High tumour mutational burden and EGFR/MAPK pathway activation are therapeutic targets in metastatic porocarcinoma

BACKGROUND

Eccrine porocarcinoma (EPC) is a rare skin cancer arising from the eccrine sweat glands. Due to the lack of effective therapies, metastasis is associated with a high mortality rate.

OBJECTIVES

To investigate the drivers of EPC progression.

METHODS

We carried out genomic and transcriptomic profiling of metastatic EPC (mEPC), validation of the observed alterations in an EPC patient-derived cell line, confirmation of relevant observations in a large patient cohort of 30 tumour tissues, and successful treatment of a patient with mEPC under the identified treatment regimens.

RESULTS

mEPC was characterized by a high tumour mutational burden (TMB) with an ultraviolet signature, widespread copy number alterations and gene expression changes that affected cancer-relevant cellular processes such as cell cycle regulation and proliferation, including a pathogenic TP53 (tumour protein 53) mutation, a copy number deletion in the CDKN2A (cyclin dependent kinase inhibitor 2A) region and a CTNND1/PAK1 [catenin delta 1/p21 (RAC1) activated kinase 1] gene fusion. The overexpression of EGFR (epidermal growth factor receptor), PAK1 and MAP2K1 (mitogen-activated protein kinase kinase 1; also known as MEK1) genes translated into strong protein expression and respective pathway activation in the tumour tissue. Furthermore, a patient-derived cell line was sensitive to EGFR and MEK inhibition, confirming the functional relevance of the pathway activation. Immunohistochemistry analyses in a large patient cohort showed the relevance of the observed changes to the pathogenesis of EPC. Our results indicate that mEPC should respond to immune or kinase inhibitor therapy. Indeed, the advanced disease of our index patient was controlled by EGFR-directed therapy and immune checkpoint inhibition for more than 2 years.

CONCLUSIONS

Molecular profiling demonstrated high TMB and EGFR/MAPK pathway activation to be novel therapeutic targets in mEPC.

Facies leontina bei chronischer lymphatischer Leukämie

Wir berichten über die seltene Entwicklung einer Leukaemia cutis, die sich als Facies leontina bei einem Patienten mit seit 4 Jahren bekannter chronischer lymphatischer Leukämie manifestierte. In Zusammenschau der Histomorphologie und des immunhistochemischen Phänotyps zeigte sich in der Dermis ein monomorphes Infiltrat von kleinen lymphatischen Zellen mit runden chromatindichten Zellkernen sowie Koexpression von CD20, CD5 und CD23. Dazwischen eingestreut waren einzelne CD3-positive T-Zellen. Obwohl die Facies leontina am häufigsten mit der lepromatösen Lepra oder einem kutanen T-Zell-Lymphom assoziiert ist, sollte insbesondere bei älteren Menschen auch an eine zugrundeliegende Leukämie gedacht werden.