Predicting recurrence in pancreatic neuroendocrine tumours: role of ARX and alternative lengthening of telomeres (ALT).

BACKGROUND: While many pancreatic neuroendocrine tumours (PanNET) show indolent behaviour, predicting the biological behaviour of small nonfunctional PanNETs remains a challenge. Nonfunctional PanNETs with an epigenome and transcriptome that resemble islet alpha cells (ARX-positive) are more aggressive than neoplasms that resemble islet beta cells (PDX1-positive). In this study, we explore the ability of immunohistochemistry for ARX and PDX1 and telomere-specific fluorescence in situ hybridisation (FISH) for alternative lengthening of telomeres (ALT) to predict recurrence. METHODS: Two hundred fifty-six patients with PanNETs were identified, and immunohistochemistry for ARX and PDX1 was performed. Positive staining was defined as strong nuclear staining in >5% of tumour cells. FISH for ALT was performed in a subset of cases. RESULTS: ARX reactivity correlated with worse disease-free survival (DFS) (P = 0.011), while there was no correlation between PDX1 reactivity and DFS (P = 0.52). ALT-positive tumours (n = 63, 31.8%) showed a significantly lower DFS (P < 0.0001) than ALT-negative tumours (n = 135, 68.2%). ARX reactivity correlated with ALT positivity (P < 0.0001). Among nonfunctional tumours, recurrence was noted in 18.5% (30/162) of ARX-positive tumours and 7.5% (5/67) of ARX-negative tumours. Among WHO grade 1 and 2 PanNETs with ≤2 cm tumour size, 14% (6/43) of ARX-positive tumours recurred compared to 0 of 33 ARX-negative tumours and 33.3% (3/9) ALT-positive tumours showed recurrence versus 4.4% (2/45) ALT-negative tumours. CONCLUSION: Immunohistochemistry for ARX and ALT FISH status may aid in distinguishing biologically indolent cases from aggressive small low-grade PanNETs, and help to identify patients who may preferentially benefit from surgical intervention.

Therapeutic Vulnerability to ATR Inhibition in Concurrent NF1 and ATRX-Deficient/ALT-Positive High-Grade Solid Tumors.

Subsets of Neurofibromatosis Type 1 (NF1)-associated solid tumors have been shown to display high frequencies of ATRX mutations and the presence of alternative lengthening of telomeres (ALT). We studied the phenotype of combined NF1 and ATRX deficiency in malignant solid tumors. Cell lines derived from NF1-deficient sporadic glioblastomas (U251, SF188), an NF1-associated ATRX mutant glioblastoma cell line (JHH-NF1-GBM1), an NF1-derived sarcoma cell line (JHH-CRC65), and two NF1-deficient MPNST cell lines (ST88-14, NF90.8) were utilized. Cancer cells were treated with ATR inhibitors, with or without a MEK inhibitor or temozolomide. In contrast to the glioma cell line SF188, combined ATRX knockout (KO) and TERC KO led to ALT-like properties and sensitized U251 glioma cells to ATR inhibition in vitro and in vivo. In addition, ATR inhibitors sensitized U251 cells to temozolomide, but not MEK inhibition, irrespective of ATRX level manipulation; whereas, the JHH-NF1-GBM1 cell line demonstrated sensitivity to ATR inhibition, but not temozolomide. Similar effects were noted using the MPNST cell line NF90.8 after combined ATRX knockdown and TERC KO; however, not in ST88-14. Taken together, our study supports the feasibility of targeting the ATR pathway in subsets of NF1-deficient and associated tumors.

Novel forms of prostate cancer chemoresistance to successful androgen deprivation therapy demand new approaches: Rationale for targeting BET proteins.

In patients with prostate cancer, the duration of remission after treatment with androgen deprivation therapies (ADTs) varies dramatically. Clinical experience has demonstrated difficulties in predicting individual risk for progression due to chemoresistance. Drug combinations that inhibit androgen biosynthesis (e.g., abiraterone acetate) and androgen signaling (e.g., enzalutamide or apalutamide) have proven so effective that new forms of ADT resistance are emerging. In particular, prostate cancers with a neuroendocrine transcriptional signature, which demonstrate greater plasticity, and potentially, increased predisposition to metastasize, are becoming more prevalent. Notably, these subtypes had in fact been relatively rare before the widespread success of novel ADT regimens. Therefore, better understanding of these resistance mechanisms and potential alternative treatments are necessary to improve progression-free survival for patients treated with ADT. Targeting the bromodomain and extra-terminal (BET) protein family, specifically BRD4, with newer investigational agents may represent one such option. Several families of chromatin modifiers appear to be involved in ADT resistance and targeting these pathways could also offer novel approaches. However, the limited transcriptional and genomic information on ADT resistance mechanisms, and a serious lack of patient diversity in clinical trials, demand profiling of a much broader clinical and demographic range of patients, before robust conclusions can be drawn and a clear direction established.