Early expression of mature αß TCR in CD4-CD8- T cell progenitors enables MHC to drive development of T-ALL bearing NOTCH mutations.

During normal T cell development in mouse and human, a low-frequency population of immature CD4-CD8- double-negative (DN) thymocytes expresses early, mature αß T cell antigen receptor (TCR). We report that these early αß TCR+ DN (EADN) cells are DN3b-DN4 stage and require CD3δ but not major histocompatibility complex (MHC) for their generation/detection. When MHC - is present, however, EADN cells can respond to it, displaying a degree of coreceptor-independent MHC reactivity not typical of mature, conventional αß T cells. We found these data to be connected with observations that EADN cells were susceptible to T cell acute lymphoblastic leukemia (T-ALL) transformation in both humans and mice. Using the OT-1 TCR transgenic system to model EADN-stage αß TCR expression, we found that EADN leukemogenesis required MHC to induce development of T-ALL bearing NOTCH1 mutations. This leukemia-driving MHC requirement could be lost, however, upon passaging the tumors in vivo, even when matching MHC was continuously present in recipient animals and on the tumor cells themselves. These data demonstrate that MHC:TCR signaling can be required to initiate a cancer phenotype from an understudied developmental state that appears to be represented in the mouse and human disease spectrum.

Treatment response as predictor for brain metastasis in triple negative breast cancer: A score-based model.

BACKGROUND: Triple negative breast cancer (TNBC) has worse prognosis than other subtypes of breast cancer, and many patients develop brain metastasis (BM). We developed a simple predictive model to stratify the risk of BM in TNBC patients receiving neo-adjuvant chemotherapy (NAC), surgery, and radiation therapy (RT). METHODS: Patients with TNBC who received NAC, surgery, and RT were included. Cox proportional hazards method was used to evaluate factors associated with BM. Significant factors predictive for BM on multivariate analysis (MVA) were used to develop a risk score. Patients were divided into three risk groups: low, intermediate, and high. A receiver operating characteristic (ROC) curve was drawn to evaluate the value of the risk group in predicting BM. This predictive model was externally validated. RESULTS: A total of 160 patients were included. The median follow-up was 47.4 months. The median age at diagnosis was 49.9 years. The 2-year freedom from BM was 90.5%. Persistent lymph node positivity, HR 8.75 (1.76-43.52, P = 0.01), and lack of downstaging, HR 3.46 (1.03-11.62, P = 0.04), were significant predictors for BM. The 2-year rate of BM was 0%, 10.7%, and 30.3% (P < 0.001) in patients belonging to low-, intermediate-, and high-risk groups, respectively. Area under the ROC curve was 0.81 (P < 0.001). This model was externally validated (C-index = 0.79). CONCLUSIONS: Lack of downstaging and persistent lymph node positivity after NAC are associated with development of BM in TNBC. This model can be used by the clinicians to stratify patients into the three risk groups to identify those at increased risk of developing BM and potentially impact surveillance strategies.

Prognostic factors and survival patterns in pediatric low-grade gliomas over 4 decades.

BACKGROUND: This study reports changes in long-term survival after the introduction of modern imaging in pediatric patients with low-grade gliomas (LGGs). METHODS: Records from 351 consecutive pediatric patients diagnosed with LGG between 1970 and 2009 at Mayo Clinic Rochester were reviewed and divided into diagnosis before (group I: 1970 to 1989) and after (group II: 1990 to 2009) postoperative magnetic resonance imaging became regularly used in pediatric LGG. RESULTS: Median progression-free survival (PFS) and overall survival (OS) were not reached. Overall, 10-year PFS was 62% and OS was 90%. On multivariate analysis, improved PFS was associated with gross total resection (GTR; P<0.0001) and postoperative radiation therapy (RT; P<0.0001). In those undergoing less than GTR, PFS was improved with RT, nearing rates of patients receiving GTR (P=0.12). On multivariate analysis, higher OS was associated with GTR (P<0.0001) and pilocytic histology (P=0.03). Group II had fewer headaches, fewer sensory/motor symptoms, less postoperative RT, and more GTRs. OS and PFS were not different between the groups. CONCLUSIONS: This large series of pediatric LGG patients with long-term follow-up found no significant changes in OS or PFS over time. Overall, GTR was associated with improved OS and PFS. RT was associated with an improvement in PFS, with the greatest benefit seen in patients undergoing less than GTR.

Metastatic Neoplasm Volume Kinetics Following 2-Stage Stereotactic Radiosurgery.

BACKGROUND: Multisession staged stereotactic radiosurgery (SRS) represents an alternative approach for management of large brain metastases (LBMs), with potential advantages over fractionated SRS. This study investigated clinical efficacy and safety of 2-stage stereotactic radiosurgery (2-SSRS) in patients with LBMs. METHODS: Patients with LBMs treated with 2-SSRS between 2014 and 2020 were evaluated. Demographic, clinical, and radiologic data were obtained. Volumetric measurements at first SRS session, second SRS session, and follow-up imaging studies were obtained. Characteristics that might predict response to 2-SSRS were evaluated through Fisher exact or Mann-Whitney U test. RESULTS: The study included 24 patients with 26 LBMs. Median (range) marginal doses for first and second SRS sessions were 15 Gy (14-18 Gy) and 15 Gy (12-16 Gy), respectively. Median (range) tumor volumes at first SRS session, second SRS session, and 3-month follow-up were 8.1 cm3 (1.5-28.5 cm3), 3.3 cm3 (0.8-26.1 cm3), and 2.2 cm3 (0.2-10.1 cm3), respectively. Of 26 lesions, 24 (92%) demonstrated early local control following the first SRS session, with 17 lesions (71%) demonstrating a decrease of ≥30% in T1 postcontrast MRI volume before the second SRS session and 3 lesions (12%) remaining stable. Eventually, 4 lesions showed disease progression after 2-SSRS. The median time to local progression was not reached; the median time to intracranial progression was 9.1 months. CONCLUSIONS: Our study supports the effectiveness and safety of 2-SSRS as a treatment modality for patients with LBMs, especially in poor surgical candidates. The local failure rate and low occurrence of adverse effects are comparable to other staged radiosurgery studies.

The immune-related microRNA miR-146b is upregulated in glioblastoma recurrence.

BACKGROUND: Glioblastoma (GBM) has a high rate of local recurrence despite chemoradiotherapy (CRT). Genome-wide expression profiling was performed on patient tumors before and after chemoradiotherapy to identify genes and gene pathways associated with recurrence. RESULTS: Median time to recurrence was 8.9 months with median time to second surgery of 9.6 months. The microRNA (miRNA) analysis identified 9 oncologic and immune-related miRNAs to be differentially expressed, including the hypoxia-related miR-210 and the immune-modulatory miR-146b. More than 1200 differentially-expressed genes were identified with RNA-sequencing (RNA-seq). Gene set enrichment analysis (GSEA) identified p53 signaling, Notch, Wnt, VEGF, and MEK gene sets enriched in recurrent GBM. Consistent with the miRNA profiling data, the miR-146b target gene set from GSEA analysis was also associated with recurrence. METHODS: Fourteen patients with GBM recurrence after CRT who had available tumor tissue from the initial diagnosis as well as recurrence were selected. Total RNA was isolated from formalin-fixed paraffin-embedded (FFPE) tumor specimens. Genome-wide expression profiling using RT-PCR for miRNA analysis and RNA-seq for messenger RNA (mRNA) analysis were conducted to identify differentially-expressed genes. GSEA was performed on the differential expression data. CONCLUSIONS: Genome-wide expression profiling identifies multiple oncologic and immune-related gene sets associated with GBM recurrence. In particular, immune-related miR-146b is upregulated in recurrence and deserves further investigation.

Improved Metastasis- and Disease-Free Survival With Preoperative Sequential Short-Course Radiation Therapy and FOLFOX Chemotherapy for Rectal Cancer Compared With Neoadjuvant Long-Course Chemoradiotherapy: Results of a Matched Pair Analysis.

PURPOSE: To compare treatment and toxicity outcomes between a phase 2 institutional trial of near total neoadjuvant therapy (nTNT) for locally advanced rectal cancer and a similar historical control cohort treated at Washington University in St. Louis with the current US standard of care, defined as neoadjuvant chemoradiotherapy (NCRT), total mesorectal excision (TME), and adjuvant FOLFOX chemotherapy; to expand the comparison to an additional institution, patients treated with similar NCRT at Stanford University were included. METHODS AND MATERIALS: Sixty-nine patients with cT3-4N0-2M0 rectal adenocarcinoma enrolled on the Washington University in St. Louis phase 2 study of nTNT were included for analysis. Patients treated at the same institution with conventional NCRT and adjuvant FOLFOX were matched for exact cTNM stage. Forty-one patients treated with NCRT at Stanford University were included in a second analysis. Kaplan-Meier analysis with log-rank test was used to compare local control, distant metastasis-free survival, disease-free survival, and overall survival. RESULTS: Median follow-up was 49 and 54 months for nTNT and NCRT, respectively. Pathologic complete response and T-downstaging rates were 28% versus 16% (P=.21) and 75% versus 41% (P<.001) in the nTNT and NCRT cohorts, respectively. Three-year disease-free survival (85% vs 68%, P=.032) was significantly better in the nTNT group. Actuarial 3-year local control (92% vs 96%, P=.36) and overall survival (96% vs 88%, P=.67) were similar. The Stanford cohort had significantly lower clinical stage. After controlling for clinical stage, age, tumor location, institution, and number of chemotherapy cycles, nTNT treatment remained significantly associated with lower risk of recurrence (P=.006). CONCLUSIONS: Patients treated with nTNT had higher T-downstaging and superior distant metastasis-free survival and disease-free survival compared with conventional NCRT when matched for tumor location and exact cTNM stage. Near total neoadjuvant therapy remained a significant multivariate predictor for improved outcome when including patients treated with NCRT at another institution.

Prognostic microRNA signatures derived from The Cancer Genome Atlas for head and neck squamous cell carcinomas.

Identification of novel prognostic biomarkers typically requires a large dataset which provides sufficient statistical power for discovery research. To this end, we took advantage of the high-throughput data from The Cancer Genome Atlas (TCGA) to identify a set of prognostic biomarkers in head and neck squamous cell carcinomas (HNSCC) including oropharyngeal squamous cell carcinoma (OPSCC) and other subtypes. In this study, we analyzed miRNA-seq data obtained from TCGA patients to identify prognostic biomarkers for OPSCC. The identified miRNAs were further tested with an independent cohort. miRNA-seq data from TCGA was also analyzed to identify prognostic miRNAs in oral cavity squamous cell carcinoma (OSCC) and laryngeal squamous cell carcinoma (LSCC). Our study identified that miR-193b-3p and miR-455-5p were positively associated with survival, and miR-92a-3p and miR-497-5p were negatively associated with survival in OPSCC. A combined expression signature of these four miRNAs was prognostic of overall survival in OPSCC, and more importantly, this signature was validated in an independent OPSCC cohort. Furthermore, we identified four miRNAs each in OSCC and LSCC that were prognostic of survival, and combined signatures were specific for subtypes of HNSCC. A robust 4-miRNA prognostic signature in OPSCC, as well as prognostic signatures in other subtypes of HNSCC, was developed using sequencing data from TCGA as the primary source. This demonstrates the power of using TCGA as a potential resource to develop prognostic tools for improving individualized patient care.

High E6 Gene Expression Predicts for Distant Metastasis and Poor Survival in Patients With HPV-Positive Oropharyngeal Squamous Cell Carcinoma.

PURPOSE: Patients with human papillomavirus (HPV)-positive oropharyngeal squamous cell carcinoma (OPSCC) have a favorable prognosis. As a result, de-escalation clinical trials are under way. However, approximately 10% of patients will experience distant recurrence even with standard-of-care treatment. Here, we sought to identify novel biomarkers to better risk-stratify HPV-positive patients with OPSCC. METHODS AND MATERIALS: Gene expression profiling by RNA sequencing (RNA-seq) and quantitative polymerase chain reaction was performed on HPV-positive OPSCC primary tumor specimens from patients with and without distant metastasis (DM). RESULTS: RNA-seq analysis of 39 HPV-positive OPSCC specimens revealed that patients with DM had 2-fold higher E6 gene expression levels than did patients without DM (P=.029). This observation was confirmed in a validation cohort comprising 93 patients with HPV-positive OPSCC. The mean normalized E6 expression level in the 17 recurring primary specimens was 13 ± 2 compared with 8 ± 1 in the remaining 76 nonrecurring primaries (P=.001). Receiver operating characteristic analysis established an E6 expression level of 7.3 as a cutoff for worse recurrence-free survival (RFS). Patients from this cohort with high E6 gene expression (E6-high) (n=51, 55%) had more cancer-related deaths (23% vs 2%, P<.001) and DM (26% vs 5%, P<.001) than did patients with low E6 gene expression (E6-low) (n=42, 45%). Kaplan-Meier survival analysis revealed that E6-high had worse RFS (95% vs 69%, P=.004) and cancer-specific survival (97% vs 79%, P=.007). E6-high maintained statistical significance in multivariate regression models balancing surgery, chemotherapy, nodal stage, and smoking status. Gene set enrichment analysis demonstrated that tumors with high E6 expression were associated with P53, epidermal growth factor receptor, activating transcription factor-2, and transforming growth factor-ß signaling pathways. CONCLUSION: High E6 gene expression level identifies HPV-positive OPSCC patients with 5-fold greater risk of distant disease recurrence and worse cancer-specific survival. Validation in a multi-institutional prospective clinical trial is required to assess the utility of E6 gene expression as a clinically useful prognostic biomarker.

Quality of Life Outcomes From a Phase 2 Trial of Short-Course Radiation Therapy Followed by FOLFOX Chemotherapy as Preoperative Treatment for Rectal Cancer.

PURPOSE: A prospective phase 2 trial of short-course (SC) radiation therapy (RT) with 25 Gy over 5 fractions, followed by 4 cycles of 5-fluorouracil, oxaliplatin, and leucovorin (mFOLFOX6) before surgery was recently completed at our institution. We present here the patient-reported quality of life (QOL) outcomes from this trial. METHODS AND MATERIALS: Eighty patients with cT3/T4, any N, any M rectal adenocarcinoma planned for resection were enrolled between 2009 and 2012. The QOL data were obtained prospectively using the Functional Assessment of Cancer Therapy-Colon (FACT-C) questionnaire before RT, before surgery, and 1 year after surgery. The previously validated minimally importance difference (MID) method was used to measure clinically significant QOL changes in FACT-C scores for each patient across time points. We examined the role of ostomy on QOL. We also compared QOL with disease outcomes and physician-reported toxicity. RESULTS: The FACT-C questionnaire was completed by 97% of patients before RT, 85% immediately before surgery, and 62% 1 year after surgery. There was no statistically significant change in mean FACT-C scores from before treatment to after treatment. The majority of patients had either no change or an increase in QOL 1 year after treatment using the MID method. There were significant changes in QOL between patients with ostomy versus no ostomy 1 year after treatment for functional well-being (FWB) (14.81 vs 20.52, P=.018) and the colorectal cancer subscale (CCS) using the MID method (P=.004). Patients without ostomy reported stable changes in bowel control 1 year after surgery. There was no statistically significant correlation between QOL and disease recurrence, pathologic complete response, pathologic T stage downstaging, or acute/late toxicity. CONCLUSIONS: SC-RT and sequential mFOLFOX6 as preoperative therapy for rectal cancer results in stable patient-reported QOL outcomes 1 year after treatment. These findings in conjunction with previously reported oncologic outcomes support further evaluation of this regimen in a phase 3 setting.

Induction Chemotherapy Followed by Concurrent Full-dose Gemcitabine and Intensity-modulated Radiation Therapy for Borderline Resectable and Locally Advanced Pancreatic Adenocarcinoma.

OBJECTIVE: To evaluate the outcomes and toxicity of concurrent full-dose gemcitabine and intensity-modulated radiation therapy (IMRT) for patients with borderline resectable and locally advanced pancreatic adenocarcinoma after induction chemotherapy. MATERIALS AND METHODS: From 2009 to 2012, 32 patients were treated with concurrent gemcitabine and IMRT for borderline resectable or locally advanced pancreatic adenocarcinoma. All patients received induction FOLFIRINOX or gemcitabine-based chemotherapy before chemoradiation. The radiotherapy volume was limited to the primary tumor, and the median dose was 55 Gy in 25 fractions. Gemcitabine was administered weekly during radiotherapy on days 1, 8, 22, and 29 at a median weekly dose of 800 mg/m². RESULTS: Twenty-five patients had locally advanced disease and 7 had borderline resectable disease. The median follow-up time was 14.6 months. The median progression-free and overall survival were 13.9 and 23.1 months, with a trend toward improved overall survival for patients receiving induction FOLFIRINOX compared with gemcitabine-based therapy. A radiographic complete or partial response was achieved in 13 patients (41%), with 4 (13%) having complete radiographic responses. Surgical resection was performed in 10 patients (31%)--6 patients with locally advanced disease and 4 with borderline resectable disease. Grade 3/4 hematologic toxicity during and up to 6 weeks after chemoradiation occurred in 12 patients (38%); grade 3 nonhematologic toxicity occurred in 7 patients (22%), with no grade 4 or 5 toxicity. All patients completed their radiotherapy. CONCLUSIONS: Concurrent full-dose gemcitabine and limited-field IMRT after induction chemotherapy for the treatment of borderline resectable and locally advanced pancreatic cancer is promising with acceptable toxicity rates.

Lymphovascular space invasion and lack of downstaging after neoadjuvant chemotherapy are strong predictors of adverse outcome in young women with locally advanced breast cancer.

Younger age diagnosis of breast cancer is a predictor of adverse outcome. Here, we evaluate prognostic factors in young women with locally advanced breast cancer (LABC). We present a retrospective review of 104 patients younger than 40 years with LABC treated with surgery, radiotherapy (RT), and chemotherapy from 2003 to 2014. Patient-, tumor-, and treatment-related factors important for overall survival (OS), local/regional recurrence (LRR), distant metastasis (DM), and recurrence-free survival (RFS) were evaluated. Mean age at diagnosis was 34 years (23-39 years) with a median follow-up of 47 months (8-138 months). Breast-conserving surgery was performed in 27%. Axillary lymph node dissection was performed in 85%. Sixty percent of patients received neoadjuvant chemotherapy with 19% achieving pathologic complete response (pCR), and 61% downstaged. Lymph node positivity was present in 91% and lymphovascular space invasion (LVSI) in 35%. Thirty-two percent of patients had triple negative tumors (TN, ER-/PR-/HER2 nonamplified). Four-year OS and RFS was 84% and 71%, respectively. Factors associated with worse OS on multivariate analysis include TN status, LVSI, and number of positive lymph nodes. LVSI was also associated with DM and LRR, as well as worse RFS. Downstaging was associated with improved 4 year RFS in patients receiving neoadjuvant chemotherapy (74% vs. 38%, P = 0.002). With high risks of recurrence and inferior OS compared to older women, breast cancer in young women can be difficult to treat. Among additional factors, presence of LVSI and lack of downstaging portends a particularly worse prognosis.

Osteoradionecrosis of the temporal bone: a case series.

OBJECTIVE: To study osteoradionecrosis (ORN) of the temporal bone. STUDY DESIGN: Retrospective case review. SETTING: Academic medical center. PATIENTS: Patients were included who had previously undergone radiation to the head and neck and then developed exposed necrotic bone within the ear canal that persisted at least 3 months. INTERVENTIONS: Patients were treated with a variety of modalities, including conservative therapy with antibiotic ear drops and in-office debridements, hyperbaric oxygen therapy, and surgery. MAIN OUTCOME MEASURES: To describe the presentation and management of patients with temporal bone osteoradionecrosis. RESULTS: Thirty-three patients with temporal bone osteoradionecrosis were included. The most common site of primary tumor was the parotid gland (n = 11), followed by the nasopharynx (n = 7). The time to development of ORN varied between 1 and 22 years, with mean of 7.9 years. The mean radiation dose was 62.6 Gy to the primary tumor, 53.1 Gy to the affected temporal bone, and 65.2 Gy to the affected tympanic bone. The most common symptoms of ORN were otorrhea (n = 15), hearing loss (n = 13), and otalgia (n = 12). Fifteen patients had bacterial superinfection, most commonly Staphylococcus aureus (n = 9). Conservative therapy was successful at managing symptoms but not in eradicating exposed bone in most patients. Surgery was used for recalcitrant pain, infection, cholesteatoma, cranial neuropathies, and intracranial complications. CONCLUSION: Osteoradionecrosis is a rare complication of radiation to the temporal bone. Management should be aimed at relief of symptoms, eradication of superinfection, and treatment of other commonly present radiation effects like cholesteatoma and hearing loss.

Evaluating radiotherapy options in breast cancer: does intraoperative radiotherapy represent the most cost-efficacious option?

INTRODUCTION: This study analyzed the cost-efficacy of intraoperative radiation therapy (IORT) compared with whole-breast irradiation (WBI) and accelerated partial-breast irradiation (APBI) for early-stage breast cancer. MATERIALS AND METHODS: Data for this analysis came from 2 phase III trials: the TARGIT (Targeted Intraoperative Radiotherapy) trial and the ELIOT (Electron Intraoperative Radiotherapy) trial. Cost analyses included a cost-minimization analysis and an incremental cost-effectiveness ratio analysis including a quality-adjusted life-year (QALY) analysis. Cost analyses were performed comparing IORT with WBI delivered using 3-dimensional conformal radiotherapy (3D-CRT), APBI 3D-CRT, APBI delivered with intensity-modulated radiotherapy (IMRT), APBI single-lumen (SL), APBI multilumen (ML), and APBI interstitial (I). RESULTS: Per 1000 patients treated, the cost savings with IORT were $3.6-$4.3 million, $1.6-$2.4 million, $3.6-$4.4 million, $7.5-$8.2 million, and $2.8-$3.6 million compared with WBI 3D-CRT, APBI IMRT, APBI SL, APBI ML, and APBI I, respectively, with a cost decrement of $1.6-$2.4 million compared with APBI 3D-CRT based on data from the TARGIT trial. The costs per QALY for WBI 3D-CRT, APBI IMRT, APBI SL, APBI ML, and APBI I compared with IORT were $47,990-$60,002; $17,335-$29,347; $49,019-$61,031; $108,162-$120,173; and $36,129-$48,141, respectively, based on data from the ELIOT trial. These results are consistent with APBI and WBI being cost-effective compared with IORT. CONCLUSION: Based on cost-minimization analyses, IORT represents a potential cost savings in the management of early-stage breast cancer. However, absolute reimbursement is misleading, because when additional medical and nonmedical costs associated with IORT are factored in, WBI and APBI represent cost-effective modalities based on cost-per-QALY analyses. They remain the standard of care.

Brachytherapy-based partial breast irradiation is associated with low rates of complications and excellent cosmesis.

BACKGROUND: Recent retrospective, claims-based analyses have suggested a potential increased rate of toxicities associated with brachytherapy-based accelerated partial breast irradiation (APBI). The purpose of this analysis was to examine cosmesis and toxicity data from the prospective American Society of Breast Surgeons (ASBS) breast brachytherapy registry trial to compare to the findings from the claims analyses. METHODS: The ASBS breast brachytherapy registry is a prospective nonblinded multi-institutional registry trial. Patients with Stage 0-II breast cancer undergoing breast conserving therapy were eligible. A total of 1665 patients were enrolled and 1449 treated between 2002 and 2004 with a median followup of 63 months. All patients were treated with the MammoSite (Hologic, Inc.) single-lumen device to deliver adjuvant APBI (34Gy in 3.4Gy fractions). RESULTS: The rate of excellent/good cosmesis was 90.6% at 84 months. The rate of a complication (symptomatic seroma, infection, fat necrosis, telangiectasias) at 1 year/any time point was 24.2%/38.5%, whereas the rate of noninfectious complications at 1 year/any time point was 14.8%/28.9%. The rate of symptomatic seroma, fat necrosis, infection, and telangiectasia at any time was 13.4%, 2.5%, 9.6%, and 13.0%, respectively. CONCLUSIONS: The final toxicity analysis from ASBS breast brachytherapy registry trial confirms the previously noted excellent cosmesis and toxicity profiles and fails to confirm retrospective claims analyses that have suggested higher rates of toxicity for brachytherapy-based APBI.

HIV-1 Rev-binding protein accelerates cellular uptake of iron to drive Notch-induced T cell leukemogenesis in mice.

Somatic activating mutations in Notch1 contribute to the pathogenesis of T cell acute lymphoblastic lymphoma (T-ALL), but how activated Notch1 signaling exerts this oncogenic effect is not completely understood. Here we identify HIV-1 Rev-binding protein (Hrb), a component of the clathrin-mediated endocytosis machinery, as a critical mediator of Notch-induced T-ALL development in mice. Hrb was found to be a direct transcriptional target of Notch1, and Hrb loss reduced the incidence or delayed the onset of T-ALL in mouse models in which activated Notch1 signaling either contributes to or drives leukemogenesis. Consistent with this observation, Hrb supported survival and proliferation of hematopoietic and T cell precursor cells in vitro. We demonstrated that Hrb accelerated the uptake of transferrin, which was required for upregulation of the T cell protooncogene p21. Indeed, iron-deficient mice developed Notch1-induced T-ALL substantially more slowly than control mice, further supporting a critical role for iron uptake during leukemogenesis. Taken together, these results reveal that Hrb is a critical Notch target gene that mediates lymphoblast transformation and disease progression via its ability to satisfy the enhanced demands of transformed lymphoblasts for iron. Further, our data suggest that Hrb may be targeted to improve current treatment or design novel therapies for human T-ALL patients.

The transforming activity of Wnt effectors correlates with their ability to induce the accumulation of mammary progenitor cells.

Ectopic activation of the Wnt signaling pathway is highly oncogenic for many human tissues. Here, we show that ectopic Wnt signaling increases the effective stem cell activity in mouse mammary glands in vivo. Furthermore, Wnt effectors induce the accumulation of mouse mammary epithelial progenitors (assayed by Hoechst dye exclusion, a surrogate stem cell marker, side population cells) both in vivo and in vitro. The longevity of stem cells makes them good candidate tumor precursors, and we propose that Wnt-induced progenitor amplification is likely to be key to tumor initiation. In support of this notion, mammary glands from a tumor-resistant strain of mice (carrying a null mutation in syndecan-1) contain fewer side population cells. When this strain is crossed to mice that overexpress effectors of the beta-catenin/T cell factor Wnt pathway, the amplification of progenitors is reduced, together with all subsequent events of tumor development. We propose that the growth dynamic of the stem cell fraction is a major determinant of tumor susceptibility.