Proton therapy for the management of localized prostate cancer: Long-term clinical outcomes at a comprehensive cancer center

BACKGROUND AND PURPOSE

Proton therapy (PT) has emerged as a standard-of-care treatment option for localized prostate cancer at our comprehensive cancer center. However, there are few large-scale analyses examining the long-term clinical outcomes. Therefore, this article aims to evaluate the long-term effectiveness and toxicity of PT in patients with localized prostate cancer.

MATERIALS AND METHODS

Review of 2772 patients treated from May 2006 through January 2020. Disease risk was stratified according to National Comprehensive Cancer Network guidelines as low [LR, n = 640]; favorable-intermediate [F-IR, n = 850]; unfavorable-intermediate [U-IR, n = 851]; high [HR, n = 315]; or very high [VHR, n = 116]. Biochemical failure and toxicity were analyzed using Kaplan-Meier estimates and multivariate models.

RESULTS

The median patient age was 66 years; the median follow-up time was 7.0 years. Pelvic lymph node irradiation was prescribed to 28 patients (1%) (2 [0.2%] U-IR, 11 [3.5%] HR, and 15 [12.9%] VHR). The median dose was 78 Gy in 1.8-2.0 Gy(RBE) fractions. Freedom from biochemical relapse (FFBR) rates at 5 years and 10 years were 98.2% and 96.8% for the LR group; 98.3% and 93.6%, F-IR; 94.2% and 90.2%, U-IR; 94.3% and 85.2%, HR; and 86.1% and 68.5%, VHR. Two patients died of prostate cancer. Overall rates of late grade ≥ 3 GU and GI toxicity were 0.87% and 1.01%.

CONCLUSIONS

Proton therapy for localized prostate cancer demonstrated excellent clinical outcomes in this large cohort, even among higher-risk groups with historically poor outcomes despite aggressive therapy.

Uncertainty in magnetic resonance imaging-based prostate postimplant dosimetry: Results of a 10-person human observer study, and comparisons with automatic postimplant dosimetry

PURPOSE

Uncertainties in postimplant quality assessment (QA) for low-dose-rate prostate brachytherapy (LDRPBT) are introduced at two steps: seed localization and contouring. We quantified how interobserver variability (IoV) introduced in both steps impacts dose-volume-histogram (DVH) parameters for MRI-based LDRPBT, and compared it with automatically derived DVH parameters.

METHODS AND MATERIALS

Twenty-five patients received MRI-based LDRPBT. Seven clinical observers contoured the prostate and four organs at risk, and 4 dosimetrists performed seed localization, on each MRI. Twenty-eight unique manual postimplant QAs were created for each patient from unique observer pairs. Reference QA and automatic QA were also performed for each patient. IoV of prostate, rectum, and external urinary sphincter (EUS) DVH parameters owing to seed localization and contouring was quantified with coefficients of variation. Automatically derived DVH parameters were compared with those of the reference plans.

RESULTS

Coefficients of variation (CoVs) owing to contouring variability (CoVcontours) were significantly higher than those due to seed localization variability (CoVseeds) (median CoVcontours vs. median CoVseeds: prostate D90-15.12% vs. 0.65%, p < 0.001; prostate V100-5.36% vs. 0.37%, p < 0.001; rectum V100-79.23% vs. 8.69%, p < 0.001; EUS V200-107.74% vs. 21.18%, p < 0.001). CoVcontours were lower when the contouring observers were restricted to the 3 radiation oncologists, but were still markedly higher than CoVseeds. Median differences in prostate D90, prostate V100, rectum V100, and EUS V200 between automatically computed and reference dosimetry parameters were 3.16%, 1.63%, -0.00 mL, and -0.00 mL, respectively.

CONCLUSIONS

Seed localization introduces substantially less variability in postimplant QA than does contouring for MRI-based LDRPBT. While automatic seed localization may potentially help improve workflow efficiency, it has limited potential for improving the consistency and quality of postimplant dosimetry.

p16 Represses DNA Damage Repair via a Novel Ubiquitin-Dependent Signaling Cascade

Squamous cell carcinoma driven by human papillomavirus (HPV) is more sensitive to DNA-damaging therapies than its HPV-negative counterpart. Here, we show that p16, the clinically used surrogate for HPV positivity, renders cells more sensitive to radiotherapy via a ubiquitin-dependent signaling pathway, linking high levels of this protein to increased activity of the transcription factor SP1, increased HUWE1 transcription, and degradation of ubiquitin-specific protease 7 (USP7) and TRIP12. Activation of this pathway in HPV-positive disease led to decreased homologous recombination and improved response to radiotherapy, a phenomenon that can be recapitulated in HPV-negative disease using USP7 inhibitors in clinical development. This p16-driven axis induced sensitivity to PARP inhibition and potentially leads to "BRCAness" in head and neck squamous cell carcinoma (HNSCC) cells. Thus, these findings support a functional role for p16 in HPV-positive tumors in driving response to DNA damage, which can be exploited to improve outcomes in both patients with HPV-positive and HPV-negative HNSCC.

SIGNIFICANCE

In HPV-positive tumors, a previously undiscovered pathway directly links p16 to DNA damage repair and sensitivity to radiotherapy via a clinically relevant and pharmacologically targetable ubiquitin-mediated degradation pathway.

Prospective Evaluation of Prostate and Organs at Risk Segmentation Software for MRI-based Prostate Radiation Therapy

The segmentation of the prostate and surrounding organs at risk (OARs) is a necessary workflow step for performing dose-volume histogram analyses of prostate radiation therapy procedures. Low-dose-rate prostate brachytherapy (LDRPBT) is a curative prostate radiation therapy treatment that delivers a single fraction of radiation over a period of days. Prior studies have demonstrated the feasibility of fully convolutional networks to segment the prostate and surrounding OARs for LDRPBT dose-volume histogram analyses. However, performance evaluations have been limited to measures of global similarity between algorithm predictions and a reference. To date, the clinical use of automatic segmentation algorithms for LDRPBT has not been evaluated, to the authors' knowledge. The purpose of this work was to assess the performance of fully convolutional networks for prostate and OAR delineation on a prospectively identified cohort of patients who underwent LDRPBT by using clinically relevant metrics. Thirty patients underwent LDRPBT and were imaged with fully balanced steady-state free precession MRI after implantation. Custom automatic segmentation software was used to segment the prostate and four OARs. Dose-volume histogram analyses were performed by using both the original automatically generated contours and the physician-refined contours. Dosimetry parameters of the prostate, external urinary sphincter, and rectum were compared without and with the physician refinements. This study observed that physician refinements to the automatic contours did not significantly affect dosimetry parameters. Keywords: MRI, Neural Networks, Radiation Therapy, Radiation Therapy/Oncology, Genital/Reproductive, Prostate, Segmentation, Dosimetry Supplemental material is available for this article. © RSNA, 2022.

Computer-aided segmentation on MRI for prostate radiotherapy, part II: Comparing human and computer observer populations and the influence of annotator variability on algorithm variability

BACKGROUND AND PURPOSE

Comparing deep learning (DL) algorithms to human interobserver variability, one of the largest sources of noise in human-performed annotations, is necessary to inform the clinical application, use, and quality assurance of DL for prostate radiotherapy.

MATERIALS AND METHODS

One hundred fourteen DL algorithms were developed on 295 prostate MRIs to segment the prostate, external urinary sphincter (EUS), seminal vesicles (SV), rectum, and bladder. Fifty prostate MRIs of 25 patients undergoing MRI-based low-dose-rate prostate brachytherapy were acquired as an independent test set. Groups of DL algorithms were created based on the loss functions used to train them, and the spatial entropy (SE) of their predictions on the 50 test MRIs was computed. Five human observers contoured the 50 test MRIs, and SE maps of their contours were compared with those of the groups of the DL algorithms. Additionally, similarity metrics were computed between DL algorithm predictions and consensus annotations of the 5 human observers' contours of the 50 test MRIs.

RESULTS

A DL algorithm yielded statistically significantly higher similarity metrics for the prostate than did the human observers (H) (prostate Matthew's correlation coefficient, DL vs. H: planning-0.931 vs. 0.903, p < 0.001; postimplant-0.925 vs. 0.892, p < 0.001); the same was true for the 4 organs at risk. The SE maps revealed that the DL algorithms and human annotators were most variable in similar anatomical regions: the prostate-EUS, prostate-SV, prostate-rectum, and prostate-bladder junctions.

CONCLUSIONS

Annotation quality is an important consideration when developing, evaluating, and using DL algorithms clinically.

Computer-aided segmentation on MRI for prostate radiotherapy, Part I: Quantifying human interobserver variability of the prostate and organs at risk and its impact on radiation dosimetry

BACKGROUND AND PURPOSE

Quantifying the interobserver variability (IoV) of prostate and periprostatic anatomy delineation on prostate MRI is necessary to inform its use for treatment planning, treatment delivery, and treatment quality assessment.

MATERIALS AND METHODS

Twenty five prostate cancer patients underwent MRI-based low-dose-rate prostate brachytherapy (LDRPBT). The patients were scanned with a 3D T2-weighted sequence for treatment planning and a 3D T2/T1-weighted sequence for quality assessment. Seven observers involved with the LDRPBT workflow delineated the prostate, external urinary sphincter (EUS), seminal vesicles, rectum, and bladder on all 50 MRIs. IoV was assessed by measuring contour similarity metrics, differences in organ volumes, and differences in dosimetry parameters between unique observer pairs. Measurements from a group of 3 radiation oncologists (G1) were compared against those from a group consisting of the other 4 clinical observers (G2).

RESULTS

IoV of the prostate was lower for G1 than G2 (Matthew's correlation coefficient [MCC], G1 vs. G2: planning-0.906 vs. 0.870, p < 0.001; postimplant-0.899 vs. 0.861, p < 0.001). IoV of the EUS was highest of all the organs for both groups, but was lower for G1 (MCC, G1 vs. G2: planning-0.659 vs. 0.402, p < 0.001; postimplant-0.684 vs. 0.398, p < 0.001). Large differences in prostate dosimetry parameters were observed (G1 maximum absolute prostate ΔD90: planning-76.223 Gy, postimplant-36.545 Gy; G1 maximum absolute prostate ΔV100: planning-13.927%, postimplant-8.860%).

CONCLUSIONS

While MRI is optimal in the management of prostate cancer with radiation therapy, significant interobserver variability of the prostate and external urinary sphincter still exist.

Sample-size calculation for preclinical dose-response experiments using heterogeneous tumour models

BACKGROUND

In preclinical radio-oncological research, local tumour control is considered the most relevant endpoint as it reflects the inactivation of cancer stem cells. Preclinical tumour-control assays may compare dose-response curves between different radiotherapy strategies, e.g., assessing additional targeted drugs and immunotherapeutic interventions, or between different radiation modalities. To mimic the biological heterogeneity of human tumour populations and to accommodate for approaches of personalized oncology, preclinical studies are increasingly performed combining larger panels of tumour models. For designing the study protocols and to obtain reliable results, prospective sample-size planning has to be developed that accounts for such heterogeneous cohorts.

METHODS

A Monte-Carlo-based method was developed to estimate the sample size of a comparative 1:1 two-arm prospective tumour-control assay. Based on repeated logistic regression analysis, pre-defined dose levels, assumptions on the dose-response curves of the included tumour models and on the dose-modifying factors (DMF), the power is calculated for a given number of animals per dose group.

RESULTS

Two applications are presented: (i) For a simple tumour-control assay with the head and neck squamous cell carcinoma (HNSCC) model FaDu, 10 animals would be required for each of 7 dose levels per arm to reveal a DMF of 1.25 with a power of 0.82 without drop out (total: 140 animals). (ii) In a more complex experiment combining six different lung tumour models to a heterogeneous population, 21 animals would be required for each of 11 dose levels per arm to reveal a DMF of 1.25 with a power of 0.81 without drop out (total: 462 animals). Analyzing the heterogeneous cohort reduces the required animal number by more than 50% compared to six individual tumour-control assays.

CONCLUSION

An approach for estimating the required animal number for comparative tumour-control assays in a heterogeneous population is presented, allowing also the inclusion of different treatments as a personalized approach in the experimental arm. The software is publicly available and can be applied to plan comparisons of sigmoidal dose-response curves based on logistic regression.

The Withers archive: Online availability of rod Wither's data

The contents of the lab notebooks of H.R. Withers have been digitized and stored as 23 excel files, a total of approximately 45 megabytes. A procedure is described whereby those interested may gain access to the data.

The Limitations of Model-Based Experimental Design and Parameter Estimation in Sloppy Systems

We explore the relationship among experimental design, parameter estimation, and systematic error in sloppy models. We show that the approximate nature of mathematical models poses challenges for experimental design in sloppy models. In many models of complex biological processes it is unknown what are the relevant physical mechanisms that must be included to explain system behaviors. As a consequence, models are often overly complex, with many practically unidentifiable parameters. Furthermore, which mechanisms are relevant/irrelevant vary among experiments. By selecting complementary experiments, experimental design may inadvertently make details that were ommitted from the model become relevant. When this occurs, the model will have a large systematic error and fail to give a good fit to the data. We use a simple hyper-model of model error to quantify a model’s discrepancy and apply it to two models of complex biological processes (EGFR signaling and DNA repair) with optimally selected experiments. We find that although parameters may be accurately estimated, the discrepancy in the model renders it less predictive than it was in the sloppy regime where systematic error is small. We introduce the concept of a sloppy system–a sequence of models of increasing complexity that become sloppy in the limit of microscopic accuracy. We explore the limits of accurate parameter estimation in sloppy systems and argue that identifying underlying mechanisms controlling system behavior is better approached by considering a hierarchy of models of varying detail rather than focusing on parameter estimation in a single model.

Sloppy models are often unidentifiable, i.e., characterized by many parameters that are poorly constrained by experimental data. Many models of complex biological systems are sloppy, which has prompted considerable debate about the identifiability of parameters and methods of selecting optimal experiments to infer parameter values. We explore how the approximate nature of models affects the prospect for accurate parameter estimates and model predictivity in sloppy models when using optimal experimental design. We find that sloppy models may no longer give a good fit to data generated from “optimal” experiments. In this case, the model has much less predictive power than it did before optimal experimental selection. We use a simple hyper-model of model error to quantify the model’s discrepancy from the physical system and discuss the potential limits of accurate parameter estimation in sloppy systems.

HPV status, cancer stem cell marker expression, hypoxia gene signatures and tumour volume identify good prognosis subgroups in patients with HNSCC after primary radiochemotherapy: A multicentre retrospective study of the German Cancer Consortium Radiation Oncology Group (DKTK-ROG)

OBJECTIVE

To investigate the impact of the tumour volume, HPV status, cancer stem cell (CSC) marker expression and hypoxia gene signatures, as potential markers of radiobiological mechanisms of radioresistance, in a contemporary cohort of patients with locally advanced head and neck squamous cell carcinoma (HNSCC), who received primary radiochemotherapy (RCTx).

MATERIALS AND METHODS

For 158 patients with locally advanced HNSCC of the oral cavity, oropharynx or hypopharynx who were treated at six DKTK partner sites, the impact of tumour volume, HPV DNA, p16 overexpression, p53 expression, CSC marker expression and hypoxia-associated gene signatures on outcome of primary RCTx was retrospectively analyzed. The primary endpoint of this study was loco-regional control (LRC).

RESULTS

Univariate Cox regression revealed a significant impact of tumour volume, p16 overexpression, and SLC3A2 and CD44 protein expression on LRC. The tumour hypoxia classification showed a significant impact only for small tumours. In multivariate analyses an independent correlation of tumour volume, SLC3A2 expression, and the 15-gene hypoxia signature with LRC was identified (CD44 protein n/a because of no event in the CD44-negative group). Logistic modelling showed that inclusion of CD44 protein expression and p16 overexpression significantly improved the performance to predict LRC at 2years compared to the model with tumour volume alone.

CONCLUSIONS

Tumour volume, HPV status, CSC marker expression and hypoxia gene signatures are potential prognostic biomarkers for patients with locally advanced HNSCC, who were treated by primary RCTx. The study also supports that the individual tumour volumes should generally be included in biomarker studies and that panels of biomarkers are superior to individual parameters.

The Withers Archive: online availability of H. Rodney Withers' data

We have collected lab notebooks from Rod Wither's many years of experimentation, from laboratories in Houston and Los Angeles, as well as from several of his collaborators in the USA and overseas. The contents have been digitized, and in this note we explain the mechanism that has been set up to make the 'Withers Archive' available online.

Lower mean heart dose with deep inspiration breath hold-whole breast irradiation compared with brachytherapy-based accelerated partial breast irradiation for women with left-sided tumors

PURPOSE

For left-sided breast cancer, radiation to the heart is a concern. We present a comparison of mean heart and coronary artery biologically effective dose (BED) between accelerated partial breast irradiation (APBI) and whole breast irradiation with deep inspiration breath-hold technique (DIBH-WBI).

METHODS AND MATERIALS

A total of 100 patients with left-sided, early-stage breast cancer were identified. Fifty underwent single-entry catheter-based APBI and 50 underwent DIBH-WBI. The heart, left anterior descending/interventricular branch, left main, and right coronary artery were delineated. BEDs were calculated from APBI treatment plans (34 Gy in 3.4 Gy twice daily fractions) and for 4 separate plans generated for each DIBH-WBI patient: 50 Gy in 25 fractions (50/25), 50/25 + 10/5 boost, 40/15, and 40/15 + 10/5 boost.

RESULTS

BED to the heart and coronary vessels were statistically significantly higher with APBI than with any of the DIBH-WBI dose/fractionation schedules.

CONCLUSIONS

For women with left-sided early-stage breast cancer, DIBH-WBI resulted in statistically significantly lower mean BED to the heart and coronary vessels compared with APBI. This is likely due to increased physical separation between the heart and tumor bed afforded by the DIBH-WBI technique. Long-term assessment of late effects in these tissues will be required to determine whether these differences are clinically significant.

TRIP12 as a mediator of human papillomavirus/p16-related radiation enhancement effects

Patients with human papillomavirus (HPV)-positive head and neck squamous cell carcinoma (HNSCC) have better responses to radiotherapy and higher overall survival rates than do patients with HPV-negative HNSCC, but the mechanisms underlying this phenomenon are unknown. p16 is used as a surrogate marker for HPV infection. Our goal was to examine the role of p16 in HPV-related favorable treatment outcomes and to investigate the mechanisms by which p16 may regulate radiosensitivity. HNSCC cells and xenografts (HPV/p16-positive and -negative) were used. p16-overexpressing and small hairpin RNA-knockdown cells were generated, and the effect of p16 on radiosensitivity was determined by clonogenic cell survival and tumor growth delay assays. DNA double-strand breaks (DSBs) were assessed by immunofluorescence analysis of 53BP1 foci; DSB levels were determined by neutral comet assay; western blotting was used to evaluate protein changes; changes in protein half-life were tested with a cycloheximide assay; gene expression was examined by real-time polymerase chain reaction; and data from The Cancer Genome Atlas HNSCC project were analyzed. p16 overexpression led to downregulation of TRIP12, which in turn led to increased RNF168 levels, repressed DNA damage repair (DDR), increased 53BP1 foci and enhanced radioresponsiveness. Inhibition of TRIP12 expression further led to radiosensitization, and overexpression of TRIP12 was associated with poor survival in patients with HPV-positive HNSCC. These findings reveal that p16 participates in radiosensitization through influencing DDR and support the rationale of blocking TRIP12 to improve radiotherapy outcomes.

Computational Modeling of Micrometastatic Breast Cancer Radiation Dose Response

PURPOSE

Prophylactic cranial irradiation (PCI) involves giving radiation to the entire brain with the goals of reducing the incidence of brain metastasis and improving overall survival. Experimentally, we have demonstrated that PCI prevents brain metastases in a breast cancer mouse model. We developed a computational model to expand on and aid in the interpretation of our experimental results.

METHODS AND MATERIALS

MATLAB was used to develop a computational model of brain metastasis and PCI in mice. Model input parameters were optimized such that the model output would match the experimental number of metastases per mouse from the unirradiated group. An independent in vivo-limiting dilution experiment was performed to validate the model. The effect of whole brain irradiation at different measurement points after tumor cells were injected was evaluated in terms of the incidence, number of metastases, and tumor burden and was then compared with the corresponding experimental data.

RESULTS

In the optimized model, the correlation between the number of metastases per mouse and the experimental fits was >95. Our attempt to validate the model with a limiting dilution assay produced 99.9% correlation with respect to the incidence of metastases. The model accurately predicted the effect of whole-brain irradiation given 3 weeks after cell injection but substantially underestimated its effect when delivered 5 days after cell injection. The model further demonstrated that delaying whole-brain irradiation until the development of gross disease introduces a dose threshold that must be reached before a reduction in incidence can be realized.

CONCLUSIONS

Our computational model of mouse brain metastasis and PCI correlated strongly with our experiments with unirradiated mice. The results further suggest that early treatment of subclinical disease is more effective than irradiating established disease.

Splenic radiation during pancreatic cancer radiotherapy: Are we throwing the baby out with the bath water?

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Background: Lymphopenia is commonly seen following chemoradiation and is associated with a poor prognosis. We conducted this study to determine if the severity of lymphopenia is dependent on the radiation dose and the fractional volume of spleen irradiated unintentionally during definitive chemoradiation in patients with locally advanced pancreatic cancer (LAPC). Methods: 177 patients with LAPC were treated with induction chemotherapy (FOLFIRINOX or gemcitabine- based regimens) followed by chemoradiation (CRT; median 50.4 Gy with concurrent capecitabine) from 1/2006 to 12/2012. Absolute lymphocyte count (ALC) was recorded at baseline, prior to CRT and 2-10 weeks after the end of CRT. Splenic dose-volume histogram (DVH) parameters were reported as mean splenic dose (MSD) and the percentage of splenic volume receiving at least 5 Gy (V5), 10 Gy (V10), 15 Gy (V15) and 20 Gy (V20) dose. Overall survival (OS) was analyzed using Cox model and multivariate logistic regression was used to assess the development of post CRT severe lymphopenia (ALC < 0.5 K/UL) using baseline and treatment factors. Results: Median post-CRT ALC (0.68 K/UL, range 0.13 to 2.72) was significantly lower than both baseline (1.42 K/UL, range 0.34- 3.97; p < 0.0001) and pre-CRT ALC (1.32 K/UL, range 0.36- 4.82; p < 0.0001). Post-CRT ALC < 0.5 K/UL was associated with inferior OS on univariate (16.8 vs. 21.2 months, p = 0.004) and multivariate analysis (HR = 1.9, p = 0.002).The MSD was 8.8 Gy and log MSD showed a significant negative correlation (r = -0.18, p = 0.02) with post-CRT ALC. Median V5, V10, V15 and V20 were 34%, 21%, 13% and 8% respectively. Median V10 (32.6 vs. 16%, p = 0.04), V15 (23.2 vs. 9.5%, p = 0.03) and V20 (15.4 vs. 4.6%, p = 0.02) were significantly higher in patients with severe lymphopenia. On multivariate logistic regression analysis, baseline lymphopenia (ALC < 1 K/UL; p = 0.003, OR = 4.6) and MSD (p = 0.03, OR = 7.3) were independent predictors for the development of severe post-CRT lymphopenia. Conclusions: LAPC patients receiving high MSD during CRT are at increased risk of developing severe lymphopenia, which is an independent predictor of poor OS. Routine assessment of splenic DVHs prior to acceptance of treatment plans may minimize this risk.

Low Cancer Stem Cell Marker Expression and Low Hypoxia Identify Good Prognosis Subgroups in HPV(-) HNSCC after Postoperative Radiochemotherapy: A Multicenter Study of the DKTK-ROG

PURPOSE

To investigate the impact of hypoxia-induced gene expression and cancer stem cell (CSC) marker expression on outcome of postoperative cisplatin-based radiochemotherapy (PORT-C) in patients with locally advanced head and neck squamous cell carcinoma (HNSCC).

EXPERIMENTAL DESIGN

Expression of the CSC markers CD44, MET, and SLC3A2, and hypoxia gene signatures were analyzed in the resected primary tumors using RT-PCR and nanoString technology in a multicenter retrospective cohort of 195 patients. CD44 protein expression was further analyzed in tissue microarrays. Primary endpoint was locoregional tumor control.

RESULTS

Univariate analysis showed that hypoxia-induced gene expression was significantly associated with a high risk of locoregional recurrence using the 15-gene signature (P = 0.010) or the 26-gene signature (P = 0.002). In multivariate analyses, in patients with HPV16 DNA-negative but not with HPV16 DNA-positive tumors the effect of hypoxia-induced genes on locoregional control was apparent (15-gene signature: HR 4.54, P = 0.006; 26-gene signature: HR 10.27, P = 0.024). Furthermore, MET, SLC3A2, CD44, and CD44 protein showed an association with locoregional tumor control in multivariate analyses (MET: HR 3.71, P = 0.016; SLC3A2: HR 8.54, P = 0.037; CD44: HR 3.36, P = 0.054; CD44 protein n/a because of no event in the CD44-negative group) in the HPV16 DNA-negative subgroup.

CONCLUSIONS

We have shown for the first time that high hypoxia-induced gene expression and high CSC marker expression levels correlate with tumor recurrence after PORT-C in patients with HPV16 DNA-negative HNSCC. After validation in a currently ongoing prospective trial, these parameters may help to further stratify patients for individualized treatment de-escalation or intensification strategies. Clin Cancer Res; 22(11); 2639-49. ©2016 AACR.

Ablative Radiotherapy Doses Lead to a Substantial Prolongation of Survival in Patients With Inoperable Intrahepatic Cholangiocarcinoma: A Retrospective Dose Response Analysis

PURPOSE

Standard therapies for localized inoperable intrahepatic cholangiocarcinoma (IHCC) are ineffective. Advances in radiotherapy (RT) techniques and image guidance have enabled ablative doses to be delivered to large liver tumors. This study evaluated the effects of RT dose escalation in the treatment of IHCC.

PATIENTS AND METHODS

Seventy-nine consecutive patients with inoperable IHCC were identified and treated with definitive RT from 2002 to 2014. At diagnosis, the median tumor size was 7.9 cm (range, 2.2 to 17 cm). Seventy patients (89%) received systemic chemotherapy before RT. RT doses were 35 to 100 Gy (median, 58.05 Gy) in three to 30 fractions for a median biologic equivalent dose (BED) of 80.5 Gy (range, 43.75 to 180 Gy).

RESULTS

Median follow-up time for patients alive at time of analysis was 33 months (range, 11 to 93 months). Median overall survival (OS) time after diagnosis was 30 months; 3-year OS rate was 44%. Radiation dose was the single most important prognostic factor; higher doses correlated with an improved local control (LC) rate and OS. The 3-year OS rate for patients receiving BED greater than 80.5 Gy was 73% versus 38% for those receiving lower doses (P = .017); 3-year LC rate was significantly higher (78%) after a BED greater than 80.5 Gy than after lower doses (45%, P = .04). BED as a continuous variable significantly affected LC (P = .009) and OS (P = .004). There were no significant treatment-related toxicities.

CONCLUSION

Delivery of higher doses of RT improves LC and OS in inoperable IHCC. A BED greater than 80.5 Gy seems to be an ablative dose of RT for large IHCCs, with long-term survival rates that compare favorably with resection.

HPV16 DNA status is a strong prognosticator of loco-regional control after postoperative radiochemotherapy of locally advanced oropharyngeal carcinoma: results from a multicentre explorative study of the German Cancer Consortium Radiation Oncology Group (DKTK-ROG)

OBJECTIVE

To investigate the impact of HPV status in patients with locally advanced head and neck squamous cell carcinoma (HNSCC), who received surgery and cisplatin-based postoperative radiochemotherapy.

MATERIALS AND METHODS

For 221 patients with locally advanced squamous cell carcinoma of the hypopharynx, oropharynx or oral cavity treated at the 8 partner sites of the German Cancer Consortium, the impact of HPV DNA, p16 overexpression and p53 expression on outcome were retrospectively analysed. The primary endpoint was loco-regional tumour control; secondary endpoints were distant metastases and overall survival.

RESULTS

In the total patient population, univariate analyses revealed a significant impact of HPV16 DNA positivity, p16 overexpression, p53 positivity and tumour site on loco-regional tumour control. Multivariate analysis stratified for tumour site showed that positive HPV 16 DNA status correlated with loco-regional tumour control in patients with oropharyngeal carcinoma (p=0.02) but not in the oral cavity carcinoma group. Multivariate evaluation of the secondary endpoints in the total population revealed a significant association of HPV16 DNA positivity with overall survival (p<0.01) but not with distant metastases.

CONCLUSIONS

HPV16 DNA status appears to be a strong prognosticator of loco-regional tumour control after postoperative cisplatin-based radiochemotherapy of locally advanced oropharyngeal carcinoma and is now being explored in a prospective validation trial.

Use of the LQ model with large fraction sizes results in underestimation of isoeffect doses

PURPOSE

To test the appropriateness of the linear-quadratic (LQ) model to describe survival of jejunal crypt clonogens after split doses with variable (small 1-6 Gy, large 8-13 Gy) first dose, as a model of its appropriateness for both small and large fraction sizes.

METHODS

C3Hf/KamLaw mice were exposed to whole body irradiation using 300 kVp X-rays at a dose rate of 1.84 Gy/min, and the number of viable jejunal crypts was determined using the microcolony assay. 14 Gy total dose was split into unequal first and second fractions separated by 4 h. Data were analyzed using the LQ model, the lethal potentially lethal (LPL) model, and a repair-saturation (RS) model.

RESULTS

Cell kill was greater in the group receiving the larger fraction first, creating an asymmetry in the plot of survival vs size of first dose, as opposed to the prediction of the LQ model of a symmetric response. There was a significant difference in the estimated βs (higher β after larger first doses), but no significant difference in the αs, when large doses were given first vs small doses first. This difference results in underestimation (based on present data by approximately 8%) of isoeffect doses using LQ model parameters based on small fraction sizes. While the LPL model also predicted a symmetric response inconsistent with the data, the RS model results were consistent with the observed asymmetry.

CONCLUSION

The LQ model underestimates doses for isoeffective crypt-cell survival with large fraction sizes (in the present setting, >9 Gy).

Prognostic value of HIF-1α expression during fractionated irradiation

BACKGROUND AND PURPOSE

Hypoxia and reoxygenation are important determinants of outcome after radiotherapy. HIF-1α is a key molecule involved in cellular response to hypoxia. HIF-1α expression levels have been shown to change after irradiation. The objective of the present study was to explore the prognostic value of HIF-1α expression during fractionated irradiation.

MATERIALS AND METHODS

Six human squamous cell carcinoma models xenografted in nude mice were analysed. Tumours were excised after 3, 5 and 10 fractions. HIF-1α expression was quantified by western blot. For comparative analysis, previously published data on local tumour control data and pimonidazole hypoxic fraction was used.

RESULTS

HIF-1α expression in untreated tumours exhibited intertumoural heterogeneity and did not correlate with pimonidazole hypoxic fraction. During fractionated irradiation the majority of tumour models exhibited a decrease in HIF-1α expression, whereas in UT-SCC-5 no change was observed. Neither kinetics nor expression levels during fractionated irradiation correlated with local tumour control.

CONCLUSION

Our data do not support the use of HIF-1α determined during treatment as a biomarker to predict outcome after fractionated irradiation.

Estimation of α/β for late rectal toxicity based on RTOG 94-06

PURPOSE

To estimate α/β, the parameter ratio from the linear-quadratic (LQ) model, for Grade ≥2 late rectal toxicity among patients treated on Radiation Therapy Oncology Group (RTOG) protocol 94-06; and to determine whether correcting the rectal dose-volume histogram (DVH) for differences in dose per fraction, based on the LQ model, significantly improves the fit to these data of the Lyman-Kutcher-Burman (LKB) normal-tissue complication probability (NTCP) model.

METHODS AND MATERIALS

The generalized LKB model was fitted to the Grade ≥2 late rectal toxicity data in two ways: by using DVHs representing physical dose to rectum, and by using a modified approach in which dose bins in the rectal DVH were corrected for differences in dose per fraction using the LQ model, with α/β estimated as an additional unknown parameter. The analysis included only patients treated with the same treatment plan throughout radiotherapy, so that the dose per fraction to each voxel of rectum could be determined from the DVH. The likelihood ratio test was used to assess whether the fit of the LQ-corrected model was significantly better than the fit of the LKB model based on physical doses to rectum.

RESULTS

The analysis included 509 of the 1,084 patients enrolled on RTOG 94-06. The estimate of α/β from the LQ-corrected LKB model was 4.8 Gy, with 68% confidence interval 0.6 Gy to 46 Gy. The fit was not significantly different from the fit of the LKB model based on physical dose to rectum (p = 0.236).

CONCLUSIONS

The estimated fractionation sensitivity for Grade ≥2 late rectal toxicity is consistent with values of α/β for rectum found previously in human beings and in rodents. However, the confidence interval is large, and there is no evidence that LQ correction of the rectal DVH significantly changes the fit or predictions of the LKB model for this endpoint.

Late rectal toxicity on RTOG 94-06: analysis using a mixture Lyman model

PURPOSE

To estimate the parameters of the Lyman normal-tissue complication probability model using censored time-to-event data for Grade ≥2 late rectal toxicity among patients treated on Radiation Therapy Oncology Group 94-06, a dose-escalation trial designed to determine the maximum tolerated dose for three-dimensional conformal radiotherapy of prostate cancer.

METHODS AND MATERIALS

The Lyman normal-tissue complication probability model was fitted to data from 1,010 of the 1,084 patients accrued on Radiation Therapy Oncology Group 94-06 using an approach that accounts for censored observations. Separate fits were obtained using dose-volume histograms for whole rectum and dose-wall histograms for rectal wall.

RESULTS

With a median follow-up of 7.2 years, the crude incidence of Grade ≥2 late rectal toxicity was 15% (n = 148). The parameters of the Lyman model fitted to dose-volume histograms data, with 95% profile-likelihood confidence intervals, were TD(50) = 79.1 Gy (75.3 Gy, 84.3 Gy), m = 0.146 (0.107, 0.225), and n = 0.077 (0.041, 0.156). The fit based on dose-wall histogram data was not significantly different. Patients with cardiovascular disease had a significantly higher incidence of late rectal toxicity (p = 0.015), corresponding to a dose-modifying factor of 5.3%. No significant association with late rectal toxicity was found for diabetes, hypertension, rectal volume, rectal length, neoadjuvant hormone therapy, or prescribed dose per fraction (1.8 Gy vs. 2 Gy).

CONCLUSIONS

These results, based on a large cohort of patients from a multi-institutional trial, are expected to be widely representative of the ability of the Lyman model to describe the long-term risk of Grade ≥2 late rectal toxicity after three-dimensional conformal radiotherapy of prostate cancer.

Detoxication of sulfur half-mustards by nucleophilic scavengers: robust activity of thiopurines

Sulfur mustard (bis-(2-chloroethyl)sulfide) has been used in chemical warfare since World War I and is well known as an acutely toxic vesicant. It has been implicated as a carcinogen after chronic low-level exposure and is known to form interstrand cross-links in DNA. Sulfur and nitrogen mustards are currently of interest as potential chemical threat agents for terrorists because of ease of synthesis. Sulfur mustard and monofunctional analogues (half-mustards, 2-[chloroethyl] alkyl sulfides) react as electrophiles, damaging cellular macromolecules, and thus are potentially subject to scavenging by nucleophilic agents. We have determined rate constants for the reaction of four purine derivatives that contain nucleophilic thiol moieties with several sulfur-half-mustards. Three of these compounds, 2,6-dithiopurine, 2,6-dithiouric acid, and 9-methyl-6-mercaptopurine, exhibit facile reaction with the electrophilic mustard compounds. At near neutral pH, these thiopurines are much better nucleophilic scavengers of mustard electrophiles than other low molecular weight thiols such as N-acetyl cysteine and glutathione. Progress curves calculated by numerical integration techniques indicate that equimolar concentrations of thiopurine provide significant reductions in the overall exposure to the episulfonium ions, which are the major reactive, electrophiles produced when sulfur mustards are dissolved in aqueous solution.

Prediction of clonogenic cell survival curves based on the number of residual DNA double strand breaks measured by gammaH2AX staining

PURPOSE

To assess the potential of using the residual phosphorylation of histone H2AX (gammaH2AX) after irradiation as a marker of radiosensitivity in vitro.

MATERIAL AND METHODS

Confluent cell cultures of FaDu and SKX human squamous cell carcinoma lines were irradiated with graded single doses. Twenty-four hours after irradiation cells were seeded for standard colony forming assay (CFA). In parallel, staining for gammaH2AX was performed to visualise the residual foci.

RESULTS

In the CFA, FaDu showed a higher radioresistance than SKX. After analysis of the residual foci data, we constructed 'predicted' survival curves using two different methods. First, the proportion of nuclei with <3 foci was found to correlate closely with the observed surviving fraction (SF) in FaDu, with a slight overestimation of the true SF in SKX. Second, there was a strong linear correlation of the mean number of residual foci and observed -lnSF. Based on regression analysis, we calculated the SF for both cell lines based on the mean number of residual gammaH2AX foci. This second approach again led to a good correlation of predicted and observed SF values in FaDu and a (slight) overestimation in SKX.

CONCLUSION

In the two cell lines investigated the mean number of residual foci of gammaH2AX can be used to predict differences in the radiation dose response relationship in vitro.

Concurrent chemoradiation in the routine management of patients with cervical cancer: does marital status matter?

OBJECTIVE

The aim of this study was to investigate the relationship between marital status and outcome in women treated with concurrent chemoradiation (CT-RT) for locally advanced cervical cancer.

METHODS

We reviewed the records of all women who received CT-RT for squamous or adenocarcinomas of the cervix at the M. D. Anderson Cancer Center between 1998 and 2005. Patients with extrapelvic disease, prior hysterectomy, concurrent second malignancies, or prior pelvic radiation therapy or chemotherapy were excluded. All patients received external beam and intracavitary radiation therapy with concurrent weekly cisplatin or cisplatin and 5-fluorouracil. Of 226 women, 117 were married (MPs; median follow-up, 41 months) and 109 were single, divorced, or separated (SPs; median follow-up, 42 months).

RESULTS

The SPs were more likely to be African American (P < 0.001), be medically indigent (P < 0.001), and have used illicit drugs (P = 0.01). Married patients were more likely to have traveled to Houston for care; SPs were more likely to be permanent residents of Houston (61% vs 29.1%, P < 0.001). The SPs more often presented with tumors of 6.0 cm or more (P = 0.01) and stage II to IVA disease (P = 0.02). There were no other significant between-group differences in patient or tumor characteristics or CT-RT compliance. At 3 years, there were no significant between-group differences in disease-specific (80% in MPs vs 78% in SPs, P = 0.61) or pelvic relapse-free survival rates (88% in MPs vs 86% in SPs, P = 0.62).

CONCLUSIONS

Despite patient and tumor characteristics traditionally associated with poorer outcomes, SPs do not have significantly poorer treatment completion rates or outcomes after CT-RT. Further studies are needed to determine whether these trends hold true in other practice settings.

Impact of increased cell loss on the repopulation rate during fractionated irradiation in human FaDu squamous cell carcinoma growing in nude mice

PURPOSE

To determine the impact of increased necrotic cell loss on the repopulation rate of clonogenic cells during fractionated irradiation in human FaDu squamous cell carcinoma in nude mice.

MATERIALS AND METHODS

FaDu tumours were transplanted into pre-irradiated subcutaneous tissues. This manoeuvre has previously been shown to result in a clear-cut tumour bed effect, i.e. tumours grow at a slower rate compared with control tumours. This tumour bed effect was caused by an increased necrotic cell loss with a constant cell production rate. After increasing numbers of 3-Gy fractions (time intervals 24 or 48 h), graded top-up doses were given to determine the dose required to control 50% of the tumours (TCD50). All irradiations were given under clamp hypoxia.

RESULTS

With increasing numbers of daily fractions, the top-up TCD50 decreased from 37.9 Gy (95% CI: 31; 45) after single dose irradiation to 14.1 Gy (8; 20) after irradiation with 15 fractions in 15 days. Irradiation with 18 daily 3-Gy fractions controlled more than 50% of the tumours without a top-up dose. After irradiation with six fractions every second day, the top-up TCD50 decreased to 26.9 Gy (22; 32). No further decrease of the TCD50 was observed after 12 and 18 irradiations every second day. Assuming a constant increase of TCD50 with time, the calculated doubling time of the clonogenic tumour cells (Tclon) was 7.8 days (4.4; 11.3). The Tclon calculated for FaDu tumours growing in pre-irradiated tissues was significantly longer (p=0.0004) than the Tclon of 5.1 days (3.7; 6.5) determined under the same assumptions in a previous study for FaDu tumours growing in normal subcutaneous tissues.

CONCLUSIONS

Increased necrotic cell loss by pre-irradiation of the tumour bed resulted in longer clonogen doubling times during fractionated radiotherapy of human FaDu squamous cell carcinoma. This implies that a decreased necrotic cell loss might be the link between reoxygenation and repopulation demonstrated previously in the same tumour model.

Differentiation status of human squamous cell carcinoma xenografts does not appear to correlate with the repopulation capacity of clonogenic tumour cells during fractionated irradiation

PURPOSE

To investigate the magnitude and kinetics of repopulation in a moderately well differentiated UT-SCC-14 human squamous cell carcinoma [hSCC] in nude mice. This question is of interest because clinical data indicate a higher repopulation capacity in those SCC that have preserved characteristics of differentiation, which appears to be in contrast to results on FaDu and GL hSCC previously reported from this laboratory.

METHODS AND MATERIALS

UT-SCC-14 tumours were transplanted subcutaneously into the right hind leg of NMRI nu/nu mice. Fractionated radiation treatments were delivered, either under clamped hypoxia at 5.4 Gy/fraction or under ambient conditions (consistent with an OER of 2.7). Tumours were irradiated every day, every 2nd day, or every 3rd day with 6, 12 or 18 fractions. 1, 2 or 3 days after the last fraction, graded top-up-doses under clamped conditions were given for the purpose of estimating the 50% tumour control dose (TCD50). A total of 22 TCD50 assays were performed and analysed using maximum likelihood techniques.

RESULTS

The data demonstrate a slow but significant repopulation of clonogenic cells during fractionated irradiation of UT-SCC-14 hSCC. The results under hypoxic conditions are consistent with a constant repopulation rate, with a clonogenic doubling time (Tclon) of 15.6 days (95% CI: 9.7, 21.4). This contrasts with ambient conditions where Tclon was 68.5 days (95% CI: 124, 161). Both Tclon values are longer than the 6-day volume doubling time of untreated tumours.

CONCLUSIONS

Less pronounced repopulation for irradiation under ambient compared to clamped hypoxic conditions might be explained by preferential survival of hypoxic and therefore non-proliferating clonogenic cells. Taken together with previous studies on poorly differentiated FaDu and moderately well differentiated GL hSCC, the results are consistent with considerable variability in the magnitude and kinetics of repopulation in different experimental squamous cell carcinomas, and with a relationship between reoxygenation and repopulation during fractionated irradiation. The differentiation status of hSCC growing in nude mice does not to appear to correlate with the proliferative capacity of clonogenic tumour cells during treatment. The results do not support the hypothesis gained from clinical data of higher repopulation in well-differentiated tumours.

Dual radiobiological interpretations of retrospective clinical data: the time factor

Dual interpretations are different radiobiological mechanisms that explain theoretically the same observed results. Radiobiological interpretations of the time factor are most frequently based on changes in total dose that produce a given effect. If this dose is increased by different mechanisms (e.g. increasing overall time and decreasing dose per fraction) at the same time, proposals for altered fractionation schemes based on the choice of one or the other mechanism, in principle, can lead to erroneous predictions of outcome. This is especially the case when the analyses are based on retrospective clinical data, where the influence of patient selection is unknown. Examples of dual interpretations taken from the literature on head and neck, melanoma and prostate cancer are discussed.

Influence of technologic advances on outcomes in patients with unresectable, locally advanced non-small-cell lung cancer receiving concomitant chemoradiotherapy

PURPOSE

In 2004, our institution began using four-dimensional computed tomography (4DCT) simulation and then intensity-modulated radiotherapy (IMRT) (4DCT/IMRT) instead of three-dimensional conformal radiotherapy (3DCRT) for the standard treatment of non-small-cell lung cancer (NSCLC). This retrospective study compares disease outcomes and toxicity in patients treated with concomitant chemotherapy and either 4DCT/IMRT or 3DCRT.

METHODS AND MATERIALS

A total of 496 NSCLC patients have been treated at M. D. Anderson Cancer Center between 1999 and 2006 with concomitant chemoradiotherapy. Among these, 318 were treated with CT/3DCRT and 91 with 4DCT/IMRT. Both groups received a median dose of 63 Gy. Disease end points were locoregional progression (LRP), distant metastasis (DM), and overall survival (OS). Disease covariates were gross tumor volume (GTV), nodal status, and histology. The toxicity end point was Grade >or=3 radiation pneumonitis; toxicity covariates were GTV, smoking status, and dosimetric factors. Data were analyzed using Cox proportional hazards models.

RESULTS

Mean follow-up times in the 4DCT/IMRT and CT/3DCRT groups were 1.3 (range, 0.1-3.2) and 2.1 (range, 0.1-7.9) years, respectively. The hazard ratios for 4DCT/IMRT were <1 for all disease end points; the difference was significant only for OS. The toxicity rate was significantly lower in the IMRT/4DCT group than in the CT/3DCRT group. V20 was significantly higher in the 3DCRT group and was a significant factor in determining toxicity. Freedom from DM was nearly identical in both groups.

CONCLUSIONS

Treatment with 4DCT/IMRT was at least as good as that with 3DCRT in terms of the rates of freedom from LRP and DM. There was a significant reduction in toxicity and a significant improvement in OS.

The transcription factor ATF3 acts as an oncogene in mouse mammary tumorigenesis

Background

Overexpression of the bZip transcription factor, ATF3, in basal epithelial cells of transgenic mice under the control of the bovine cytokeratin-5 (CK5) promoter has previously been shown to induce epidermal hyperplasia, hair follicle anomalies and neoplastic lesions of the oral mucosa including squamous cell carcinomas. CK5 is known to be expressed in myoepithelial cells of the mammary gland, suggesting the possibility that transgenic BK5.ATF3 mice may exhibit mammary gland phenotypes.

Methods

Mammary glands from nulliparous mice in our BK5.ATF3 colony, both non-transgenic and transgenic, were examined for anomalies by histopathology and immunohistochemistry. Nulliparous and biparous female mice were observed for possible mammary tumor development, and suspicious masses were analyzed by histopathology and immunohistochemistry. Human breast tumor samples, as well as normal breast tissue, were similarly analyzed for ATF3 expression.

Results

Transgenic BK5.ATF3 mice expressed nuclear ATF3 in the basal layer of the mammary ductal epithelium, and often developed squamous metaplastic lesions in one or more mammary glands by 25 weeks of age. No progression to malignancy was seen in nulliparous BK5.ATF3 or non-transgenic mice held for 16 months. However, biparous BK5.ATF3 mice developed mammary carcinomas with squamous metaplasia between 6 months and one year of age, reaching an incidence of 67%. Cytokeratin expression in the tumors was profoundly disturbed, including expression of CK5 and CK8 (characteristic of basal and luminal cells, respectively) throughout the epithelial component of the tumors, CK6 (potentially a stem cell marker), CK10 (a marker of interfollicular epidermal differentiation), and mIRSa2 and mIRSa3.1 (markers of the inner root sheath of hair follicles). Immunohistochemical studies indicated that a subset of human breast tumors exhibit high levels of nuclear ATF3 expression.

Conclusion

Overexpression of ATF3 in CK5-expressing cells of the murine mammary gland results in the development of squamous metaplastic lesions in nulliparous females, and in mammary tumors in biparous mice, suggesting that ATF3 acts as a mammary oncogene. A subset of human breast tumors expresses high levels of ATF3, suggesting that ATF3 may play an oncogenic role in human breast tumorigenesis, and therefore may be useful as either a biomarker or therapeutic target.

Comparison of Treatment Tolerance and Outcomes in Patients With Cervical Cancer Treated With Concurrent Chemoradiotherapy in a Prospective Randomized Trial or With Standard Treatment

PURPOSE

To compare the treatment and outcomes of cervical cancer patients treated with concurrent chemoradiotherapy (CT-RT) in a multi-institutional trial or as standard care.

PATIENTS AND METHODS

We reviewed the records of 302 patients treated with CT-RT for locoregionally confined, intact cervical cancer between 1990 and 2005. Of the 302 patients, 76 were treated using cisplatin and 5-fluorouracil (C/F) on Radiation Therapy Oncology Group protocol 90-01 (CT-RT(90-01)); 226 underwent CT-RT as standard care with either C/F [CT-RT(SC(C/F)); n = 115] or weekly cisplatin [CT-RT(SC(WC)); n = 111).

RESULTS

The CT-RT(90-01) patients more often had tumors >or=6 cm and were less often diabetic than were the CT-RT(SC) patients. The CT-RT(SC(WC)) patients were more likely than the CT-RT(SC(C/F)) patients to be >or=60 years old or to have Stage III-IV disease. During treatment, CT-RT(SC(C/F)) patients experienced more Grade 2-3 neutropenia and were, therefore, less likely to receive 200 mg/m(2) cisplatin than were either CT-RT(SC(WC)) or CT-RT(90-01) patients (52% vs. 77% vs. 85%, respectively; p <0.001). At 5 years, the disease-specific survival rates were greater for patients treated with C/F [CT-RT(SC(C/F)), 75%; CT-RT(90-01), 79%] than for those treated with CT-RT(SC(WC)) (58%; p = 0.02). On multivariate analysis, C/F chemotherapy, cisplatin dose >or=200 mg/m(2), Stage I-II disease, and negative pelvic lymph nodes were independent predictors of improved disease-specific survival.

CONCLUSIONS

Even within a large comprehensive cancer center, the high rates of chemotherapy completion achieved on a multi-institutional trial can be difficult to reproduce in standard practice. Although C/F toxicity was greater in the standard care patients, their outcomes were similar to those of patients treated with C/F on Radiation Therapy Oncology Group protocol 90-01.

The Ratio of Positive to Excised Nodes Identifies High-risk Subsets and Reduces Inter-Institutional Differences in Locoregional Recurrence Risk Estimates in Breast Cancer Patients With 1–3 Positive Nodes: An Analysis of Prospective Data From British Columbia and the M. D. Anderson Cancer Center

PURPOSE

To examine the power of the nodal ratio (NR) of positive/excised nodes in predicting postmastectomy locoregional recurrence (LRR) in patients with 1-3 positive nodes (N+) and in identifying cohorts at similar risk across independent data sets.

METHODS AND MATERIALS

Data from 82 patients with 1-3 N+ treated without postmastectomy radiotherapy (PMRT) in the British Columbia (BC) randomized trial were compared with data from 462 patients treated without PMRT in prospective chemotherapy trials at the M. D. Anderson Cancer Center (MDACC). Kaplan-Meier LRR curves were compared between centers using the absolute number of N+ and nodal ratios.

RESULTS

The median number of excised nodes was 10 in BC and 16 in MDACC (p < 0.001). Examining LRR by number of N+, the 10-year LRR rate for patients with 1-3 N+ was higher in BC compared with MDACC (21.5% vs. 12.6%; p = 0.02). However, when examining LRR using NR, no differences were found between institutions. In patients with NR < or = 0.20, the 10-year LRR rate was 17.7% BC vs. 10.9% MDACC (p = 0.27). In patients with NR > or = 0.20, the 10-year LRR rate was 28.7% BC vs. 22.7% MDACC (p = 0.32). On Cox regression analysis, NR was a stronger prognostic factor compared with number of N +.

CONCLUSIONS

In patients with 1-3 N+, evaluating nodal positivity using NR reduced inter-institutional differences in LRR estimates that may exist due to variations in numbers of nodes excised. Nodal ratio >0.20 was associated with LRR >20%, warranting PMRT consideration. Nodal ratio may be useful for extrapolating data from prospective trials to clinical practices in which axillary staging extent vary.

High-affinity triplex-forming oligonucleotide target sequences in mammalian genomes

Site-specific recognition of duplex DNA by triplex-forming oligonucleotides (TFOs) provides a promising approach to manipulate mammalian genomes. A prerequisite for successful gene targeting using this approach is that the targeted gene must contain specific, high-affinity TFO target sequences (TTS). To date, TTS have been identified and characterized in only approximately 37 human or rodent genes, limiting the application of triplex-directed gene targeting. We searched the complete human and mouse genomes using an algorithm designed to identify high-affinity TTS. The resulting data set contains 1.9 million potential TTS for each species. We found that 97.8% of known human and 95.2% of known mouse genes have at least one potential high-affinity TTS in the promoter and/or transcribed gene regions. Importantly, 86.5% of known human and 83% of the known mouse genes have at least one TTS that is unique to that gene. Thus, it is possible to target the majority of human and mouse genes with specific TFOs. We found substantially more potential TTS in the promoter sequences than in the transcribed gene sequences or intergenic sequences in both genomes. We selected 12 mouse genes and 2 human genes critical for cell signaling, proliferation, and/or carcinogenesis, identified potential TTS in each, and determined TFO binding affinities to these sites in vitro. We identified at least one high-affinity, specific TFO binding site within each of these genes. Using this information, many genes involved in mammalian cell proliferation and carcinogenesis can now be targeted.

Pimonidazole labelling and response to fractionated irradiation of five human squamous cell carcinoma (hSCC) lines in nude mice: The need for a multivariate approach in biomarker studies

OBJECTIVE

To investigate the influence on local control after fractionated radiotherapy of hypoxia measured in unirradiated tumours using the hypoxic marker Pimonidazole, using multivariate approaches.

MATERIAL AND METHODS

Five human squamous cell carcinoma lines (FaDu, UT-SCC-15, UT-SCC-14, XF354, and UT-SCC-5) were transplanted subcutaneously into the right hind-leg of NMRI nude mice. Histological material was collected from 60 unirradiated tumours after injection of Pimonidazole. The relative hypoxic area within the viable tumour area (Pimonidazole hypoxic fraction, pHF) was determined in seven serial 10 microm cross-sections per tumour by fluorescence microscopy and computerized image analysis. Local tumour control was evaluated in a total of 399 irradiated tumours at 120 days after 30 fractions given within 6 weeks with total doses between 30 and 115 Gy.

RESULTS

Tumour lines showed pronounced heterogeneity in both pHF and TCD50. Mean pHF values varied between 5% and 37%, TCD50 values between 47 and 130 Gy. A Cox Proportional Hazards model of time to recurrence with two covariates, dose and pHF, yielded significant contributions of both parameters on local control (p < 0.005) but violated the proportional hazards assumption, suggesting that other factors also influence tumour control. Introduction of histological grade as an example of a confounding factor into the model improved the fit significantly. Local control rates decreased with increasing pHF and this effect was more pronounced at higher doses.

CONCLUSIONS

This study confirms that tumour hypoxia measured using Pimonidazole in untreated tumours is a significant determinant of local control after fractionated irradiation. The data support the use of multivariate approaches for the evaluation of a single prognostic biomarker such as Pimonidazole, and more generally, suggest that they are required to establish accurate prognostic factors for tumour response.