Immune checkpoint inhibitors in non-small cell lung cancer - When should we dare to stop treatment?

Over the last years, the emergence of immune checkpoint inhibitors (ICI) has revolutionized the treatment of non-small cell lung cancer (NSCLC). Patients in a palliative setting with previously very poor prognosis may now show remarkable responses over years. Yet, ICI therapy is very cost-intensive and involves frequent contacts with healthcare resources. Some of the early trial protocols restricted ICI treatment duration to two years. Now follow-up data of these studies is available and reveal the possibility of a persistent response after two or more years without further treatment for patients having successfully completed two years of therapy. May we now dare to think (and speak) of cure in the palliative setting? Does it mean we can stop ICI therapy after an initial two-year treatment? In this review, we try to improve confidence in clinical decision-making for this patient group. To this end, trials with a restricted treatment duration of two years and other data considering potential ICI discontinuation in responding patients were evaluated. Up to 25% of patients successfully complete an initial two-year course of ICI. Within this group about 40-46% of patients are alive at five years without further treatment with five-year survival rates of up to 83%. Data on ICI rechallenge are scarce, yet it does not seem to provide the same level of efficacy as at first exposure. At present there are no established biomarkers to help with decision-making. Possible future (bio-)markers, such as PD-L1, mutations, circulating tumor DNA (ctDNA) or Positron emission tomography (PET) need to be evaluated further in a prospective setting. In conclusion, we propose that the concept of discontinuing ICI therapy in patients with tumor response has to be seriously taken into consideration as it may be of benefit to our patients and health care systems.

Protocol of the TREASURE study: Thoracic RadiothErapy with Atezolizumab in Small cell lUng canceR Extensive disease - a randomized, open-label, multicenter phase II trial.

BACKGROUND: Recently, the combination of the programmed death-ligand 1 (PD-L1) inhibitor atezolizumab with first-line chemotherapy has demonstrated to improve outcome for patients with advanced small cell lung cancer (SCLC), leading to approval of this regimen. At the same time, accumulating (pre-)clinical data suggest synergisms of radiotherapy and immunotherapy via the radiation-mediated induction of anti-tumor immunogenicity. Combining the recent findings, the TREASURE trial aims at further enhancing response to upfront chemo-immunotherapy by the addition of thoracic radiotherapy (TRT). METHODS/DESIGN: The TREASURE trial is a randomized, multicenter, phase II clinical trial ( ClinicalTrials.gov identifier, NCT04462276). One hundred four patients suffering from extensive disease (ED) SCLC, with any response to the standard of care induction chemo-immunotherapy will be randomized to receive atezolizumab maintenance therapy with or without TRT. The primary endpoint of this study is overall survival (OS). Secondary endpoints include further measures of efficacy, safety, and the collection of biomarker samples. A safety interim analysis will take place after n = 23 patients receiving TRT have been observed for three months after the end of TRT. DISCUSSION: This trial will investigate whether treatment efficacy can be improved by adding TRT to atezolizumab maintenance therapy in ED SCLC patients with any response after chemo-immunotherapy. Safety and feasibility of such a regimen will be evaluated, and biomaterials for a translational research project will be collected. Together, the results of this trial will deepen our comprehension of how checkpoint inhibition and radiotherapy interact and contribute to the evolving landscape of SCLC therapy. TRIAL REGISTRATION: Clinicaltrials.gov identifier: NCT04462276 (Date of initial registration: 8th July 2020), https://clinicaltrials.gov/ct2/show/NCT04462276 Eudra-CT Number: 2019-003916-29 (Date of initial registration: 30th March 2020), https://www.clinicaltrialsregister.eu/ctr-search/trial/2019-003916-29/DE.

PITX1 Is a Regulator of TERT Expression in Prostate Cancer with Prognostic Power.

The current risk stratification in prostate cancer (PCa) is frequently insufficient to adequately predict disease development and outcome. One hallmark of cancer is telomere maintenance. For telomere maintenance, PCa cells exclusively employ telomerase, making it essential for this cancer entity. However, TERT, the catalytic protein component of the reverse transcriptase telomerase, itself does not suit as a prognostic marker for prostate cancer as it is rather low expressed. We investigated if, instead of TERT, transcription factors regulating TERT may suit as prognostic markers. To identify transcription factors regulating TERT, we developed and applied a new gene regulatory modeling strategy to a comprehensive transcriptome dataset of 445 primary PCa. Six transcription factors were predicted as TERT regulators, and most prominently, the developmental morphogenic factor PITX1. PITX1 expression positively correlated with telomere staining intensity in PCa tumor samples. Functional assays and chromatin immune-precipitation showed that PITX1 activates TERT expression in PCa cells. Clinically, we observed that PITX1 is an excellent prognostic marker, as concluded from an analysis of more than 15,000 PCa samples. PITX1 expression in tumor samples associated with (i) increased Ki67 expression indicating increased tumor growth, (ii) a worse prognosis, and (iii) correlated with telomere length.

Brigatinib versus other second-generation ALK inhibitors as initial treatment of anaplastic lymphoma kinase positive non-small cell lung cancer with deep phenotyping: study protocol of the ABP trial.

BACKGROUND: Availability of potent anaplastic lymphoma kinase (ALK) tyrosine kinase inhibitors (TKI) has pushed the median survival of ALK+ non-smallcell lung cancer (NSCLC) patients to over five years. In particular, second-generation ALK TKI have demonstrated superiority compared to the first-generation compound crizotinib and are meanwhile standard first-line treatment. However, clinical courses of individual patients vary widely, with secondary development of drug resistance and intracranial progression remaining important problems. While these limitations highlight the need for better disease monitoring and additional therapeutic tools, molecular tumor features are increasingly recognized as crucial determinants of clinical outcome. This trial aims to optimize management of ALK+ NSCLC by analyzing the efficacy of second-generation ALK inhibitors in conjunction with deep longitudinal phenotyping across two treatment lines. METHODS/DESIGN: In this exploratory prospective phase II clinical trial, newly diagnosed ALK+ NSCLC patients will be randomized into two treatment arms, stratified by presence of brain metastases and ECOG performance status: brigatinib (experimental arm) vs. any other approved second-generation ALK TKI. Tumor tissue and blood samples will be collected for biomarker analysis at the beginning and throughout the study period to investigate baseline molecular tumor properties and analyze the development of acquired drug resistance. In addition, participating investigators and patients will have the possibility of fast-track molecular tumor and ctDNA profiling at the time of disease progression using state-of-the-art next-generation sequencing (NGS), in order to support decisions regarding next-line therapy. DISCUSSION: Besides supporting therapeutic decisions for enrolled patients, the ABP trial primarily aims to deepen the understanding of the underlying biology and facilitate development of a framework for individualized management of ALK+ NSCLC according to molecular features. Patients with low molecular risk and the perspective of a "chronic disease" will be distinguished from "high-risk" cases, molecular properties of which will be utilized to elaborate improved methods of non-invasive monitoring and novel preclinical models in order to advance therapeutic strategies. TRIAL REGISTRATION: Clinicaltrials.gov , NCT04318938. Registered March 182,020, https://www.clinicaltrials.gov/ct2/show/NCT04318938 Eudra-CT, 2019-001828-36. Registered September 302,019, https://www.clinicaltrialsregister.eu/ctr-search/search?query=2019-001828-36.

De Novo Versus Secondary Metastatic EGFR-Mutated Non-Small-Cell Lung Cancer.

BACKGROUND: Metastatic epidermal growth factor receptor-mutated (EGFR+) non-small-cell lung cancer (NSCLC) can present de novo or following previous nonmetastatic disease (secondary). Potential differences between these two patient subsets are unclear at present. METHODS: We retrospectively analyzed characteristics of tyrosine kinase inhibitor (TKI)-treated patients with de novo vs. secondary metastatic EGFR+ NSCLC until December 2019 (n = 401). RESULTS: De novo metastatic disease was 4× more frequent than secondary (n = 83/401), but no significant differences were noted regarding age (median 66 vs. 70 years), sex (65% vs. 65% females), smoking history (67% vs. 62% never/light-smokers), and histology (both >95% adenocarcinoma). Patients with secondary metastatic disease showed a better ECOG performance status (PS 0-1 67%-32% vs. 46%-52%, p = 0.003), fewer metastatic sites (mean 1.3 vs. 2.0, p < 0.001), and less frequent brain involvement (16% vs. 28%, p = 0.022) at the time of stage IV diagnosis. Progression-free survival (PFS) under TKI (median 17 for secondary vs. 12 months for de novo, p = 0.26) and overall survival (OS, 29 vs. 25 months, respectively, p = 0.47) were comparable. EGFR alterations (55% vs. 60% exon 19 deletions), TP53 mutation rate at baseline (47% vs. 43%, n = 262), and T790M positivity at the time of TKI failure (51% vs. 56%, n = 193) were also similar. OS according to differing characteristics, e.g., presence or absence of brain metastases (19-20 or 30-31 months, respectively, p = 0.001), and ECOG PS 0 or 1 or 2 (32-34 or 20-23 or 5-7 months, respectively, p < 0.001), were almost identical for de novo and secondary metastatic disease. CONCLUSIONS: Despite the survival advantage reported in the pre-TKI era for relapsed NSCLC, molecular features and outcome of TKI-treated metastatic EGFR+ tumors are currently independent of preceding nonmetastatic disease. This simplifies design of outcome studies and can assist prognostic considerations in everyday management of patients with secondary metastatic EGFR+ tumors.

A Phase II Trial of Nivolumab With Chemotherapy Followed by Maintenance Nivolumab in Patients With Pleural Mesothelioma After Surgery: The NICITA Study Protocol.

BACKGROUND: In selected patients with early-stage malignant pleural mesothelioma (MPM), a multimodal therapy that includes surgical cytoreduction, chemotherapy, and/or radiotherapy is recommended. Several clinical trials have demonstrated the beneficial effects of immune checkpoint inhibitors in pretreated MPM patients with advanced disease. Recent clinical data have suggested that the combination of chemotherapy and checkpoint inhibition might improve efficacy. TRIAL DESIGN: The NICITA (nivolumab with chemotherapy in pleural mesothelioma after surgery) trial is a prospective, 1:1 randomized, open-label, multicenter phase II clinical trial (ClinicalTrials.gov identifier, NCT04177953). Ninety-two patients with MPM epithelioid subtype, who had undergone extended pleurectomy and decortication with or without hyperthermic intrathoracic chemoperfusion, will be included to receive adjuvant treatment. All patients will receive ≤ 4 cycles of platinum-based chemotherapy with pemetrexed (arms A and B). Patients in arm B will additionally receive nivolumab, together with the adjuvant chemotherapy, and subsequently for ≤ 12 cycles as maintenance therapy. The primary endpoint of this study is the time-to-next-treatment. The secondary endpoints include progression-free survival, overall survival, proportion of patients with treatment beyond progression, duration of treatment beyond progression in this population, and quality of life. CONCLUSION: This prospective trial will contribute data to assess the efficacy of standard chemotherapy combined with nivolumab in the context of multimodal management of early-stage MPM. The study is currently enrolling patients.

Thoracic radiotherapy plus Durvalumab in elderly and/or frail NSCLC stage III patients unfit for chemotherapy - employing optimized (hypofractionated) radiotherapy to foster durvalumab efficacy: study protocol of the TRADE-hypo trial.

BACKGROUND: Non-small cell lung cancer is the most common cause of cancer death worldwide, highlighting the need for novel therapeutic concepts. In particular, there is still a lack of treatment strategies for the group of elderly and frail patients, who are frequently not capable of receiving standard therapy regimens. Despite comprising the majority of lung cancer patients, this group is underrepresented in clinical trials. This applies also to elderly and frail patients suffering from unresectable stage III NSCLC, who are unfit for chemotherapy, and, therefore, cannot receive the standard therapy comprising of radiochemotherapy and the recently approved subsequent durvalumab consolidation therapy. These patients often receive radiotherapy only, which raises the concern of undertreatment. The TRADE-hypo trial aims at optimizing treatment of this patient group by combining radiotherapy with concomitant durvalumab administration, thereby employing the immune-promoting effects of radiotherapy, and determining safety, feasibility, and efficacy of this treatment. METHODS/ DESIGN: In this prospective phase II clinical trial, durvalumab therapy will be combined with either conventionally fractionated (CON-group) or hypofractionated (HYPO-group) thoracic radiotherapy. A safety stop-and-go lead-in phase will assess safety of hypofractionated radiotherapy with respect to severe pneumonitis in small patient cohorts before opening full enrollment. Tumor tissue, blood and stool samples will be collected before and during the study period to investigate the immunological mechanisms responsible for checkpoint inhibitor efficacy and immune-promoting effects of radiotherapy. DISCUSSION: Preclinical data suggests that irradiation-induced immunogenicity can be further increased if applied in a hypofractionated setting, potentially boosting the expected synergistic effect with immune checkpoint inhibition in restoring the immune anti-tumor response. If proven safe and efficient, a hypofractionated radiation schedule can provide a considerably more practicable option for the patient. Taking into consideration the intend to develop a combination treatment strategy that can be made available to patients soon after proving to be efficient and the potentially elevated toxicity of a hypofractionated radiotherapy approach, this trial was designed as a two-trials-in-one design. An accompanying translational research program is planned striving to gain insights into the tumor-host biology and to identify suitable biomarkers to predict therapy response. TRIAL REGISTRATION: Clinicaltrials.gov , NCT04351256 . Registered 17 April 2020, Eudra-CT, 2019-002192-33 . Registered 24 October 2019.

Paclitaxel for treatment of advanced small cell lung cancer (SCLC): a retrospective study of 185 patients.

BACKGROUND: Etoposide-/platinum-based chemotherapy is the standard first-line treatment for extensive-disease small cell lung cancer (SCLC), but responses are short-lived and subsequent options limited. Here, we present our experience with paclitaxel in advanced treatment lines. METHODS: We retrospectively studied the clinical course of all paclitaxel-treated SCLC patients between 2005 and 2015 in our institution. Prognostic and predictive factors were analyzed by Kaplan-Meier and Cox regression analyses. RESULTS: A total of 185 patients [119 men, median age 65 years, median ECOG performance status (PS) 1] were identified. One hundred and sixty-eight patients had extensive disease (ED) at the time of paclitaxel therapy. Paclitaxel was mainly given as third- or fourth-line therapy (93%). The response rate (RR) was 17% and disease control rate (DCR) 28%. Patients reached a median progression-free survival (PFS) of 1.6 (95% CI: 1.4-1.8) months and median overall survival (OS) of 3.3 (95% CI: 2.8-3.9) months. Main toxicities were fatigue (25%) and polyneuropathy (17%). Dose reduction of ≥25% was associated with shorter PFS [1.9 (95% CI: 1.5-2.3) vs. 1.4 (95% CI: 1.3-1.5) months; P=0.004]. Further independent predictive factors for PFS were gender, age, and hepatic/brain metastases (P<0.05). Tumor response to paclitaxel, PS, number and location of metastases, dose reduction, and smoking history were significant factors for OS in univariable analyses (P<0.05), while PS, dose reduction, status of cerebral/hepatic metastases, tumor response, and smoking history were retained as independent prognostic factors in multivariable testing. Notably, ECOG PS 2 patients had toxicity rates similar to ECOG PS 0-1 patients (63% vs. 62%), as well as a comparable DCR (29% vs. 28%), which was associated with prolonged survival (4.5 vs. 3.2 months for refractory cases, P=0.034). CONCLUSIONS: Paclitaxel has clinically relevant activity in heavily pretreated SCLC. While patients with good PS and no cerebral/hepatic metastases derive the greatest benefit, ECOG PS 2 per se should not be used as a criterion to exclude patients.

TelNet - a database for human and yeast genes involved in telomere maintenance.

BACKGROUND: The ends of linear chromosomes, the telomeres, comprise repetitive DNA sequences in complex with proteins that protects them from being processed by the DNA repair machinery. Cancer cells need to counteract the shortening of telomere repeats during replication for their unlimited proliferation by reactivating the reverse transcriptase telomerase or by using the alternative lengthening of telomeres (ALT) pathway. The different telomere maintenance (TM) mechanisms appear to involve hundreds of proteins but their telomere repeat length related activities are only partly understood. Currently, a database that integrates information on TM relevant genes is missing. DESCRIPTION: To provide a resource for studies that dissect TM features, we here introduce the TelNet database at http://www.cancertelsys.org/telnet/ . It offers a comprehensive compilation of more than 2000 human and 1100 yeast genes linked to telomere maintenance. These genes were annotated in terms of TM mechanism, associated specific functions and orthologous genes, a TM significance score and information from peer-reviewed literature. This TM information can be retrieved via different search and view modes and evaluated for a set of genes as demonstrated for an exemplary application. CONCLUSION: TelNet supports the annotation of genes identified from bioinformatics analysis pipelines to reveal possible connections with TM networks. We anticipate that TelNet will be a helpful resource for researchers that study telomeres.

Integrative genomic and transcriptomic analysis of leiomyosarcoma.

Leiomyosarcoma (LMS) is an aggressive mesenchymal malignancy with few therapeutic options. The mechanisms underlying LMS development, including clinically actionable genetic vulnerabilities, are largely unknown. Here we show, using whole-exome and transcriptome sequencing, that LMS tumors are characterized by substantial mutational heterogeneity, near-universal inactivation of TP53 and RB1, widespread DNA copy number alterations including chromothripsis, and frequent whole-genome duplication. Furthermore, we detect alternative telomere lengthening in 78% of cases and identify recurrent alterations in telomere maintenance genes such as ATRX, RBL2, and SP100, providing insight into the genetic basis of this mechanism. Finally, most tumors display hallmarks of "BRCAness", including alterations in homologous recombination DNA repair genes, multiple structural rearrangements, and enrichment of specific mutational signatures, and cultured LMS cells are sensitive towards olaparib and cisplatin. This comprehensive study of LMS genomics has uncovered key biological features that may inform future experimental research and enable the design of novel therapies.

Quantification of telomere features in tumor tissue sections by an automated 3D imaging-based workflow.

The microscopic analysis of telomere features provides a wealth of information on the mechanism by which tumor cells maintain their unlimited proliferative potential. Accordingly, the analysis of telomeres in tissue sections of patient tumor samples can be exploited to obtain diagnostic information and to define tumor subgroups. In many instances, however, analysis of the image data is conducted by manual inspection of 2D images at relatively low resolution for only a small part of the sample. As the telomere feature signal distribution is frequently heterogeneous, this approach is prone to a biased selection of the information present in the image and lacks subcellular details. Here we address these issues by using an automated high-resolution imaging and analysis workflow that quantifies individual telomere features on tissue sections for a large number of cells. The approach is particularly suited to assess telomere heterogeneity and low abundant cellular subpopulations with distinct telomere characteristics in a reproducible manner. It comprises the integration of multi-color fluorescence in situ hybridization, immunofluorescence and DNA staining with targeted automated 3D fluorescence microscopy and image analysis. We apply our method to telomeres in glioblastoma and prostate cancer samples, and describe how the imaging data can be used to derive statistically reliable information on telomere length distribution or colocalization with PML nuclear bodies. We anticipate that relating this approach to clinical outcome data will prove to be valuable for pretherapeutic patient stratification.

Cancer Cells with Alternative Lengthening of Telomeres Do Not Display a General Hypersensitivity to ATR Inhibition.

Telomere maintenance is a hallmark of cancer as it provides cancer cells with cellular immortality. A significant fraction of tumors uses the alternative lengthening of telomeres (ALT) pathway to elongate their telomeres and to gain an unlimited proliferation potential. Since the ALT pathway is unique to cancer cells, it represents a potentially valuable, currently unexploited target for anti-cancer therapies. Recently, it was proposed that ALT renders cells hypersensitive to ataxia telangiectasia- and RAD3-related (ATR) protein inhibitors (Flynn et al., Science 347, 273). Here, we measured the response of various ALT- or telomerase-positive cell lines to the ATR inhibitor VE-821. In addition, we compared the effect of the inhibitor on cell viability in isogenic cell lines, in which ALT was active or suppressed. In these experiments, a general ATR inhibitor sensitivity of cells with ALT could not be confirmed. We rather propose that the observed variations in sensitivity reflect differences between cell lines that are unrelated to ALT.

SUMOylation of Rad52-Rad59 synergistically change the outcome of mitotic recombination.

Homologous recombination (HR) is essential for maintenance of genome stability through double-strand break (DSB) repair, but at the same time HR can lead to loss of heterozygosity and uncontrolled recombination can be genotoxic. The post-translational modification by SUMO (small ubiquitin-like modifier) has been shown to modulate recombination, but the exact mechanism of this regulation remains unclear. Here we show that SUMOylation stabilizes the interaction between the recombination mediator Rad52 and its paralogue Rad59 in Saccharomyces cerevisiae. Although Rad59 SUMOylation is not required for survival after genotoxic stress, it affects the outcome of recombination to promote conservative DNA repair. In some genetic assays, Rad52 and Rad59 SUMOylation act synergistically. Collectively, our data indicate that the described SUMO modifications affect the balance between conservative and non-conservative mechanisms of HR.

DNA break-induced sumoylation is enabled by collaboration between a SUMO ligase and the ssDNA-binding complex RPA.

Upon genome damage, large-scale protein sumoylation occurs from yeast to humans to promote DNA repair. Currently, the underlying mechanism is largely unknown. Here we show that, upon DNA break induction, the budding yeast SUMO ligase Siz2 collaborates with the ssDNA-binding complex RPA (replication protein A) to induce the sumoylation of recombination factors and confer damage resistance. Both RPA and nuclease-generated ssDNA promote Siz2-mediated sumoylation. Mechanistically, the conserved Siz2 interaction with RPA enables Siz2 localization to damage sites. These findings provide a molecular basis for recruiting SUMO ligases to the vicinity of their substrates to induce sumoylation upon DNA damage.

PML induces compaction, TRF2 depletion and DNA damage signaling at telomeres and promotes their alternative lengthening.

The alternative lengthening of telomeres (ALT) mechanism allows cancer cells to escape senescence and apoptosis in the absence of active telomerase. A characteristic feature of this pathway is the assembly of ALT-associated promyelocytic leukemia (PML) nuclear bodies (APBs) at telomeres. Here, we dissected the role of APBs in a human ALT cell line by performing an RNA interference screen using an automated 3D fluorescence microscopy platform and advanced 3D image analysis. We identified 29 proteins that affected APB formation, which included proteins involved in telomere and chromatin organization, protein sumoylation and DNA repair. By integrating and extending these findings, we found that APB formation induced clustering of telomere repeats, telomere compaction and concomitant depletion of the shelterin protein TRF2 (also known as TERF2). These APB-dependent changes correlated with the induction of a DNA damage response at telomeres in APBs as evident by a strong enrichment of the phosphorylated form of the ataxia telangiectasia mutated (ATM) kinase. Accordingly, we propose that APBs promote telomere maintenance by inducing a DNA damage response in ALT-positive tumor cells through changing the telomeric chromatin state to trigger ATM phosphorylation.

Regulation of Ku-DNA association by Yku70 C-terminal tail and SUMO modification.

The Ku70-Ku80 ring complex encloses DNA ends to facilitate telomere maintenance and DNA break repair. Many studies focus on the ring-forming regions of subunits Ku70 and Ku80. Less is known about the Ku70 C-terminal tail, which lies outside the ring. Our results suggest that this region is responsible for dynamic sumoylation of Yku70 upon DNA association in budding yeast. Mutating a cluster of five lysines in this region largely eliminates Yku70 sumoylation. Chromatin immunoprecipitation analyses show that yku70 mutants with these lysines replaced by arginines exhibit reduced Ku-DNA association at both telomeres and internal DNA breaks. Consistent with this physical evidence, Yku70 sumoylation deficiency is associated with impaired ability to block DNA end resection and suppression of multiple defects caused by inefficient resection. Correlating with these, yku70 mutants with reduced sumoylation levels exhibit shorter telomeres, increased G overhang levels, and altered levels of non-homologous end joining. We also show that diminution of sumoylation does not affect Yku70 protein levels or its interactions with protein and RNA partners. These results suggest a model whereby Yku70 sumoylation upon DNA association strengthens Ku-DNA interaction to promote multiple functions of Ku.

PML body meets telomere: the beginning of an ALTernate ending?

The unlimited proliferation potential of cancer cells requires the maintenance of their telomeres. This is frequently accomplished by reactivation of telomerase. However, in a significant fraction of tumors an alternative lengthening of telomeres (ALT) mechanism is active. The molecular mechanism of the ALT pathway remains elusive. In particular, the role of characteristic complexes of promyelocytic leukemia nuclear bodies (PML-NBs) with telomeres, the ALT-associated PML-NBs (APBs), is currently under investigation. Here, we review recent findings on the assembly, structure and functions of APBs. It is discussed how genomic aberrations in ALT-positive cancer cells could result in the formation of APBs and in ALT activity. We conclude that they are important functional intermediates in what is considered the canonical ALT pathway and discuss deregulations of cellular pathways that contribute to the emergence of the ALT phenotype.