Let-7 Represses Carcinogenesis and a Stem Cell Phenotype in the Intestine via Regulation of Hmga2.

Let-7 miRNAs comprise one of the largest and most highly expressed family of miRNAs among vertebrates, and is critical for promoting differentiation, regulating metabolism, inhibiting cellular proliferation, and repressing carcinogenesis in a variety of tissues. The large size of the Let-7 family of miRNAs has complicated the development of mutant animal models. Here we describe the comprehensive repression of all Let-7 miRNAs in the intestinal epithelium via low-level tissue-specific expression of the Lin28b RNA-binding protein and a conditional knockout of the MirLet7c-2/Mirlet7b locus. This ablation of Let-7 triggers the development of intestinal adenocarcinomas concomitant with reduced survival. Analysis of both mouse and human intestinal cancer specimens reveals that stem cell markers were significantly associated with loss of Let-7 miRNA expression, and that a number of Let-7 targets were elevated, including Hmga1 and Hmga2. Functional studies in 3-D enteroids revealed that Hmga2 is necessary and sufficient to mediate many characteristics of Let-7 depletion, namely accelerating cell cycle progression and enhancing a stem cell phenotype. In addition, inactivation of a single Hmga2 allele in the mouse intestine epithelium significantly represses tumorigenesis driven by Lin28b. In aggregate, we conclude that Let-7 depletion drives a stem cell phenotype and the development of intestinal cancer, primarily via Hmga2.

Anal and Perineal Injuries.

With increased use of explosive devices in warfare, anal trauma is often seen coupled with more complex pelviperineal injury. While the associated mortality is high, casualties that survive are often left with disabling fecal incontinence from damage to the anosphincteric complex. After resolution of the acute insult, the initial evaluation mandates a thorough physical exam, including endoscopic evaluation with rigid proctoscopy and flexible sigmoidoscopy, as well as adjunctive testing, specifically anal manometry and endoanal ultrasound. First-line therapy favors bulking agents and antidiarrheals, in conjunction with biofeedback, due to a minimal risk profile. Surgical options range from direct sphincter repairs to complex anosphincteric reconstruction with widely variable results. Most recently, burgeoning therapies in the treatment of fecal incontinence, including sacral nerve stimulation and magnetic anal sphincters, offer excellent alternatives with promising long-term outcomes. In summation, the goal of all interventions is the re-establishment of bowel continence, but, in its absence, permanent fecal diversion for devastating fecal incontinence is a reasonable option with excellent patient satisfaction scores.

Colorectal Specialization Increases Lymph Node Yield: Evidence from a National Database.

BACKGROUND: Current guidelines recommend the evaluation of at least 12 lymph nodes (LNs) in the pathologic specimen following surgery for colorectal cancer (CRC). We sought to examine the role of colorectal specialization on nodal identification. METHODS: We conducted a retrospective cohort study using SEER-Medicare data to examine the association between colorectal specialization and LN identification following surgery for colon and rectal adenocarcinoma between 2001 and 2009. Our dataset included patients >65 years who underwent surgical resection for CRC. We excluded patients with rectal cancer who had received neoadjuvant therapy. The primary outcome measure was the number of LNs identified in the pathologic specimen following surgery for CRC. Multivariate analysis was used to identify the association between surgical specialization and LN identification in the pathologic specimen. RESULTS: In multivariate analysis, odds of an adequate lymphadenectomy following surgery with a colorectal specialist were 1.32 and 1.41 times greater for colon and rectal cancer, respectively, than following surgery by a general surgeon (p < 0.001). These odds increased to 1.36 and 1.58, respectively, when analysis was limited to board-certified colorectal surgeons. Hospital factors associated with ≥12 LNs identified included high-volume CRC surgery (colon OR 1.84, p < 0.001; rectal OR 1.78, p < 0.001) and NCI-designated Cancer Centers (colon OR 1.75, p < 0.001; rectal OR 1.64; p = 0.007). CONCLUSIONS: Colorectal specialization and, in particular, board-certification in colorectal surgery, is significantly associated with increased LN identification following surgery for colon and rectal adenocarcinoma since the adoption of the 12-LN guideline in 2001.

A Nomogram to Predict Lymph Node Positivity Following Neoadjuvant Chemoradiation in Locally Advanced Rectal Cancer.

BACKGROUND: Patients with locally advanced rectal cancer typically receive neoadjuvant chemoradiation followed by total mesorectal excision. Other treatment approaches, including transanal techniques and close surveillance, are becoming increasingly common following positive responses to chemoradiation. Lack of pathologic lymph node staging is one major disadvantage of these novel strategies. OBJECTIVE: The purposes of this study were to determine clinicopathologic factors associated with positive lymph nodes following neoadjuvant chemoradiation for rectal cancer and to create a nomogram using these factors to predict rates of lymph node positivity. DESIGN: This is a retrospective cohort analysis. SETTINGS: This study used the National Cancer Database. PATIENTS: Patients aged 18 to 90 with clinical stage T3/T4, N0, M0 or Tany, N1-2, M0 adenocarcinoma of the rectum who underwent neoadjuvant chemoradiation before total mesorectal excision from 2010 to 2012 were identified. MAIN OUTCOME MEASURES: The primary outcome measure was lymph node positivity after neoadjuvant chemoradiation for locally advanced rectal cancer. Bivariate and multivariate analyses were used to determine the associations of clinicopathologic variables with lymph node positivity. RESULTS: Eight thousand nine hundred eighty-four patients were included. Young age, lower Charlson score, mucinous histology, poorly differentiated and undifferentiated tumors, the presence of lymphovascular invasion, elevated CEA level, and clinical lymph node positivity were significantly predictive of pathologic lymph node positivity following neoadjuvant chemoradiation. The predictive accuracy of the nomogram is 70.9%, with a c index of 0.71. There was minimal deviation between the predicted and observed outcomes. LIMITATIONS: This study is retrospective, and it cannot be determined when in the course of treatment the data were collected. CONCLUSIONS: We created a nomogram to predict lymph node positivity following neoadjuvant chemoradiation for locally advanced rectal cancer that can serve as a valuable complement to imaging to aid clinicians and patients in determining the best treatment strategy.

Lymph node identification following neoadjuvant therapy in rectal cancer: A stage-stratified analysis using the surveillance, epidemiology, and end results (SEER)-medicare database.

BACKGROUND AND OBJECTIVES: Neoadjuvant chemoradiation (nCRT) for rectal adenocarcinoma reduces lymph node (LN) identification following surgical resection. We sought to evaluate the relationship between LN identification following nCRT and disease-specific survival (DSS), stratified by pathologic stage. METHODS: The SEER-Medicare database (2000-2009) was queried for 1,216 pathologic stage I-III rectal cancer patients who underwent nCRT followed by curative-intent resection. Cox regressions evaluated the association between pathologic stage and DSS for LN cut-points from ≥2 up to ≥12 LNs. RESULTS: Extent of LN identification did not influence DSS in ypStage I or ypStage III disease; in particular, the 12 LN cut-point was not associated with DSS for ypStage I (HR 1.29, P = 0.51) or ypStage III (HR 1.08, P = 0.42) patients. In ypStage II patients, actuarial survival improved continually with increasing lymph node identification up to ≥12 LNs. The 5 LN cut-point was associated with the greatest reduction of risk of cancer death (HR 0.56, P = 0.006), with decreasing magnitudes of survival benefit associated with nodal counts beyond 5 LN. The 12 LN cut-point was not associated with DSS in ypStage II patients (HR 0.67, P = 0.07). CONCLUSION: The association between DSS and LN identification is a dynamic outcome that varies by pathologic stage, with unique prognostic significance for ypStage II patients.

Survival outcomes of anal adenocarcinoma versus rectal adenocarcinoma: A retrospective cohort study.

BACKGROUND: Anal adenocarcinoma (AA) is a rare malignancy with decreased survival compared to rectal adenocarcinoma (RA). However, AA continues to be treated with similar algorithms compared to rectal cancer with minimal data regarding the efficacy of these treatment algorithms. METHODS: A retrospective chart review of patients with non-metastatic AA at a single tertiary-care institution from 1995 to 2020. This cohort was matched 2:1 to a group of RA patients for comparison. The primary outcome of interest was overall survival rates. RESULTS: Sixteen patients with stages I-III AA were matched to a cohort of RA. There were no significant differences between the cohorts with regard to patient demographics, comorbidities, disease stage or histologic features. There were also no significant differences in treatment modalities between the two cohorts with a majority undergoing multimodal therapy with chemoradiation and surgery. All patients with AA demonstrated significantly worse survival than all patients with rectal adenocarcinoma (five-year survival 47.7% vs. 82.3%, respectively. p < 0.05). When looking at a sub-group of patients who underwent combination chemoradiation and surgery from each cohort, anal adenocarcinoma continued to exhibit lower overall survival (five-year survival 41.6% and 86.4%, respectively. p < 0.05). In a multi-variable model that adjusted for location, American Joint Committee on Cancer (AJCC) stage and treatment pathway, tumor location in the anal canal was an independent predictor of overall survival (Hazard ratio [HR] 2.7, p < 0.05). CONCLUSION: AA has worse survival as compared to RA despite similar treatment. This study highlights the need to evaluate the current classification and treatment pathways to improve outcomes.

Differential Regulation of LET-7 by LIN28B Isoform-Specific Functions.

The RNA-binding protein LIN28B plays an important role in development, stem cell biology, and tumorigenesis. LIN28B has two isoforms: the LIN28B-long and -short isoforms. Although studies have revealed the functions of the LIN28B-long isoform in tumorigenesis, the role of the LIN28B-short isoform remains unclear and represents a major gap in the field. The LIN28B-long and -short isoforms are expressed in a subset of human colorectal cancers and adjacent normal colonic mucosa, respectively. To elucidate the functional and mechanistic aspects of these isoforms, colorectal cancer cells (Caco-2 and LoVo) were generated to either express no LIN28B or the -short or -long isoform. Interestingly, the long isoform suppressed LET-7 expression and activated canonical RAS/ERK signaling, whereas the short isoform did not. The LIN28B-long isoform-expressing cells demonstrated increased drug resistance to 5-fluorouracil and cisplatin through the upregulation of ERCC1, a DNA repair gene, in a LET-7-dependent manner. The LIN28B-short isoform preserved its ability to bind pre-let-7, without inhibiting the maturation of LET-7, and competed with the LIN28B-long isoform for binding to pre-let-7 Coexpression of the short isoform in the LIN28B-long isoform-expressing cells rescued the phenotypes induced by the LIN28B-long isoform.Implications: This study demonstrates the differential antagonistic functions of the LIN28B-short isoform against the LIN28B-long isoform through an inability to degrade LET-7, which leads to the novel premise that the short isoform may serve to counterbalance the long isoform during normal colonic epithelial homeostasis, but its downregulation during colonic carcinogenesis may reveal the protumorigenic effects of the long isoform. Mol Cancer Res; 16(3); 403-16. ©2018 AACR.

The frequency of double-positive thymocytes expressing an alphabeta TCR clonotype regulates peripheral CD4 T cell compartment homeostasis.

The present study aimed to determine whether the frequency of double positive (DP) thymocytes expressing alphabeta T-cell receptor (TCR) clonotypes at the time of selection regulates peripheral CD4 T-cell compartment size. Scid recipients were inoculated with various ratios of TCR Calpha(0/0) and wild-type bone marrow (BM) stem cells. Increasing the frequency of TCR Calpha(0/0) thymocytes at steady-state introduced a graded decrease in the maturation probability of the total DP thymocyte pool. At 12-14 weeks following BM inoculation, the frequency of TCR Calpha(0/0) DP thymocytes was inversely correlated with that of CD4 single positive (SP) thymocytes. Notwithstanding, a decreased frequency of wild-type DP thymocytes led to a marked increase in their transit efficiency from the DP to SP compartments. The frequency-dependent increase in thymocyte transit efficiency was associated with a CD4 SP cell surface phenotype indicative of increased antigenic experience. Importantly, the frequency of DP thymocytes capable of expressing TCR clonotypes dictated the steady-state size of the peripheral CD4 T cell compartment and its potential for homeostatic proliferation. Collectively, these results indicate that the efficiency of DP to CD4 SP transit is a frequency dependent process, which determines (1) the steady-state size of the peripheral T cell compartment and (2) the threshold for homeostatic expansion of peripheral CD4 T cells.

Alloreactive CD4 T cell activation in vivo: an autonomous function of the indirect pathway of alloantigen presentation.

Activation of alloreactive CD4 T cells occurs via the direct and indirect pathways of alloantigen presentation. A novel TCR/alloantigen transgenic system was designed that permitted in vivo visualization of CD4 T cell priming through these pathways. When both pathways of alloantigen presentation were intact, CD4 T cell activation in response to cardiac allografts was rapid and systemic by day 4 after transplantation, in contrast to that seen in response to skin allografts, which was delayed until 10-12 days after transplantation. Despite this systemic CD4 T cell activation in response to cardiac allografts, there was a paucity of activated graft-infiltrating CD4 T cells at 4 days posttransplantation. This finding suggests that the initial priming of alloimmune CD4 T cell responses occurs within draining lymphoid organs. Furthermore, alloantigens derived from cardiac allografts failed to promote thymic negative selection of developing thymocytes expressing the alloreactive TCR clonotype. In the absence of a functional direct pathway, the kinetics of activation, anatomic localization, and effector function of alloreactive CD4 T cells remained unchanged. Overall, the present study defines the anatomic and temporal characteristics of CD4 T cell alloimmune responses and demonstrates that CD4 T cell priming via the indirect pathway proceeds optimally in the absence of the direct pathway of alloantigen presentation.