Microsurgical Endoscope-Assisted Gravity-Aided Transfalcine Approach for Contralateral Metastatic Deep Medial Cortical Tumors

BACKGROUND

Traditional approaches to deep medial cortical tumors utilize transcortical or ipislateral interhemispheric approaches, which can result in cortical damage or retraction injury. To reduce these risks, the microscopic transfalcine approach has been previously described.

OBJECTIVE

To describe this approach performed with endoscopic assistance for metastatic tumor resection, demonstrating appropriate and safe tumor resection without injury to the contralateral hemisphere.

METHODS

Eleven consecutive patients harboring medial, deep metastatic tumors are reported. Tumor resection was performed with endoscopic assistance with 2 surgeons. Clinical outcomes are recorded.

RESULTS

All 11 patients underwent safe tumor resection. Gross total resection was achieved in 73% of patients. The application of the angled endoscope allowed for further tumor resection in 91% of patients. There were no complications in these patients. The contralateral brain did not demonstrate clinical or radiographic injury as well.

CONCLUSION

This series suggests that the endoscopic transfalcine approach in the lateral position can be a safe and effective approach for resecting medial interhemispheric metastatic tumors. It allows excellent tumor visualization, eliminates the need for brain retraction, minimizes parenchymal transgression, and improves surgical ergonomics. A familiarity of endoscopy and neuroanesthesia support is helpful when utilizing this approach.

Abstract P1-04-04: DNA methylation landscapes of breast cancer progression to brain metastasis: A pre-clinical study

Due to improvements in overall survival rates, breast cancer brain metastasis (BCBM) is a major life-limiting condition with rising incidence. The molecular mechanisms involved in breast cancer (BC) progression to brain metastasis are still poorly understood. We have demonstrated that DNA methylation, a key epigenetic regulatory mechanism, is involved in BC progression to metastatic disease. Here, we characterized the BCBM DNA methylation landscapes according to their molecular subtypes. Methods: This study included 22 BCBM specimens from 19 patients (ER+/PgR+/HER2-(n=6), HER2+(n=7), and ER-/PgR-/HER2-(TNBC; n=6)) and primary BC specimens with paired molecular subtypes. After microdissection, we generated genome-wide DNA methylomes using HM450K BeadChips. Results: Multidimensional scaling revealed that DNA methylation patterns specifically clustered BCBMs according to their respective molecular subtypes. Additionally, we observed that while ER+/PgR+/HER2- BCBM showed a significant global hypermethylation, HER2+ and TNBC BCBMs presented a significant global hypomethylation compared to the respective primary BC specimens. Hypermethylation on ER+/PgR+/HER2- BCBMs mainly affected CpG islands and was significantly enriched in regions overlapping tumor-related genes, such as APC2, CREB3L1, and GLI3; and a large number of developmental genes, including HOXA9, HOXA10, HOXB13, and PAX6 (Table1). On the other hand, hypomethylation on HER2+ and TNBC BCBMs significantly overlapped with conserved intergenic cis regulatory elements. Two significantly affected regions included enhancer elements associated with NEUROD1, a neurogenic differentiation factor, and MYT1L, a Pan-neural transcription factor associated with neuronal differentiation, suggesting an acquisition of brain-like properties (Table2). Conclusions: Our study suggests a significant role of DNA methylation reprogramming during BC progression to brain metastasis and describes the existence of molecular subtype-specific DNA methylomes. Altogether, this data offers new insight into the complexity of this clinical complication.

Table1: Hypermethylated CpG sites in ER+/PgR+/HER2- BCBMChrStartGeneCpG ContextDiff. MethFDR P-val1746802888HOXB13Island0.824.6E-061656666575MT1MIsland0.813.7E-101685160569IntergenicShelf0.773.7E-17742277807GLI3Island0.738.7E-0567728888BMP6Island0.713.1E-051811149470FAM38BIsland0.703.4E-081146317577CREB3L1Shore0.705.3E-17191467979APC2Island0.693.0E-05727213984HOXA10Island0.697.5E-061131826421PAX6Island0.677.4E-06727205381HOXA9Island0.651.7E-061396204854CLDN10Island0.642.1E-042176956678HOXD13Island0.632.3E-04

Table2: Hypomethylated CpG sites in HER2+ and TNBC BCBMsChrStartGeneCpG ContextDiff. Meth.FDR P-val1746619555IntergenicShore-0.583.2E-042182543233NEUROD1OpenSea-0.566.9E-0312132900938GALNT9Island-0.562.1E-051391827042IntergenicShore-0.558.7E-051746618614IntergenicShore-0.551.4E-0522119853MYT1LOpenSea-0.532.5E-041156623074BCANOpenSea-0.532.1E-0310128275008IntergenicOpenSea-0.521.6E-04480885981ANTXR2Island-0.515.2E-037157280331IntergenicShelf-0.516.9E-032059832924CDH4Shelf-0.512.7E-0241407858IntergenicIsland-0.513.7E-03592925721NR2F1Shore-0.513.1E-08

Citation Format: Orozco JIJ, Bustos MA, Nelson N, Hsu SC, Cheung G, Bostick PJ, Lucci A, DiNome M, Kelly DF, Hoon DSB, Marzese DM. DNA methylation landscapes of breast cancer progression to brain metastasis: A pre-clinical study [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P1-04-04.

AMERICAN ASSOCIATION OF CLINICAL ENDOCRINOLOGISTS AND AMERICAN COLLEGE OF ENDOCRINOLOGY DISEASE STATE CLINICAL REVIEW: A NEUROENDOCRINE APPROACH TO PATIENTS WITH TRAUMATIC BRAIN INJURY

OBJECTIVE

Traumatic brain injury (TBI) is now recognized as a major public health concern in the United States and is associated with substantial morbidity and mortality in both children and adults. Several lines of evidence indicate that TBI-induced hypopituitarism is not infrequent in TBI survivors and may contribute to the burden of illness in this population. The goal of this article is to review the published data and propose an approach for the neuroendocrine evaluation and management of these patients.

METHODS

To identify pertinent articles, electronic literature searches were conducted using the following keywords: "traumatic brain injury," "pituitary," "hypopituitarism," "growth hormone deficiency," "hypogonadism," "hypoadrenalism," and "hypothyroidism." Relevant articles were identified and considered for inclusion in the present article.

RESULTS

TBI-induced hypopituitarism appears to be more common in patients with severe TBI. However, patients with mild TBI or those with repeated, sports-, or blast-related TBI are also at risk for hypopituitarism. Deficiencies of growth hormone and gonadotropins appear to be most common and have been associated with increased morbidity in this population. A systematic approach is advised in order to establish the presence of pituitary hormone deficiencies and implement appropriate replacement therapies.

CONCLUSION

The presence of traumatic hypopituitarism should be considered during the acute phase as well as during the rehabilitation phase of patients with TBI. All patients with moderate to severe TBI require evaluation of pituitary function. In addition, symptomatic patients with mild TBI and impaired quality of life are at risk for hypopituitarism and should be offered neuroendocrine testing.

Proteomics Analysis of Brain Meningiomas in Pursuit of Novel Biomarkers of the Aggressive Behavior

The aim of this pilot study was to evaluate the use of advanced proteomics techniques to identify novel protein markers that contribute to the transformation of benign meningiomas to more aggressive and malignant subtypes. Multiplex peptide stable isotope dimethyl labelling and nano-LCMS was used to identify and quantify the differentially expressed proteins in WHO Grade I, II and III meningioma tissues. The proteins identified will help elucidate the process of transformation to malignancy and may contribute to improved diagnosis and treatment of these aggressive tumors.

Epigenomic landscape of melanoma progression to brain metastasis: unexplored therapeutic alternatives

Melanoma brain metastasis is a complication with rising incidence. Despite the high rate of somatic mutations driving the initial stages of melanocyte transformation, the brain colonization requires a phenotypic reprogramming that is, in part, influenced by epigenomic modifications. This special report summarizes recent findings in the epigenomic landscape of melanoma progression to brain metastasis, with particular emphasis on the clinical utility of DNA methylation, chromatin modifications and ncRNA expression as theragnostic markers, as well as the significance of the metastatic microenvironment on melanoma brain metastasis epigenome.

Endoscopic and Gravity-Assisted Resection of Medial Temporo-occipital Lesions Through a Supracerebellar Transtentorial Approach: Technical Notes With Case Illustrations

BACKGROUND

Traditional approaches to medial temporo-occipital intra-axial brain tumors carry the risk of visual or language deficits related to brain retraction or transgression of deep fiber tracts. To reduce these risks, the microscopic supracerebellar transtentorial approach with the patient in the sitting position has been previously described for lesions in relative proximity to the tentorium.

OBJECTIVE

We describe this approach performed with endoscopic tumor resection to allow better visualization and a more ergonomic operating position.

METHODS

Four consecutive patients harboring a medial temporo-occipital lesion are reported. All were operated on while in the sitting position using frameless navigation and a supracerebellar transtentorial approach. Tumor resection was performed by 2 surgeons with endoscopic visualization.

RESULTS

Pathologies included intraparenchymal metastatic melanoma, cavernous hemangioma, and ganglioglioma, as well as an intraventricular metastatic tumor. The distance from the tentorium to the lesion ranged from 1 to 4 mm. Gross total resection was achieved in 3 of the 4 patients. The patient with a metastatic melanoma had an intentional near-total resection given the tumor encasing a branch of the posterior cerebral artery. The patient with the intraventricular tumor sustained a small but symptomatic infarct of the lateral geniculate region, resulting in a visual field deficit.

CONCLUSION

This small series suggests that the endoscopic supracerebellar transtentorial approach with the patient in the sitting position can be a safe and effective approach for removing medial temporo-occipital lesions. It allows excellent tumor visualization, eliminates the need for brain retraction, minimizes parenchymal transgression, and improves surgical ergonomics. Significant experience in endoscopy and excellent neuroanesthesia support are recommended before undertaking this approach.

Abstract A10: Higher incidence of epigenomic alterations on BRAF and NRAS wild type melanoma brain metastases

Combined BRAF and NRAS gene mutations (mt) account for 70-80% of metastatic melanomas. Patients with BRAFmt benefit from novel targeted therapies; however, patients without this mutation lack effective targeted therapies. We have recently demonstrated that epigenetic alterations are alternative melanoma brain metastasis (MBM) drivers. Here, we propose that identifying epigenome-wide alterations on patients with MBM BRAF and NRAS wild type can identify novel epigenetic drug-based therapies. We performed targeted sequencing to cover the complete exon coverage of mutations of the BRAF and NRAS genes. Firstly, this analysis revealed a mutual exclusivity between BRAFmt and NRASmt. Of the 79% (100/127) of MBMs that carried BRAF or NRAS mutations, 57.5% (73/127) were BRAFmt and 21.2% (27/127) were NRASmt. The remaining 21.2% (27/127) were double wild type (BRAFwt/NRASwt). To identify genome-wide DNA methylation differences between MBMs harboring BRAFmt, NRASmt, or BRAFwt/NRASwt, we generated methylome maps of each MBM type using the Human methylation 450K BeadChip. BRAFwt/NRASwt MBMs presented a significantly higher methylation level (mean = 51% methylation level) than MBMs with NRASmt (mean = 48%) or BRAFmt (mean = 47% methylation level; P<0.001), suggesting a higher influence of epigenetic alterations. 1,598 CpG sites were significantly differentially methylated in BRAFwt/NRASwt MBMs (FDR-corrected P<0.05). Among the most affected genes, we identified significant enrichment on gene networks involved in oncogenic and pro-metastatic functions. These gene networks include apoptosis cascade, adhesion molecules, autophagy regulation, cell cycle regulation, ganglioside metabolism, homeotic and paralog genes (mainly from HOXA gene cluster, PAX6 and PAX7 genes), invasion mechanisms (including multiple metalloproteinase genes), oncogenic growth signaling (including BRAF, PI3K, RAC, and NOTCH pathways, among others), major master transcription factors (including MITF, SOX2, and SOX8), key tumor suppressor genes (including APC, ATM, BRCA1, RB1, and RUNX3, among others), and key epigenome regulatory factors, including DNA methyltransferases (DNMT3B and DNMT3L genes), histone deacetylases (HDAC2, HDAC3, HDAC4, HDAC5 genes) and lysine demethylases (KDM2A, KDM2B, KDM3A, KDM4B, KDM6B genes). Our study suggests the existence of a larger epigenomic alteration influence in double wild type (BRAFwt/NRASwt) MBMs than MBMs with driver mutations on BRAF or NRAS genes and provides the basis for the identification of novel and alternative epigenome-targeted therapies for melanoma patients with MBMs that cannot benefit from current targeted therapies.

Citation Format: Diego M. Marzese, Jamie L. Huynh, Sharon K. Huang, Garni Barkhoudarian, Daniel F. Kelly, and Dave S.B. Hoon. Higher incidence of epigenomic alterations on BRAF and NRAS wild type melanoma brain metastases. [abstract]. In: Proceedings of the AACR Special Conference: Advances in Brain Cancer Research; May 27-30, 2015; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2015;75(23 Suppl):Abstract nr A10.

Impact of selective pituitary gland incision or resection on hormonal function after adenoma or cyst resection

OBJECTIVE

With the resection of pituitary lesions, the anterior pituitary gland often obstructs transsphenoidal access to the lesion. In such cases, a gland incision and/or partial gland resection may be required to obtain adequate exposure. We investigate this technique and determine the associated risk of post-operative hypopituitarism.

METHODS

All patients who underwent surgical resection of a pituitary adenoma or Rathke cleft cyst (RCC) between July 2007 and January 2013 were analyzed for pre- and post-operative hormone function. The cohort of patients with gland incision/resection were compared to a case-matched control cohort of pituitary surgery patients. Total hypophysectomy patients were excluded from outcome analysis.

RESULTS

Of 372 operations over this period, an anterior pituitary gland incision or partial gland resection was performed in 79 cases (21.2 %). These include 53 gland incisions, 12 partial hemi-hypophysectomies and 14 resections of thinned/attenuated anterior gland. Diagnoses included 64 adenomas and 15 RCCs. New permanent hypopituitarism occurred in three patients (3.8 %), including permanent DI (3) and growth hormone deficiency (1). There was no significant difference in the rate of worsening gland dysfunction nor gain of function. Compared to a control cohort, there was a significantly lower incidence of transient DI (1.25 vs. 11.1 %, p = 0.009) but no significant difference in permanent DI (3.8 vs. 4.0 %) in the gland incision group.

CONCLUSION

Selective gland incisions and gland resections were performed in over 20 % of our cases. This technique appears to minimize traction on compressed normal pituitary gland during removal of large lesions and facilitates better visualization and removal of cysts, microadenomas and macroadenomas.

Evolution of minimally invasive approaches to the sella and parasellar region

Introduction Given advancements in endoscopic image quality, instrumentation, surgical navigation, skull base closure techniques, and anatomical understanding, the endonasal endoscopic approach has rapidly evolved into a widely utilized technique for removal of sellar and parasellar tumors. Although pituitary adenomas and Rathke cleft cysts constitute the majority of lesions removed via this route, craniopharyngiomas, clival chordomas, parasellar meningiomas, and other lesions are increasingly removed using this approach. Paralleling the evolution of the endonasal route to the parasellar region, the supraorbital eyebrow craniotomy has also been increasingly used as an alternative minimally invasive approach to reach this skull base region. Similar to the endonasal route, the supraorbital route has been greatly facilitated by advances in endoscopy, along with development of more refined, low-profile instrumentation and surgical navigation technology.

Objectives This review, encompassing both transcranial and transsphenoidal routes, will recount the high points and advances that have made minimally invasive approaches to the sellar region possible, the evolution of these approaches, and their relative indications and technical nuances.

Data Synthesis The literature is reviewed regarding the evolution of surgical approaches to the sellar region beginning with the earliest attempts and emphasizing technological advances, which have allowed the evolution of the modern technique. The surgical techniques for both endoscopic transsphenoidal and supraorbital approaches are described in detail. The relative indications for each approach are highlighted using case illustrations.

Conclusions Although tremendous advances have been made in transitioning toward minimally invasive transcranial and transsphenoidal approaches to the sella, further work remains to be done. Together, the endonasal endoscopic and the supraorbital endoscope-assisted approaches are complementary minimally invasive routes to the parasellar region.

The expanding role of the endonasal endoscopic approach in pituitary and skull base surgery: A 2014 perspective

BACKGROUND

The past two decades have been the setting for remarkable advancement in endonasal endoscopic neurosurgery. Refinements in camera definition, surgical instrumentation, navigation, and surgical technique, including the dual surgeon team, have facilitated purely endonasal endoscopic approaches to the majority of the midline skull base that were previously difficult to access through the transsphenoidal microscopic approach.

METHODS

This review article looks at many of the articles from 2011 to 2014 citing endonasal endoscopic surgery with regard to approaches and reconstructive techniques, pathologies treated and outcomes, and new technologies under consideration.

RESULTS

Refinements in approach and closure techniques have reduced the risk of cerebrospinal fluid leak and infection. This has allowed surgeons to more aggressively treat a variety of pathologies. Four main pathologies with outcomes after treatment were identified for discussion: pituitary adenomas, craniopharyngiomas, anterior skull base meningiomas, and chordomas. Within all four of these tumor types, articles have demonstrated the efficacy, and in certain cases, the advantages over more traditional microscope-based techniques, of the endonasal endoscopic technique.

CONCLUSIONS

The endonasal endoscopic approach is a necessary tool in the modern skull base surgeon's armamentarium. Its efficacy for treatment of a wide variety of skull base pathologies has been repeatedly demonstrated. In the experienced surgeon's hands, this technique may offer the advantage of greater tumor removal with reduced overall complications over traditional craniotomies for select tumor pathologies centered near the midline skull base.

Endonasal Endoscopic Management of Parasellar and Cavernous Sinus Meningiomas

The management of cavernous sinus and invasive parasellar meningiomas often requires a multimodality treatment approach. Early attempts at complete or near-complete removal of parasellar meningiomas involving the cavernous sinus, Meckel cave, clivus, and sella using anterolateral or lateral skull base approaches were typically unsuccessful and yielded high rates of new cranial neuropathy and other complications. This article presents a strategy of endonasal endoscopic parasellar skull base bony decompression and limited tumor removal followed by stereotactic radiotherapy, stereotactic radiosurgery, or observation. Patient selection, technical nuances, potential complications, and initial outcomes in a small series of patients are discussed.

Comparison of sinonasal quality of life and health status in patients undergoing microscopic and endoscopic transsphenoidal surgery for pituitary lesions: a prospective cohort study

OBJECT

Despite the widespread adoption of endoscopic transsphenoidal surgery for pituitary adenomas, the sinonasal quality of life (QOL) and health status in patients who have undergone this technique have not been compared with these findings in patients who have undergone the traditional direct uninostril microsurgical technique. In this study, the authors compared the sinonasal QOL and patient-reported health status after use of these 2 surgical techniques.

METHODS

The study design was a nonblinded prospective cohort study. Adult patients with sellar pathology and planned transsphenoidal surgery were screened at 4 pituitary centers in the US between October 2011 and August 2013. The primary end point of the study was postoperative patient-reported sinonasal QOL as measured by the Anterior Skull Base Nasal Inventory-12 (ASK Nasal-12). Supplementary end points included patient-reported health status estimated by the 8-Item Short Form Health Survey (SF-8) and EuroQol (EQ)-5D-5L instruments, and sinonasal complications. Patients were followed for 6 months after surgery.

RESULTS

A total of 301 patients were screened and 235 were enrolled in the study. Of these, 218 were analyzed (111 microsurgery patients, 107 endoscopic surgery patients). Demographic and tumor characteristics were similar between groups (p ≥ 0.12 for all comparisons). The most common complication in both groups was sinusitis (7% in the microsurgery group, 13% in the endoscopic surgery group; p = 0.15). Patients treated with the endoscopic technique were more likely to have postoperative nasal debridements (p < 0.001). The ASK Nasal-12 and SF-8 scores worsened substantially for both groups at 2 weeks after surgery, but then returned to baseline at 3 months. At 3 months after surgery, patients treated with endoscopy reported statistically better sinonasal QOL compared with patients treated using the microscopic technique (p = 0.02), but there were no significant differences at any of the other postoperative time points.

CONCLUSIONS

This is the first multicenter study to examine the effect of the transsphenoidal surgical technique on sinonasal QOL and health status. The study showed that surgical technique did not significantly impact these patient-reported measures when performed at high-volume centers. Clinical trial registration no.: NCT01504399 ( clinicaltrials.gov ).

The supraorbital endoscopic approach for tumors

OBJECTIVE

To describe the indications, technical nuances, and techniques for complication avoidance for the supraorbital keyhole approach with endoscopic assistance. The supraorbital eyebrow craniotomy provides minimally invasive access to a wide range of frontal fossa, parasellar, and some middle and posterior fossae tumors. This approach is considered ideal for removal of many, if not most, planum and tuberculum sellae meningiomas, some olfactory groove meningiomas, and suprasellar craniopharyngiomas, particularly tumors with far lateral extensions. It is also ideal for many intraaxial tumors, including metastases and gliomas arising from the orbitofrontal, frontal pole, and medial temporal lobe regions. The use of endoscopy further extends the range and versatility of this keyhole approach and is considered an essential adjunct for allowing safe and maximal tumor removal.

Brain metastasis is predetermined in early stages of cutaneous melanoma by CD44v6 expression through epigenetic regulation of the spliceosome

Melanoma brain metastasis (MBM) is frequent and has a very poor prognosis with no current predictive factors or therapeutic molecular targets. Our study unravels the molecular alterations of cell-surface glycoprotein CD44 variants during melanoma progression to MBM. High expression of CD44 splicing variant 6 (CD44v6) in primary melanoma (PRM) and regional lymph node metastases from AJCC Stage IIIC patients significantly predicts MBM development. The expression of CD44v6 also enhances the migration of MBM cells by hyaluronic acid and hepatocyte growth factor exposure. Additionally, CD44v6-positive MBM migration is reduced by blocking with a CD44v6-specific monoclonal antibody or knocking down CD44v6 by siRNA. ESRP1 and ESRP2 splicing factors correlate with CD44v6 expression in PRM, and ESRP1 knockdown significantly decreases CD44v6 expression. However, an epigenetic silencing of ESRP1 is observed in metastatic melanoma, specifically in MBM. In advanced melanomas, CD44v6 expression correlates with PTBP1 and U2AF2 splicing factors, and PTBP1 knockdown significantly decreases CD44v6 expression. Overall, these findings open a new avenue for understanding the high affinity of melanoma to progress to MBM, suggesting CD44v6 as a potential MBM-specific factor with theranostic utility for stratifying patients.

Avoidance of postoperative epistaxis and anosmia in endonasal endoscopic skull base surgery: a technical note

BACKGROUND

Most endoscopic transsphenoidal approaches jeopardize the sphenopalatine artery and septal olfactory strip (SOS), increasing the risk of postoperative anosmia and epistaxis while precluding the ability to raise pedicled nasoseptal flaps (NSF). We describe a bilateral "rescue flap" technique that preserves the mucosa containing the nasal-septal vascular pedicles and the SOS. This approach can reduce the risk of postoperative complications, including epistaxis and anosmia.

METHODS

A retrospective analysis was conducted of all patients who underwent endoscopic transsphenoidal surgery with preservation of both sphenopalatine vascular pedicles and SOS. In a recent subset of patients, olfactory assessment was performed.

RESULTS

Of 174 consecutive operations performed in 161 patients, bilateral preservation of the sphenopalatine vascular pedicle and SOS was achieved in 139 (80 %) operations, including 31 (22 %) with prior transsphenoidal surgery. Of the remaining 35 operations, 18 had a planned formal NSF and 17 had prior surgery or extensive lesions precluding use of this technique. Of pituitary adenomas, RCCs or sellar arachnoid cysts, 118 (94 %) underwent this approach, including 91 % of patients who had prior surgery. Preoperative olfaction function was maintained in 97 % of patients that were tested. None of the patients had postoperative arterial epistaxis.

CONCLUSION

Preservation of bilateral sphenopalatine vascular pedicles and the SOS is feasible in over 90 % of patients undergoing endonasal endoscopic surgery for pituitary adenomas and RCCs. This approach, while not hindering exposure or limiting instrument maneuverability, preserves the nasoseptal vasculature for future NSF use if needed and appears to minimize the risks of postoperative arterial epistaxis and anosmia.

DNA methylation and gene deletion analysis of brain metastases in melanoma patients identifies mutually exclusive molecular alterations

BACKGROUND

The brain is a common target of metastases for melanoma patients. Little is known about the genetic and epigenetic alterations in melanoma brain metastases (MBMs). Unraveling these molecular alterations is a key step in understanding their aggressive nature and identifying novel therapeutic targets.

METHODS

Genome-wide DNA methylation analyses of MBMs (n = 15) and normal brain tissues (n = 91) and simultaneous multigene DNA methylation and gene deletion analyses of metastatic melanoma tissues (99 MBMs and 43 extracranial metastases) were performed. BRAF and NRAS mutations were evaluated in MBMs by targeted sequencing.

RESULTS

MBMs showed significant epigenetic heterogeneity. RARB, RASSF1, ESR1, APC, PTEN, and CDH13 genes were frequently hypermethylated. Deletions were frequently detected in the CDKN2A/B locus. Of MBMs, 46.1% and 28.8% had BRAF and NRAS missense mutations, respectively. Compared with lung and liver metastases, MBMs exhibited higher frequency of CDH13 hypermethylation and CDKN2A/B locus deletion. Mutual exclusivity between hypermethylated genes and CDKN2A/B locus deletion identified 2 clinically relevant molecular subtypes of MBMs. CDKN2A/B deletions were associated with multiple MBMs and frequently hypermethylated genes with shorter time to brain metastasis.

CONCLUSIONS

Melanoma cells that colonize the brain harbor numerous genetically and epigenetically altered genes. This study presents an integrated genomic and epigenomic analysis that reveals MBM-specific molecular alterations and mutually exclusive molecular subtypes.