of protein expressions validated 4 upregulated genes (ODAM, HOXB13, MYB and SOX10) considered important and as potential biomarkers for spiradenomas and cylindromas. We further compared the transcriptome of eccrine adnexal tumors with the transcriptome of adenoid cystic carcinoma (ACC) to identify the overlapping genes that may indicate histogenesis. There were 36 specific genes overlapping between adnexal carcinomas and the epithelial-dominant subtype of ACC, and 27 specific genes overlapping benign adnexal tumors with the myoepithelial-dominant subtype of ACC, At this point there is no known specific biomarker to aid in the diagnosis of eccrine spiradenoma and cylindroma in small samples or biopsies within the context of morphological overlap with ACC. In conclusion, spiradenomas and cylindromas are characterized by overexpressed developmental genes, where LHX2 and activated WNT signaling possibly drive associated carcinomas.

LEF-1: Diagnostic utility in distinguishing basaloid neoplasms of the salivary gland

BACKGROUND

Lymphoid enhancer binding factor 1 (LEF-1) has recently been reported as a potential immunohistochemical (IHC) marker for basal cell adenoma (BCA) and other salivary gland tumors, which may contribute to an increased accuracy in differentiating basaloid salivary gland neoplasms. We evaluated the utility of LEF-1 in fine needle aspiration (FNA) and resection specimens to distinguish pleomorphic adenoma (PA), BCA, basal cell adenocarcinoma (BCAC), and adenoid cystic carcinoma (ACC) as well as in non-neoplastic salivary gland (NNSG).

METHODS

Cases including 66 PA (35 FNA, 31 resections), 12 BCA (5 FNA, 7 resections), 42 ACC (11 FNA, 31 resections), 1 BCAC FNA, and 10 NNSG (5 FNA, 5 resections) were obtained and stained for LEF-1.

RESULTS

On cell block (CB), 51% of PA and 60% of BCA were LEF-1 positive while 91% of ACC were LEF-1 negative. Among resections, there was a higher percentage of LEF-1 positive PA (84%) and BCA (86%), and a higher percentage of LEF-1 negative ACC (97%). LEF-1 staining had a low to moderate sensitivity for detecting benign basaloid neoplasms on FNA CB and resection specimens (52.5% and 84%, respectively), but a higher specificity (92% and 97% respectively), and positive predictive value (95% and 97% respectively).

CONCLUSION

When comparing benign (PA and BCA) and the most common malignant basaloid salivary gland tumor (ACC), positive LEF-1 favors a benign neoplasm. Additional studies with LEF-1, specifically including other rare basaloid salivary gland neoplasms are needed to further clarify the role of LEF-1 in diagnosing these lesions on FNA.

Dysregulated TRK signalling is a therapeutic target in CYLD defective tumours

Individuals with germline mutations in the tumour suppressor gene CYLD are at high risk of developing disfiguring cutaneous appendageal tumours, the defining tumour being the highly organised cylindroma. Here, we analysed CYLD mutant tumour genomes by array comparative genomic hybridisation (aCGH) and gene expression microarray analysis. CYLD mutant tumours were characterised by an absence of copy number aberrations apart from loss-of-heterozygosity at chromosome 16q, the genomic location of the CYLD gene. Gene expression profiling of CYLD mutant tumours revealed dysregulated tropomyosin kinase (TRK) signalling with overexpression of TRKB and TRKC in tumours when compared to perilesional skin. Immunohistochemical analysis of a tumour microarray demonstrated strong membranous TRKB and TRKC staining in cylindromas, as well as elevated levels of ERK phosphorylation and BCL2 expression. Membranous TRKC overexpression was also observed in 70% of sporadic basal cell carcinomas. RNA interference mediated silencing of TRKB and TRKC, as well as treatment with the small molecule TRK inhibitor lestaurtinib, reduced colony formation and proliferation in three-dimensional primary cell cultures established from CYLD mutant tumours. These results suggest that TRK inhibition could be used as a strategy to treat tumours with loss of functional CYLD.