Detection of Pathogenic Germline Variants Among Patients With Advanced Colorectal Cancer Undergoing Tumor Genomic Profiling for Precision Medicine.

BACKGROUND: Genomic profiling of colorectal cancer aims to identify actionable somatic mutations but can also discover incidental germline findings. OBJECTIVE: The purpose of this study was to report the detection of pathogenic germline variants that confer heritable cancer predisposition. DESIGN: This was a retrospective study. SETTINGS: The study was conducted at a tertiary-referral institution. PATIENTS: Between 2012 and 2015, 1000 patients with advanced cancer underwent targeted exome sequencing of a 202-gene panel. The subgroup of 151 patients with advanced colorectal cancer who underwent matched tumor-normal (blood) sequencing formed our study cohort. INTERVENTIONS: Germline variants in 46 genes associated with hereditary cancer predisposition were classified according to a defined algorithm based on in silico predictions of pathogenicity. Patients with presumed pathogenic variants were examined for type of mutation, as well as clinical, pedigree, and clinical genetic testing data. MAIN OUTCOME MEASURES: We measured detection of pathogenic germline variants. RESULTS: A total of 1910 distinct germline variants were observed in 151 patients. After filtering, 15 pathogenic germline variants (9.9%) were found in 15 patients, arising from 9 genes of varying penetrance for colorectal cancer (APC (n = 2; 13%), ATM (n = 1; 6%), BRCA1 (n = 2; 13%), CDH1 (n = 2; 13%), CHEK2 (n = 4; 27%), MSH2 (n = 1; 7%), MSH6 (n = 1; 7%), NF2 (n = 1; 7%), and TP53 (n = 1; 7%)). Patients with pathogenic variants were diagnosed at a younger age than those without (median, 45 vs 52 y; p = 0.03). Of the 15 patients, 7 patients (46.7%) with variants in low/moderate- penetrant genes for colorectal cancer would likely have not been tested based on clinical and pedigree criteria, where 2 harbored clinically actionable variants (CDH1 and NF2, 28.5% of 7). LIMITATIONS: This study was limited by its small sample size and advanced-stage patients. CONCLUSIONS: Tumor-normal sequencing can incidentally discover clinically unsuspected germline variants that confer cancer predisposition in 9.9% of patients with advanced colorectal cancer. Precision medicine should integrate clinical cancer genetics to inform and interpret the actionability of germline variants and to provide follow-up care to mutation carriers. See Video Abstract at http://links.lww.com/DCR/A906.

Accelerated enhanced Recovery following Minimally Invasive colorectal cancer surgery (RecoverMI): a study protocol for a novel randomised controlled trial.

INTRODUCTION: Definitive treatment of localised colorectal cancer involves surgical resection of the primary tumour. Short-stay colectomies (eg, 23-hours) would have important implications for optimising the efficiency of inpatient care with reduced resource utilisation while improving the overall recovery experience with earlier return to normalcy. It could permit surgical treatment of colorectal cancer in a wider variety of settings, including hospital-based ambulatory surgery environments. While a few studies have shown that discharge within the first 24 hours after minimally invasive colectomy is possible, the safety, feasibility and patient acceptability of a protocol for short-stay colectomy for colorectal cancer have not previously been evaluated in a prospective randomised study. Moreover, given the potential for some patients to experience a delay in recovery of bowel function after colectomy, close outpatient monitoring may be necessary to ensure safe implementation. METHODS AND ANALYSIS: In order to address this gap, we propose a prospective randomised trial of accelerated enhanced Recovery following Minimally Invasive colorectal cancer surgery (RecoverMI) that leverages the combination of minimally invasive surgery with enhanced recovery protocols and early coordinated outpatient remote televideo conferencing technology (TeleRecovery) to improve postoperative patien-provider communication, enhance postoperative treatment navigation and optimise postdischarge care. We hypothesise that RecoverMI can be safely incorporated into multidisciplinary practice to improve patient outcomes and reduce the overall 30-day duration of hospitalisation while preserving the quality of the patient experience. ETHICS AND DISSEMINATION: RecoverMI has received institutional review board approval and funding from the American Society of Colorectal Surgeons (ASCRS; LPG103). Results from RecoverMI will be published in a peer-reviewed publication and be used to inform a multisite trial. TRIAL REGISTRATION NUMBER: NCT02613728; Pre-results.

Nonoperative Management or 'Watch and Wait' for Rectal Cancer with Complete Clinical Response After Neoadjuvant Chemoradiotherapy: A Critical Appraisal.

BACKGROUND: There is increasing interest in nonoperative management (NOM) for rectal cancer with complete clinical response (cCR) after neoadjuvant chemoradiation (nCRT). OBJECTIVE: The aim of this systematic review was to summarize the available data on NOM, with the intention of formulating standardized protocols on which to base future investigations. METHODS: A systematic review following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines was conducted. A highly sensitive literature search identified all relevant studies published between January 2004 and December 2016. Data extraction and quality assessment was performed independently by two authors, and resolved by consensus with a third reviewer. RESULTS: In total, 15 studies, including 920 patients, met the inclusion criteria; 575 (62.5%) of these patients underwent NOM after cCR, with the remaining patients forming a surgical control group. The weighted mean follow-up was 39.4 (12.7) months in the NOM group and 39.8 (5.1) months in the surgery group. The pooled regrowth rate in the NOM group was 21.3% at a mean of 15.6 (7.0) months. Surgical salvage was possible and was undertaken in 93.2% of these patients. Overall survival in the NOM group was 91.7%, while disease-free survival was 82.7%. For the comparison proctectomy group, pooled rates of local recurrence, overall survival, and disease-free survival were 8.4, 92.4, and 87.5%, respectively. CONCLUSION: NOM may be a feasible option for surgically eligible rectal cancer patients with cCR after nCRT. Before such a strategy can be widely implemented, further prospective data are required with standardized definitions, diagnostic criteria, and management protocols, with an emphasis on shared patient-provider decision making and patient-centered outcomes.

Abrupt onset of mutations in a developmentally regulated gene during terminal differentiation of post-mitotic photoreceptor neurons in mice.

For sensitive detection of rare gene repair events in terminally differentiated photoreceptors, we generated a knockin mouse model by replacing one mouse rhodopsin allele with a form of the human rhodopsin gene that causes a severe, early-onset form of retinitis pigmentosa. The human gene contains a premature stop codon at position 344 (Q344X), cDNA encoding the enhanced green fluorescent protein (EGFP) at its 3' end, and a modified 5' untranslated region to reduce translation rate so that the mutant protein does not induce retinal degeneration. Mutations that eliminate the stop codon express a human rhodopsin-EGFP fusion protein (hRho-GFP), which can be readily detected by fluorescence microscopy. Spontaneous mutations were observed at a frequency of about one per retina; in every case, they gave rise to single fluorescent rod cells, indicating that each mutation occurred during or after the last mitotic division. Additionally, the number of fluorescent rods did not increase with age, suggesting that the rhodopsin gene in mature rod cells is less sensitive to mutation than it is in developing rods. Thus, there is a brief developmental window, coinciding with the transcriptional activation of the rhodopsin locus, in which somatic mutations of the rhodopsin gene abruptly begin to appear.

Rhodopsin gene expression determines rod outer segment size and rod cell resistance to a dominant-negative neurodegeneration mutant.

Two outstanding unknowns in the biology of photoreceptors are the molecular determinants of cell size, which is remarkably uniform among mammalian species, and the mechanisms of rod cell death associated with inherited neurodegenerative blinding diseases such as retinitis pigmentosa. We have addressed both questions by performing an in vivo titration with rhodopsin gene copies in genetically engineered mice that express only normal rhodopsin or an autosomal dominant allele, encoding rhodopsin with a disease-causing P23H substitution. The results reveal that the volume of the rod outer segment is proportional to rhodopsin gene expression; that P23H-rhodopsin, the most common rhodopsin gene disease allele, causes cell death via a dominant-negative mechanism; and that long term survival of rod cells carrying P23H-rhodopsin can be achieved by increasing the levels of wild type rhodopsin. These results point to promising directions in gene therapy for autosomal dominant neurodegenerative diseases caused by dominant-negative mutations.

Mislocalization and degradation of human P23H-rhodopsin-GFP in a knockin mouse model of retinitis pigmentosa.

PURPOSE: To engineer a knockin mouse model that can be used to monitor the effects of treatments on degradation and mislocalization of proline-to-histidine change at codon 23 (P23H) rhodopsin, a common cause of autosomal dominant retinitis pigmentosa (ADRP). The goal was to introduce a gene that expressed rhodopsin at low levels to avoid rapid retinal degeneration, and with a readily visible tag to make it easy to distinguish from wild type rhodopsin. METHODS: One copy of the endogenous mouse rhodopsin gene was replaced with a mutant human rhodopsin gene that encodes P23H-rhodopsin fused to enhanced green fluorescent protein (GFP) at its C terminus. The gene includes a LoxP site in the sequence corresponding to the 5'-untranslated region, which greatly reduces translation efficiency. Characterized are the resulting heterozygous and homozygous P23H-hRho-GFP mouse lines for mRNA and protein expression, P23H-rhodopsin localization in rod cells, effects on visual function, and retinal degeneration. RESULTS: The retinas of heterozygous P23H-hRho-GFP mice are morphologically and functionally very similar to those of wild type mice, and they display little cell death over time. P23H-hRho-GFP mice transcribe the knockin gene as efficiently as the endogenous mouse allele, but they contain much less of the protein product than do knockin mice expressing nonmutant hRho-GFP, indicating that substantial degradation of P23H-rRho-GFP occurs in mouse rod cells. The remaining P23H-hRho-GFP mislocalizes to the inner segment and outer nuclear layer, with only approximately 20% in rod outer segments. CONCLUSIONS: P23H-hRho-GFP mice provide a valuable tool for evaluating the efficacy of potential therapies for ADRP that influence the levels or localization of P23H-rhodopsin.

Genome-wide demethylation promotes triplet repeat instability independently of homologous recombination.

Trinucleotide repeat instability is intrinsic to a family of human neurodegenerative diseases. The mechanism leading to repeat length variation is unclear. We previously showed that treatment with the demethylating agent 5-aza-2'-deoxycytidine (5-aza-CdR) dramatically increases triplet repeat instability in mammalian cells. Based on previous reports that demethylation increases homologous recombination (HR), and our own observations that HR destabilizes triplet repeats, we hypothesized that demethylation alters repeat stability by stimulating HR. Here, we test that hypothesis at the adenosine phosphoribosyl transferase (Aprt) locus in CHO cells, where CpG demethylation and HR have both been shown to increase CAG repeat instability. We find that the rate of HR at the Aprt locus is not altered by demethylation. The spectrum of recombinants, however, was shifted from the usual 6:1 ratio of conversions to crossovers to more equal proportions in 5-aza-CdR-treated cells. The subtle influences of demethylation on HR at the Aprt locus are not sufficient to account for its dramatic effects on repeat instability. We conclude that 5-aza-CdR promotes triplet repeat instability independently of HR.