Kathryn E. Huber

Filamentous phage integration requires the host recombinases XerC and XerD

Many bacteriophages and animal viruses integrate their genomes into the chromosomal DNA of their hosts as a method of promoting vertical transmission. Phages that integrate in a site-specific fashion encode an integrase enzyme that catalyses recombination between the phage and host genomes. CTXφ is a filamentous bacteriophage that contains the genes encoding cholera toxin, the principal virulence factor of the diarrhoea-causing Gram-negative bacterium Vibrio cholerae. CTXφ integrates into the V. cholerae genome in a site-specific manner; however, the ∼6.9-kilobase (kb) CTXφ genome does not encode any protein with significant homology to known recombinases. Here we report that XerC and XerD, two chromosome-encoded recombinases that ordinarily function to resolve chromosome dimers at the dif recombination site, are essential for CTXφ integration into the V. cholerae genome. The CTXφ integration site was found to overlap with the dif site of the larger of the two V. cholerae chromosomes. Examination of sequences of the integration sites of other filamentous phages indicates that the XerCD recombinases also mediate the integration of these phage genomes at dif-like sites in various bacterial species.

Breast Cancer Molecular Subtypes in Patients With Locally Advanced Disease: Impact on Prognosis, Patterns of Recurrence, and Response to Therapy

Gene expression profiling has led to the discovery of 4 distinct molecular subtypes of breast cancer: luminal A, luminal B, basal like, and HER2 enriched. Investigation of these subtypes in women with breast cancer has given insight into the heterogeneous biology and outcomes in patients with locally advanced disease. These subtypes have been found to be predictors for survival, response to systemic therapy, and locoregional recurrence. This review discusses the biology of locally advanced breast cancer and the available data on how molecular subtype may provide information regarding response to treatment and prognosis of women with locally advanced breast cancer.

BEDVH--A method for evaluating biologically effective dose volume histograms: Application to eye plaque brachytherapy implants

PURPOSE A method is introduced to examine the influence of implant duration T, radionuclide, and radiobiological parameters on the biologically effective dose (BED) throughout the entire volume of regions of interest for episcleral brachytherapy using available radionuclides. This method is employed to evaluate a particular eye plaque brachytherapy implant in a radiobiological context. METHODS A reference eye geometry and 16 mm COMS eye plaque loaded with (103)Pd, (125)I, or (131)Cs sources were examined with dose distributions accounting for plaque heterogeneities. For a standardized 7 day implant, doses to 90% of the tumor volume ( (TUMOR)D(90)) and 10% of the organ at risk volumes ( (OAR)D(10)) were calculated. The BED equation from Dale and Jones and published α/β and μ parameters were incorporated with dose volume histograms (DVHs) for various T values such as T = 7 days (i.e.,  (TUMOR) (7)BED(10) and  (OAR) (7)BED(10)). By calculating BED throughout the volumes, biologically effective dose volume histograms (BEDVHs) were developed for tumor and OARs. Influence of T, radionuclide choice, and radiobiological parameters on  (TUMOR)BEDVH and  (OAR)BEDVH were examined. The nominal dose was scaled for shorter implants to achieve biological equivalence. RESULTS  (TUMOR)D(90) values were 102, 112, and 110 Gy for (103)Pd, (125)I, and (131)Cs, respectively. Corresponding  (TUMOR) (7)BED(10) values were 124, 140, and 138 Gy, respectively. As T decreased from 7 to 0.01 days, the isobiologically effective prescription dose decreased by a factor of three. As expected,  (TUMOR) (7)BEDVH did not significantly change as a function of radionuclide half-life but varied by 10% due to radionuclide dose distribution. Variations in reported radiobiological parameters caused  (TUMOR) (7)BED(10) to deviate by up to 46%. Over the range of (OAR)α/β values,  (OAR) (7)BED(10) varied by up to 41%, 3.1%, and 1.4% for the lens, optic nerve, and lacrimal gland, respectively. CONCLUSIONS BEDVH permits evaluation of the relative biological effectiveness for brachytherapy implants. For eye plaques,  (TUMOR)BEDVH and  (OAR)BEDVH were sensitive to implant duration, which may be manipulated to affect outcomes.

Locally Advanced Pancreatic Cancer. Looking Beyond Traditional Chemotherapy and Radiation

About a third of all pancreatic cancer is found to be locally advanced at the time of diagnosis, where the tumor is inoperable but remains localized to the pancreas and regional lymphatics. Sadly, this remains a universally deadly disease with progression to distant disease being the predominant mode of failure and average survival under one year. Optimal treatment of these patients continues to be an area of controversy, with chemotherapy alone being the treatment preference in Europe, and chemotherapy followed by chemoradiation in selected patients, preferred in the USA. The aim of this paper is to summarize the key abstracts presented at the 2013 ASCO Annual Meeting that address evolving approaches to the management of locally advanced pancreatic cancer. The late breaking abstract (#LBA4003) provided additional European data showing non-superiority of chemoradiation compared to chemotherapy in locally advanced pancreatic cancer patients without distant progression following 4 months of chemotherapy. Another late breaking abstract, (#LBA4004), unfortunately showed a promising new complement to gemcitabine and capecitabine using immunotherapy in the form of a T-helper vaccine did not translate to improved survival in the phase III setting.

The Implications of Breast Cancer Molecular Phenotype for Radiation Oncology

The identification of distinct molecular subtypes of breast cancer has advanced the understanding and treatment of breast cancer by providing insight into prognosis, patterns of recurrence, and effectiveness of therapy. The prognostic significance of molecular phenotype with regard to distant recurrences and overall survival are well established in the literature and has been readily incorporated into systemic therapy management decisions. However, despite the accumulating data suggesting similar prognostic significance for locoregional recurrence, integration of molecular phenotype into local management decision making has lagged. Although there are some conflicting reports, collectively the literature supports a low risk of local recurrence (LR) in the hormone receptor (HR) positive luminal subtypes compared to HR negative subtypes [triple negative (TN) and HER2-enriched]. The development of targeted therapies, such as trastuzumab for the treatment of HER2-enriched subtype, has been shown to mitigate the increased risk of LR. Unfortunately, no such remedy exists to address the increased risk of LR for patients with TN tumors, making it a clinical challenge for radiation oncologists. In this review we discuss the correlation between molecular subtype and LR following either breast conservation therapy or mastectomy. We also explore the possible mechanisms for increased LR in TN breast cancer and radiotherapeutic implications for this population, such as the safety of breast conservation, consideration of dose escalation, and the appropriateness of accelerated partial breast irradiation.

Novel Treatment Approaches for Locally Advanced Pancreatic Cancer

Despite decades of research, pancreatic cancer remains essentially incurable for patients with unresectable tumors. In the United States, most patients with locally advanced pancreatic cancer are treated with chemotherapy alone or combined with conventionally fractionated radiotherapy. Regardless of the treatment strategy, average survival for these patients is less than 1 year, indicating that the current approaches are indisputably inadequate. For locally advanced pancreatic cancer patients, effective local-regional control is not only crucial for any hope at long-term survival, but also for symptom management. The aim of this paper is to highlight abstracts from the 2014 ASCO Gastrointestinal Cancers Symposium that demonstrate the use of novel local-regional therapies in locally advanced pancreatic cancer. Abstracts #317, #328, and #361 describe their results with an advanced method of delivering radiation called stereotactic body radiation therapy (SBRT). In these studies, patients treated with combined chemotherapy and SBRT had exceptional local control rates and acceptable toxicity. An innovative alternative to radiation for local-regional treatment is presented in Abstract #270. This study shows encouraging results from a phase I investigation of a regionally delivered siRNA that targets the K-ras(G12D) mutation. Investigation of novel approaches such as those presented here holds the greatest promise for improving treatment of this deadly disease.

Phase 1 Trials in Pancreatic Cancer

Despite many clinical trials over the last two decades since the approval of gemcitabine, the survival of patients with pancreatic cancer has improved by a few only months. This disappointing reality underlines an urgent need to develop more effective drugs or better combinations. A variety of phase I trials were presented at the annual meeting of ASCO 2014 focusing on locally advanced and metastatic pancreatic cancer. We summarize four abstracts (abstracts #4116, #4123, #4026, #4138).

Patterns of care of radiation therapy in patients with stage IV rectal cancer: A Surveillance, Epidemiology, and End Results analysis of patients from 2004 to 2009

According to the 2013 National Comprehensive Cancer Network guidelines, pelvic radiation therapy (RT) is one of the preferred regimens for patients with metastatic rectal cancer (mRC). The objective of this study was to analyze patterns of care and outcomes data for the receipt of RT among patients with mRC using the Surveillance, Epidemiology, and End Results (SEER) database.

Locally Advanced Pancreatic Cancer

Treatment of locally advanced pancreatic cancer is palliative, based on chemotherapy and according to response, chemoradiotherapy can be applied. The authors summarize three abstracts (#LBA146, #256 and #303) presented on the 2013 ASCO Gastrointestinal Cancers Symposium, which were focused on treatment of locally advanced pancreatic cancer. A discussion is presented about the different chemotherapy or chemoradiotherapy regimens, that move away from gemcitabine-based treatment, and the effort to find less toxic, but efficient therapeutic combinations.

Late complications of radiation therapy for breast cancer: evolution in techniques and risk over time

Radiation therapy in combination with surgery, chemotherapy, and endocrine therapy as indicated, has led to excellent local and distant control of early stage breast cancers. With the majority of these patients surviving long term, mitigating the probability and severity of late toxicities is vital. Radiation to the breast, with or without additional fields for nodal coverage, has the potential to negatively impact long term cosmetic outcome of the treated breast as well as cause rare, but severe, complications due to incidental dosage to the heart, lungs and contralateral breast. The long-term clinical side-effects of breast radiation have been studied extensively. This review aims to discuss the risk of developing late complications following breast radiation and how modern techniques can be used to diminish these risks.