Universal mean-field upper bound for the generalization gap of deep neural networks

Modern deep neural networks (DNNs) represent a formidable challenge for theorists: according to the commonly accepted probabilistic framework that describes their performance, these architectures should overfit due to the huge number of parameters to train, but in practice they do not. Here we employ results from replica mean field theory to compute the generalization gap of machine learning models with quenched features, in the teacher-student scenario and for regression problems with quadratic loss function. Notably, this framework includes the case of DNNs where the last layer is optimized given a specific realization of the remaining weights. We show how these results-combined with ideas from statistical learning theory-provide a stringent asymptotic upper bound on the generalization gap of fully trained DNN as a function of the size of the dataset P. In particular, in the limit of large P and N_{out} (where N_{out} is the size of the last layer) and N_{out}≪P, the generalization gap approaches zero faster than 2N_{out}/P, for any choice of both architecture and teacher function. Notably, this result greatly improves existing bounds from statistical learning theory. We test our predictions on a broad range of architectures, from toy fully connected neural networks with few hidden layers to state-of-the-art deep convolutional neural networks.

Radiation-induced acute dysphagia : Prospective observational study on 42 head and neck cancer patients

PURPOSE

Acute toxicity in head and neck (H&N) cancer patients treated with definitive radiotherapy (RT) has a crucial role in compliance to treatments. The aim of this study was to correlate doses to swallowing-associated structures and acute dysphagia.

METHODS

We prospectively analyzed 42 H&N cancer patients treated with RT. Dysphagia (grade ≥ 3) and indication for percutaneous endoscopic gastrostomy (PEG) insertion were classified as acute toxicity. Ten swallowing-related structures were considered for the dosimetric analysis. The correlation between clinical information and the dose absorbed by the contoured structures was analyzed. Multivariate logistic regression method using resampling methods (bootstrapping) was applied to select model order and parameters for normal tissue complication probability (NTCP) modelling.

RESULTS

A strong multiple correlation between dosimetric parameters was found. A two-variable model was suggested as the optimal order by bootstrap method. The optimal model (Rs = 0.452, p < 0.001) includes V₄₅ of the cervical esophagus (odds ratio [OR] = 1.016) and D_mean of the cricopharyngeal muscle (OR = 1.057). The model area under the curve was 0.82 (95% confidence interval 0.69-0.95).

CONCLUSION

Our results suggested that the absorbed dose to the cricopharyngeal muscle and cervical esophagus might play a relevant role in the development of acute RT-related dysphagia.

Effect of preoperative chemoradiotherapy on outcome of patients with locally advanced esophagogastric junction adenocarcinoma-a pilot study

BACKGROUND

To date, few studies of preoperative chemotherapy or chemoradiotherapy (crt) in gastroesophageal junction (gej) cancer have been statistically powered; indeed, gej tumours have thus far been grouped with esophageal or gastric cancer in phase iii trials, thereby generating conflicting results.

METHODS

We studied 41 patients affected by locally advanced Siewert type i and ii gej adenocarcinoma who were treated with a neoadjuvant crt regimen [folfox4 (leucovorin-5-fluorouracil-oxaliplatin) for 4 cycles, and concurrent computed tomography-based three-dimensional conformal radiotherapy delivered using 5 daily fractions of 1.8 Gy per week for a total dose of 45 Gy], followed by surgery. Completeness of tumour resection (performed approximately 6 weeks after completion of crt), clinical and pathologic response rates, and safety and outcome of the treatment were the main endpoints of the study.

RESULTS

All 41 patients completed preoperative treatment. Combined therapy was well tolerated, with no treatment-related deaths. Dose reduction was necessary in 8 patients (19.5%). After crt, 78% of the patients showed a partial clinical response, 17% were stable, and 5% experienced disease progression. Pathology examination of surgical specimens demonstrated a 10% complete response rate. The median and mean survival times were 26 and 36 months respectively (95% confidence interval: 14 to 37 months and 30 to 41 months respectively). On multivariate analysis, TNM staging and clinical response were demonstrated to be the only independent variables related to long-term survival.

CONCLUSIONS

In our experience, preoperative chemoradiotherapy with folfox4 is feasible in locally advanced gej adenocarcinoma, but shows mild efficacy, as suggested by the low rate of pathologic complete response.

Phorbol 12-myristate 13-acetate (pma) induces neuroendocrine-like differentiation and reverses Doxorubicin-resistance of human colon-carcinoma cells in-vitro

Human colon carcinoma LoVo/DX cells, which have been selected from parental LoVo for resistance to doxorubicin, express a typical multidrug resistant (MDR-1) phenotype. We have investigated whether phorbol 12-myristate 13-acetate (PMA) which often induces phenotypical changes in human tumor cells could, at the same time, modulate differentiation and sensitivity of LoVo/DX cells to doxorubicin. After 48 h exposure to 100 nM PMA, morphological changes became evident on LoVo/DX cells which showed elongated cytoplasm and dendritic-like structures: moreover immunocytochemical findings were suggestive of neuroendocrine-like differentiation. Under the same experimental conditions, LoVo/DX became sensitive to doxorubicin and showed enhanced intracellular drug-accumulation and reduced membrane expression of the 170 kD glycoprotein GP-170, which is the cellular product of the mdr1 gene. We conclude that pharmacological induction of tumor cell differentiation by PMA is paralleled by abrogation of drug resistance in a colon carcinoma MDR-1 cell line.

Complete response to preoperative chemoradiation and survival in esophageal cancer: a pooled analysis of three single-institution phase II trials

This pooled analysis was performed using individual patient data from three phase II trials that included on the whole 113 esophageal cancer treated preoperatively with chemoradiotherapy (CRT), in order to analyze the efficacy and survival outcomes according to the achievement of the pathologic complete response (pCR). Thirty-nine patients were treated with 5-fluorouracil/cisplatin and RT (40 Gy), 33 patients received paclitaxel/cisplatin weekly during weeks 1-6 with and RT (46 Gy), 41 patients were treated with induction bio-chemotherapy with cetuximab and FOLFOX-4 followed by concomitant cetuximab and RT of 50.4 Gy. One hundred and two out of 113 resected patients were included in the survival analysis. The median overall survival (OS) time for the whole population was 21.5 months. The 12, 24, and 36 months OS rates were 85.4, 45.2, and 33%, respectively. The difference in survival probability between patients with pCR and patients with partial response or stable disease after treatment was significant (P= 0.0002, hazard ratios = 0.21, 95% CI 0.18-0.60). On multivariate analysis, the pathologic response and histology were the only covariates independently associated with OS (P= 0.0157 and P= 0.0212, respectively). In our series, complete responder patients had a significant longer survival probability after treatment when compared to patients with partial response or stable disease.

Neo-adjuvant treatment of rectal cancer with capecitabine and oxaliplatin in combination with radiotherapy: a phase II study

BACKGROUND

Preoperative chemoradiation is now standard treatment for stages II-III rectal cancer. Capecitabine (CAP) and oxaliplatin (OX) are synergistic with radiotherapy (RT) and active in colorectal neoplasms.

PATIENTS AND METHODS

Two cycles of CAP 825 mg/m(2) b.i.d. (days 1-14) and OX 50 mg/m(2) (days 1 and 8) every 3 weeks were given concomitantly with pelvic conformal RT (45 Gy). Patients with a > or =T3 and/or node-positive rectal tumour were eligible. The pathologic tumour response was defined according to the tumour regression grade (TRG) scale.

RESULTS

Forty-six patients were enrolled. Gastrointestinal adverse events were mostly G1-G2; only two patients experienced G3 vomiting and diarrhoea and six patients had G1 peripheral neuropathy. Haematological toxicity was rare. G2 proctitis and anal pain occurred in two patients. Pathological complete response (TRG1) was observed in nine patients (20.9%; 95% CI 8.7%-33.1%); TRG2 in 19 patients (44.2%); TRG3 in 12 patients (27.9%); and TRG4 in three patients (7%). Overall, nine patients recurred: five with distant metastases, one with local recurrence, and three with both local recurrence and distant metastases.

CONCLUSIONS

CAP-OX-RT as preoperative treatment for rectal cancer induces a remarkable rate of complete or near-complete pathologically documented response and is well tolerated.

Early clinical and neuroradiological worsening after radiotherapy and concomitant temozolomide in patients with glioblastoma: tumour progression or radionecrosis?

OBJECTIVES

This study investigates the diagnosis and management of patients with resected brain glioblastomas who presented early clinical and neuroradiological worsening after the completion of the Stupp protocol. Its aim is to discuss the occurrence of early radionecrosis.

METHODS

Fifty patients with brain glioblastoma treated by surgical resection and Stupp protocol were reviewed; 15 among them (30%) had early clinical and neuroradiological worsening at the 6-month follow-up. The MR spectroscopy and surgical findings of these patients are reviewed.

RESULTS

MR spectroscopy was in favour of tumour recurrence in 14 among 15 patients and showed radionecrosis in one. Among 10 patients who were reoperated on, 7 had histologically verified tumour recurrence or regrowth, whereas in 3 histopathology showed necrosis without evidence of tumour. The 7 patients with tumour progression had prevalence of focal neuroradiological signs (6/7) and a survival of 7.5-12 months (median survival 10 months). The 4 patients with early radionecrosis (including one patient who was not reoperated on) had clinical worsening with mental deterioration, confusion and ataxia, and MR spectroscopy positive for tumour recurrence in 3. Three were alive 24-30 months after the end of the radiotherapy, whereas one died at 40 months.

CONCLUSION

Early radionecrosis after the Stupp protocol is not a rare event due to the radiosensitization effect of temozolomide. This phenomenon may predict a durable response to radiotherapy. MR spectroscopy may simulate tumour recurrence. A correct diagnosis is necessary to avoid useless reoperations and incorrect withdrawal of temozolomide.

Involvement of H4(D10S170) protein in ATM-dependent response to DNA damage

H4(D10S170) gene has been identified upon its frequent rearrangement with RET in papillary thyroid tumours (RET/PTC1). The kinase ataxia telangectasia mutated (ATM) phosphorylates a limited number of downstream protein targets in response to DNA damage. We investigated the potential role of H4(D10S170) in DNA damage signaling pathways. We found that in cells treated with etoposide or ionizing radiation (IR), H4(D10S170) underwent ATM-mediated phosphorylation at Thr 434, stabilizing nuclear H4. In ataxia telangectasia cells (A-T), endogenous H4(D10S170) was localized to cytoplasm and was excluded from the nucleus. Moreover, H4(D10S170) was not phosphorylated in ATM-deficient lymphoblasts after ionizing irradiation. Inhibition of ATM kinase interfered with H4(D10S170) apoptotic activity, and expression of H4 with threonine 434 mutated in Alanine, H4(T434A), protected the cells from genotoxic stress-induced apoptosis. Most importantly, after exposure to IR we found that silencing of H4(D10S170) in mammalian cells increased cell survival, as shown by clonogenic assay, allows for DNA synthesis as evaluated by bromodeoxyuridine incorporation and permits cells to progress into mitosis as demonstrated by phosphorylation on Histone H3. Our results suggest that H4(D10S170) is involved in cellular response to DNA damage ATM-mediated, and that the impairment of H4(D10S170) gene function might have a role in thyroid carcinogenesis.

Comparison of control of Listeria by nitric oxide redox chemistry from murine macrophages and NO donors: insights into listeriocidal activity of oxidative and nitrosative stress

The physiological function of nitric oxide (NO) in the defense against pathogens is multifaceted. The exact chemistry by which NO combats intracellular pathogens such as Listeria monocytogenes is yet unresolved. We examined the effects of NO exposure, either delivered by NO donors or generated in situ within ANA-1 murine macrophages, on L. monocytogenes growth. Production of NO by the two NONOate compounds PAPA/NO (NH2(C3H6)(N[N(O)NO]C3H7) and DEA/NO (Na(C2H5)2N[N(O)NO]) resulted in L. monocytogenes cytostasis with minimal cytotoxicity. Reactive oxygen species generated from xanthine oxidase/hypoxanthine were neither bactericidal nor cytostatic and did not alter the action of NO. L. monocytogenes growth was also suppressed upon internalization into ANA-1 murine macrophages primed with interferon-gamma (INF-gamma) + tumor necrosis factor-alpha (TNF-alpha or INF-gamma + lipid polysaccharide (LPS). Growth suppression correlated with nitrite formation and nitrosation of 2,3-diaminonaphthalene elicited by stimulated murine macrophages. This nitrosative chemistry was not dependent upon nor mediated by interaction with reactive oxygen species (ROS), but resulted solely from NO and intermediates related to nitrosative stress. The role of nitrosation in controlling L. monocytogenes was further examined by monitoring the effects of exposure to NO on an important virulence factor, Listeriolysin O, which was inhibited under nitrosative conditions. These results suggest that nitrosative stress mediated by macrophages is an important component of the immunological arsenal in controlling L. monocytogenes infections.