Adnexal tumors of the skin comprise heterogenous group with over 40 defined entities, classified by predominant differentiation into lesions with apocrine and eccrine, follicular, sebaceous, or multilineage differentiation. Some, but not all these entities are represented by benign and malignant counterparts. Their occurrence may be sporadic or as a part of inherited syndromes (e.g. Muir-Torre syndrome, Brooke-Spiegler Syndrome, or Cowden’s syndrome). Adnexal tumors may arise de novo or within hamartomatous lesions such as nevus sebaceous of Jadassohn. Adnexal carcinomas are very rare tumors (the incidence is less than 0.001%), with variable local recurrence, metastatic potential, and survival. Porocarcinoma, hidradenocarcinoma and sebaceous carcinoma (especially ocular type) are considered to have a poor prognosis, with the highest risk of local recurrence and distant metastases. Mortality of the patients with porocarcinoma is very high (65-80%) if regional or distant metastases are present. The treatment of malignant adnexal tumors is usually surgical or less frequently with radiation therapy. Patients with metastases are usually treated with chemotherapy, mostly with cytotoxic reagents, and rarely with estrogen receptor antagonists. The detailed knowledge of genetic features of adnexal tumors is still lacking. Most of the studies examined only few of the genes using low throughput techniques. Development of new generations of genome sequencing methods led to better understanding of tumors with apocrine and eccrine differentiation. For many of their subtypes, it is still unknown whether there are specific genetic changes, that could even be of diagnostic significance. Hotspot mutations in HRAS (p.G13X and p.Q61X) were found in a subset of eccrine poromas and porocarcinomas. These mutations were found in tumors with other lines of differentiation and suggesting overlapping genetical characteristics among adnexal tumors. Due to their similar histological features, cylindroma and spiradenoma are usually considered as phenotypic variations of the same entity. Their histological features can be mixed, in which case a diagnosis of spiradenocylindroma is made. In cylindroma, MYB is upregulated either by mutations in CYLD gene (syndromic cases) or due to a rearrangement of MYB gene (sporadic cases). Genetic characteristics of spiradenomas, including the status of CYLD and MYB genes, are largely unknown. It is still unclear if these two are both histological and genetical “relatives” and what is the level of heterogeneity among tumors arising sporadically or within syndromes. The presence of chromosomal rearrangements in adnexal tumors is also unexplored. TORC1-MAML2 and EWSR1-POU5F1 fusions were found in significant number of hidradenomas. Initially it was thought these fusions could be characteristic for clear cell variant of hidradenomas, but no true correlation with histology was found. Molecular alterations that differ between benign and malignant counterparts and could enable targeted therapy of adnexal carcinomas are unknown. Mutations in TP53, often UV-associated, are frequent in malignant tumors with eccrine and apocrine differentiation and can drive malignant transformation in such tumors. Porocarcinomas and ABSTRACTS 96 MATERIA MEDICA • Vol. 34 • Issue 1, suplement 1 • april 2018. hidradenocarcinomas harbor various molecular alterations affecting PI3K-AKT or MAPK pathways that could enable targeted therapy in the future. Actionable mutations in EGFR were not found in carcinomas with eccrine and apocrine differentiation thus far. Her2 amplifications are rarely found, mostly in hidradenocarcinomas, but its therapeutic potential has only been utilized only once.16,25 Mutations of PTCH1 and TCF7L1 in hidradenocarcinomas could also enable the treatment with the inhibitors of Hedgehog and WNT/Hippo signaling pathways. It seems that current knowledge gained from genomic studies of adnexal tumors is only a scratch on the surface. In addition, there is no data on epigenetic characteristics or transcriptome of adnexal skin tumors. Taken altogether, further and detailed investigation of genome, epigenome and transcriptome of adnexal tumors is necessary. Such integrated knowledge could explain mechanisms of their development, malignant alteration and progression, so the treatment of patients with metastatic adnexal carcinomas could be changed toward targeted therapy.

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