Benign ve malign melanositik proliferasyonlarda epigenetik değişiklik belirteçleri 5-hidroksi metil sitozin ve histon deasetilaz-6'nın tanısal değeri ve histopatolojik prognostik parametrelerle ilişkisi

ASLIHAN YAVAŞ

Benign ve malign melanositik proliferasyonlarda epigenetik değişiklik belirteçleri 5-hidroksi metil sitozin ve histon deasetilaz-6'nın tanısal değeri ve histopatolojik prognostik parametrelerle ilişkisi

Thesis Type: Expertise In Medicine

Institution Of The Thesis: Ankara University, Tıp Fakültesi, Cerrahi Tıp Bilimleri Bölümü, Turkey

Approval Date: 2018

Thesis Language: Turkish

Student: ASLIHAN YAVAŞ

Supervisor: AYLİN HEPER

Open Archive Collection: AVESIS Open Access Collection

Abstract:

Aim: Melanocytic skin tumors show a broad spectrum including benign and malignant neoplasms with a wide variety of clinical, histopathological and genetic features. Interpretation of melanocytic lesions is one of the most common difficulties in dermatopathology. Malignant melanoma is the most aggressive form of skin cancer which shows high metastatic capacity, rapid progression and high mortality. There is lack of a reliable biomarker which can be useful in the differential diagnosis of malignant melanocytic lesions which is almost the most aggressive form of skin cancer and benign ones and also can be useful in predicting the biological behavior of these lesions. In addition to genetic events, epigenetic mechanisms also play a role in the development and progress of melanoma. Abnormal DNA methylation, formed by the methylation of the cytosine in position 5, an important epigenetic change for various pathological and biological processes, is a mechanism that has been recently elaborated on. Another epigenetic mechanism involved in the regulation of chromatin structure is histone modification. Histone deacetylases (HDAC) and histone acetyltransferases (HAT) play a role in the epigenetic regulation of gene expression in many diseases. The aim of this study is, to investigate the diagnostic utility of epigenetic markers, 5-hmC and HDAC6 in distinguishing malignant, borderline and benign melanocytic lesions; to analyze the relationship between these epigenetic markers and histopathological prognostic parameters in primary melanoma; and to compare the role of these epigenetic changes in tumor progression by comparing them between primary and metastatic melanomas. Material and method: 110 benign (22 dermal nevus, 22 congenital nevi, 22 dysplastic nevi, 22 Spitz nevi, 22 blue nevi), 110 primary malign melanoma (24 nodular melanomas, 24 superficial spreading melanomas, 22 acral lentiginous melanomas, 22 lentiginous maligna melanomas, 18 special types of melanomas [spitzoid, nevoid, desmoplastic, spindle cell]), 8 borderline melanocytic lesions and 100 melanoma metastases (30 skin, 30 soft tissue, 30 lymph nodes and 10 visceral metastases) were included in the study, and a group of 24 patients with both primary lesions and metastatic lesions were included in the study, independently of the subtypes. Besides age and sex of the patients, localisation of the lesions were noted; H-E stained sections of the cases were reexamined and histopathological parameters were evaluated. Histopathological parameters were Breslow tumor thickness, Clark level, number of mitosis per mm2, presence or absence of ulceration, regression, lymphovascular invasion and perineural invasion, presence and density of tumor infiltrating lymphocytes (TIL) in primary malignant melanoma cases; degree of atypia in dysplastic nevi and number of mitosis for whole lesion in both dysplastic nevi, Spitz nevi and borderline lesions. In immunohistochemical analyzes, anti-HDAC6 antibody could be applied to all cases, but due to technical reasons anti-5-hMC antibody could be applied to the 214 cases; evaluations were made on digital images by digitally scanned slides with the H-score which includes the percentage and density of staining. The analysis of the data was made using the "SPSS version 20" package program and the results for p <0.05 were considered to be statistically significant. Results: The mean age of all cases is 49.4 years (6-92). 52.1% (n: 171) of the cases were female and 47.9% (n: 157) were male. The mean age of the primary malignant and metastatic diagnosis groups was higher than the borderline and benign diagnostic groups (p <0.05). The youngest average age was found in Spitz nevus cases, which were statistically significantly lower than dermal, dysplastic and blue nevus cases (p <0.05). Dysplastic and congenital nevi were located preferentially on trunk; blue nevi were found on extremities and lentigo malignant melanomas were on head and neck region. The most common metastized lymph node region was inguinal lymph nodes in the lymph node metastasis group and lung metastasis was the most frequent among visceral metastasis group. Among histopathologic prognostic parameters; nodular melanomas were found to have higher Breslow tumor thickness than other types of melanomas except acral lentiginous melanoma (p <0.05). It was found that nodular melanomas have more mitosis than all of the superficial spreading melanomas, lentigo malignant melanomas and special type melanomas (p<0.05). There was a positive correlation between degree of atypia and mitosis in dysplastic nevi (p<0.05, r:0.497). Lymphovascular invasion was more frequent in nodular (20.8%) and acral lentiginous melanomas (13.6%), whereas there was no difference between primary melanoma subtypes according to perineural invasion. Ulceration was present more frequent in nodular (58.3%) and acral lentiginous melanomas (36.4%). Regression was found highest in superficial spreading melanoma (16.7%). There was no statistically significant difference between primary melanoma subtypes according to TILs. In epigenetic marker analysis, benign lesions showed more and intense 5-hmC expression, while partial or total loss was found in primary malignant and metastatic melanomas. Dermal nevi showed more 5-hmC expression than dysplastic and congenital nevi; congenital nevi exhibited 5-hmC expression similar to dysplastic nevi. Dermal, dysplastic and congenital nevi had higher 5-hmC H-scores than primary melanoma and metastatic melanoma cases. There was no difference between primary malignant and metastatic cases and also between their subdiagnostic groups according to 5-hmC expression. In primary melanoma cases, H-scores of 5- hmC was correlated negatively with Breslow thickness, Clark level, mitosis and was correlated positively with TIL. In primary melanoma, benign melanocytic proliferation and borderline lesion groups, the HDAC6 H-score was not found to be related with any prognostic parameter statistically. Higher HDAC6 expression was higher in metastatic lesions in the group in which the primary and metastases were from the same patient; but 5-hmC showed no difference. Conclusion: The results of our study, suggesting that dysregulation of 5-hmC may be occurring early in the pathogenesis of melanoma and 5-hMC may be a diagnostic and prognostic valuable marker in melanocytic lesions. In terms of similar expression profile of 5-hmC in congenital nevi to dysplastic nevi emphasizes the biological differences of congenital nevi from other benign melanocytic lesions. This is the first study which investigates HDAC6 expression in paraffin-embedded human tissues in a wide range of melanocytic lesions by immunohistochemical method. The results of the group which includes primary and metastatic lesions of same patients suggested that HDAC6 has promoting effects on melanoma metastasis and also therapeutic agents targeting HDAC6 may be beneficial in the treatment of melanoma. However, it would be beneficial to support these results in different and large patient series. Key words: melanocytic lesions, prognostik histopathological parameters, epigenetic markers, 5-hydroxy methyl cytosine (5-hmC), hyston deacetylase-6 (HDAC6)