A web-based search engine for triplex-forming oligonucleotide target sequences

Triplex technology offers a useful approach for site-specific modification of gene structure and function both in vitro and in vivo. Triplex-forming oligonucleotides (TFOs) bind to their target sites in duplex DNA, thereby forming triple-helical DNA structures via Hoogsteen hydrogen bonding. TFO binding has been demonstrated to site-specifically inhibit gene expression, enhance homologous recombination, induce mutation, inhibit protein binding, and direct DNA damage, thus providing a tool for gene-specific manipulation of DNA. We have developed a flexible web-based search engine to find and annotate TFO target sequences within the human and mouse genomes. Descriptive information about each site, including sequence context and gene region (intron, exon, or promoter), is provided. The engine assists the user in finding highly specific TFO target sequences by eliminating or flagging known repeat sequences and flagging overlapping genes. A convenient way to check for the uniqueness of a potential TFO binding site is provided via NCBI BLAST. The search engine may be accessed at spi.mdanderson.org/tfo.

Preclinical evaluation of molecular-targeted anticancer agents for radiotherapy

The combination of molecular-targeted agents with irradiation is a highly promising avenue for cancer research and patient care. Molecular-targeted agents are in themselves not curative in solid tumours, whereas radiotherapy is highly efficient in eradicating tumour stem cells. Recurrences after high-dose radiotherapy are caused by only one or few surviving tumour stem cells. Thus, even if a novel agent has the potential to kill only few tumour stem cells, or if it interferes in mechanisms of radioresistance of tumours, combination with radiotherapy may lead to an important improvement in local tumour control and survival. To evaluate the effects of novel agents combined with radiotherapy, it is therefore necessary to use experimental endpoints which reflect the killing of tumour stem cells, in particular tumour control assays. Such endpoints often do not correlate with volume-based parameters of tumour response such as tumour regression and growth delay. This calls for radiotherapy specific research strategies in the preclinical testing of novel anti-cancer drugs, which in many aspects are different from research approaches for medical oncology.

The impact of young age on locoregional recurrence after doxorubicin-based breast conservation therapy in patients 40 years old or younger: How young is “young”?

PURPOSE

The aim of this study was to investigate whether patients <35 years old have similar risk of locoregional recurrence after breast conservation therapy compared with patients 35 to 40 years old.

METHODS AND MATERIALS

We retrospectively reviewed records of 196 consecutive patients < or =40 years old who received breast conservation therapy (BCT) from 1987 to 2000 for breast cancer and compared outcomes between patients <35 years old with patients 35 to 40 years old. The majority of patients received neoadjuvant chemotherapy as part of their treatment. Multivariate analysis was performed to assess risk factors for locoregional recurrence.

RESULTS

After a median follow-up of 64 months, 22 locoregional recurrences (LRR) were observed. Twenty patients developed locoregional recurrence as their first site of relapse. Two patients had bone-only metastases before their locoregional recurrence. On multivariate analysis, age <35 years was associated with a statistically significant increased risk of locoregional recurrence. The 5-year rate of locoregional control was 87.9% in patients <35 years old compared with 91.7% in patients 35 to 40 years old (p = 0.042).

CONCLUSIONS

Our finding supports an increased risk of locoregional recurrence as a function of younger age after breast conservation therapy, even among young patients 40 years old and younger.

Increasing external beam dose for T1-T2 prostate cancer: effect on risk groups

PURPOSE

The aim of this study was to investigate effect of increasing dose on risk groups for clinical failure (CF: local failure or distant failure or hormone ablation or PSA>or=25 ng/ml) in patients with T1-T2 prostate cancer treated with external beam radiotherapy.

METHODS AND MATERIALS

Patients (n=4,537) were partitioned into nonoverlapping dose ranges, each narrow enough that dose was not a predictor of CF, and risk groups for CF were determined using recursive partitioning analysis (RPA). The same technique was applied to the highest of these dose ranges (70-76 Gy, 1,136 patients) to compare risk groups for CF in this dose range with the conventional risk-group classification.

RESULTS

Cutpoints defining low-risk groups in each dose range shifted to higher initial PSA levels and Gleason scores with increasing dose. Risk groups for CF in the dose range 70-76 Gy were not consistent with conventional risk groups.

CONCLUSIONS

The conventional classification of risk groups was derived in the early PSA era, when total doses<70 Gy were common, and it is inconsistent with risk groups for patients treated to doses>70 Gy. Risk-group classifications must be continuously re-examined whenever the trend is toward increasing total dose.

Cluster model analysis of late rectal bleeding after IMRT of prostate cancer: a case-control study

PURPOSE

Cluster models are newly developed normal-tissue complication probability models in which the spatial aspects of radiation-induced injury are taken into account by considering the size of spatially contiguous aggregates of damaged tissue units. The purpose of this study was to test the validity of a two-dimensional cluster model of late rectal toxicity based on maximum cluster size of damage to rectal surface.

METHODS AND MATERIALS

A paired case-control study was performed in which each of 9 patients experiencing Grade 2 or higher late rectal toxicity after intensity-modulated radiation therapy of localized prostate cancer was paired with a patient having a similar rectal dose-surface histogram but free of rectal toxicity. Numeric simulations were performed to determine the distribution of maximum cluster size on each rectal surface for each of many different choices of possible model parameters.

RESULTS

Model parameters were found for which patients with rectal toxicity were consistently more likely to have a significantly larger mean maximum cluster size than their matched controls. These parameter values correspond to a 50% probability of tissue-unit damage at doses near 30 Gy.

CONCLUSIONS

This study suggests that a cluster model based on maximum cluster size of damage to rectal surface successfully incorporates spatial information beyond that contained in the rectal dose-surface histogram and may therefore provide a useful new tool for predicting rectal normal-tissue complication probability after radiotherapy.

Decreased repopulation as well as increased reoxygenation contribute to the improvement in local control after targeting of the EGFR by C225 during fractionated irradiation

BACKGROUND AND PURPOSE

Inhibition of repopulation and enhanced reoxygenation has been suggested to contribute to improvement of local tumour control after fractionated irradiation combined with inhibitors of the epidermal growth factor receptor (EGFR). The present study addresses this hypothesis in FaDu human squamous cell carcinoma. For this tumour model marked repopulation and incomplete reoxygenation during fractionated irradiation has previously been demonstrated. Furthermore, the anti-EGFR monoclonal antibody C225 has been shown to significantly improve the results of fractionated irradiation in this tumour.

MATERIALS AND METHODS

FaDu tumours in nude mice were irradiated with 18 fractions in 18 days (18f/18d) or 18 fractions in 36 days (18f/36d). Three Gy fractions were given either under ambient or under clamp hypoxic conditions. C225 or carrier was applied four times during the course of treatment. Fractionated irradiations were followed by graded top-up doses to obtain complete dose-response curves for local tumour control. Tumour control dose 50% (TCD50) was determined at day 120 after end of treatment.

RESULTS

Significant repopulation and reoxygenation occurred during fractionated irradiation of FaDu tumours (P-values between 0.028 and <0.001). Application of C225 significantly decreased TCD50 for 18f/36d under ambient conditions (P=0.04). Bootstrap analysis revealed decreased repopulation and increased reoxygenation after application of C225 (P=0.06 for the combined effect). This was further corroborated by a significant effect of C225 on the 'repopulated' dose under ambient conditions which is influenced by both, reoxygenation and repopulation (P=0.012).

CONCLUSIONS

Our study provides evidence that both decreased repopulation as well as increased reoxygenation contribute to the improvement of local control after targeting of EGFR by C225 during fractionated irradiation of FaDu tumours.

Biochemical and clinical significance of the posttreatment prostate-specific antigen bounce for prostate cancer patients treated with external beam radiation therapy alone

BACKGROUND

The posttreatment prostate-specific antigen (PSA) bounce phenomenon has been recognized in at least 20% of all patients treated with radiation. The purpose of the current report was to determine if there was a difference in biochemical and clinical control between the bounce and nonbounce (NB) patients using pooled data on 4839 patients with T1-2 prostate cancer treated with external beam radiation therapy (RT) alone at 9 institutions between 1986 and 1995.

METHODS

The median follow-up was 6.3 years. A posttreatment PSA bounce was defined by a minimal rise of 0.4 ng/mL over a 6-month follow-up period, followed by a drop in PSA level of any magnitude. Endpoints included no biochemical evidence of disease (bNED) failure (BF) (ASTRO definition), distant failure (DF), cause-specific failure (CSF), and overall survival (OS). Patients were stratified by pretreatment PSA, Gleason score, T stage, age, dose, and risk group.

RESULTS

In all, 978 (20%) patients experienced at least 1 posttreatment PSA bounce. Within 3 subgroups (risk group, pretreatment PSA, and age), statistically significant differences of remaining bounce-free were observed on univariate analysis. Patients < 70 years had a 72% chance of remaining bounce-free at 5 years compared with 75% for older patients (P = .04). The NB patients had 72% bNED control at 10 years compared with 58% for the bounce patients. The effect of a bounce remained statistically significant on multivariate analysis (P < .0001). No statistically significant difference in DF, CSF, or OS was observed.

CONCLUSIONS

Patients treated with external beam radiation therapy alone who experience a posttreatment PSA bounce have increased risk of BF. However, this did not translate into a difference in clinical failure with the available follow-up in the current study.

PSA nadir predicts biochemical and distant failures after external beam radiotherapy for prostate cancer: a multi-institutional analysis

PURPOSE

To determine the significance of prostate-specific antigen (PSA) nadir (nPSA) and the time to nPSA (T(nPSA)) in predicting biochemical or clinical disease-free survival (PSA-DFS) and distant metastasis-free survival (DMFS) in patients treated with definitive external beam radiotherapy (RT) for clinical Stage T1b-T2 prostate cancer.

METHODS AND MATERIALS

Nine participating institutions submitted data on 4839 patients treated between 1986 and 1995 for Stage T1b-T2cN0-NxM0 prostate cancer. All patients were treated definitively with RT alone to doses > or =60 Gy, without neoadjuvant or planned adjuvant androgen suppression. A total of 4833 patients with a median follow-up of 6.3 years met the criteria for analysis. Two endpoints were considered: (1) PSA-DFS, defined as freedom from PSA failure (American Society for Therapeutic Radiology and Oncology definition), initiation of androgen suppression after completion of RT, or documented local or distant failure; and (2) DMFS, defined as freedom from clinically apparent distant failure. In patients with failure, nPSA was defined as the lowest PSA measurement before any failure. In patients without failure, nPSA was the lowest PSA measurement during the entire follow-up period. T(nPSA) was calculated from the completion of RT to the nPSA date.

RESULTS

A greater nPSA level and shorter T(nPSA) were associated with decreased PSA-DFS and DMFS in all patients and in all risk categories (low [Stage T1b, T1c, or T2a, Gleason score < or =6, and PSA level < or =10 ng/mL], intermediate [Stage T1b, T1c, or T2a, Gleason score < or =6, and PSA level >10 but < or =20 ng/mL, or Stage T2b or T2c, Gleason score < or =6, and PSA level < or =20 ng/mL, or Gleason score 7 and PSA level < or =20 ng/mL], and high [Gleason score 8-10 or PSA level >20 ng/mL]), regardless of RT dose. The 8-year PSA-DFS and DMFS rate for patients with nPSA <0.5 ng/mL was 75% and 97%; nPSA > or =0.5 but <1.0 ng/mL, 52% and 96%; nPSA > or =1.0 but <2.0 ng/mL, 40% and 91%; and nPSA > or =2.0 ng/mL, 17% and 73%, respectively. The 8-year PSA-DFS and DMFS rate for patients with T(nPSA) <6 months was 27% and 66%; T(nPSA) > or =6 but <12 months, 31% and 85%; T(nPSA) > or =12 but <24 months, 42% and 94%; and T(nPSA) > or =24 months, 75% and 99%, respectively. A shorter T(nPSA) was associated with decreased PSA-DFS and DMFS, regardless of the nPSA. Both nPSA and T(nPSA) were significant predictors of PSA-DFS and DMFS in multivariate models incorporating clinical stage, Gleason score, initial PSA level, and RT dose. The significance of nPSA and T(nPSA) was supported by landmark analysis, as well as by analysis of nPSA and T(nPSA) as time-dependent covariates. A dose > or =70 Gy was associated with a lower nPSA level and longer T(nPSA) in all risk categories, and a greater dose was significantly associated with greater PSA-DFS and DMFS in multivariate analysis. Regression analysis confirmed that higher clinical stage, Gleason score, and initial PSA were associated with a greater nPSA level.

CONCLUSION

The results of this large, multi-institutional analysis of 4833 patients have provided important evidence that nPSA and T(nPSA) after definitive external beam RT are not only predictive of a predominantly PSA endpoint (PSA-DFS), but are also predictive of distant metastasis in all clinical risk categories. Greater RT doses were associated with lower nPSA, longer T(nPSA), and improved PSA-DFS and DMFS.

Enhanced susceptibility of irradiated tumor vessels to vascular endothelial growth factor receptor tyrosine kinase inhibition

Previous experiments with PTK787/ZK222584, a specific inhibitor of vascular endothelial growth factor receptor (VEGFR) tyrosine kinases, using irradiated human FaDu squamous cell carcinoma in nude mice, suggested that radiation-damaged tumor vessels are more sensitive to VEGFR inhibition. To test this hypothesis, the tumor transplantation site (i.e., the right hind leg of nude mice) was irradiated 10 days before transplantation of FaDu to induce radiation damage in the host tissue. FaDu tumors vascularized by radiation-damaged blood vessels appeared later, grew at a slower rate, and showed more necrosis and a smaller vessel area per central tumor section than controls. PTK787/ZK222584 at a daily dose of 50 mg/kg body weight had no impact on growth of control tumors. In contrast, tumors vascularized by radiation-damaged vessels responded to PTK787/ZK222584 with longer latency and slower growth rate than controls, and a trend toward further increase in necrosis, indicating that irradiated tumor vessels are more susceptible to VEGFR inhibition than unirradiated vessels. Although not proving causality, expression analysis of VEGF and VEGFR2 shows that enhanced sensitivity of irradiated vessels to a specific inhibitor of VEGFR tyrosine kinases correlates with increased expression of the molecular target.

Does heterogeneity of pimonidazole labelling correspond to the heterogeneity of radiation-response of FaDu human squamous cell carcinoma?

BACKGROUND AND PURPOSE

Pimonidazole is a marker for hypoxic cells which are radioresistant and thereby important for the outcome of radiotherapy. The present study evaluates heterogeneity in pimonidazole binding within and between tumours and relates the results to the heterogeneity of radiation response in the same tumour cell line.

MATERIALS AND METHODS

FaDu, a poorly differentiated human squamous cell carcinoma line, was transplanted subcutaneously into the right hind-leg of NMRI nude mice. Tumours were irradiated with graded single doses either under ambient or clamped blood flow conditions and local tumour control was evaluated after 120 days. Complete dose-response curves for local tumour control were generated and the slope, a measure of heterogeneity of radiation response, was determined. In parallel, 12 unirradiated tumours were examined histologically. Seven serial 10 microm cross-sections per tumour were evaluated using fluorescence microscopy and computerised image analysis to determine the pimonidazole hypoxic fraction (pHF). Heterogeneity in pHF was quantified by its coefficient of variation (CV). Poisson-based model calculations considering the intertumoural heterogeneity of pHF were performed and the slopes of the predicted and the observed dose-response curves were compared.

RESULTS

The mean pHF was 11% [CV 50%] when one central section per tumour was evaluated. Measurements of multiple sections per tumour resulted in a mean pHF of 12% [CV 46%] (P=0.7). Intertumoural heterogeneity in pHF was more pronounced than heterogeneity in individual tumours by a factor of 2. Model calculations based on the variability in pHF resulted in similar slopes of the dose-response curve for local tumour control in comparison with the observed slope when the heterogeneity in an unknown and arbitrarily chosen additional radiobiologically relevant parameter, in this example clonogen density, was taken into account.

CONCLUSIONS

While the average pimonidazole hypoxic fraction in FaDu tumours corresponds well to the radiobiological hypoxic fraction, the variability of pHF in FaDu tumours was not sufficient to explain the heterogeneity of radiation response in the same tumour line. Information on at least one additional parameter is expected to substantially enhance the predictive power of histological markers of tumour hypoxia.

DEFINING RECURRENCE AFTER RADIATION FOR PROSTATE CANCER

PURPOSE

We reviewed prostate specific antigen (PSA) definitions of recurrence after external beam radiation for prostatic cancer and related them to the definitions used for other treatment modalities.

MATERIALS AND METHODS

The literature on defining recurrence after external beam radiation, brachytherapy and prostatectomy for prostate cancer was reviewed through a MEDLINE search to ensure completeness and the inclusion of all pertinent information.

RESULTS

Although the definition, which is the current standard for estimating recurrence after external beam radiation, has proved to be a reasonable measure, alternative options that are more sensitive and specific have now been defined. Similar statistical testing and comparison must also be done for other treatment modalities since the choice of failure definitions has not been evaluated nearly as thoroughly for these therapies. As much as possible, outcome reporting should be done according to the same method to ensure fairness when comparisons are made. However, inherent differences between treatment modalities and their effect on PSA production must also be considered.

CONCLUSIONS

With the latest available information from patients with long-term followup PSA definitions of tumor recurrence after external beam radiation for prostatic cancer must again be reviewed in a consensus conference format. The application of a universal PSA definition of tumor recurrence across multiple treatment modalities should also be explored.

Definitions of biochemical failure that best predict clinical failure in patients with prostate cancer treated with external beam radiation alone: a multi-institutional pooled analysis

PURPOSE

Pooled data on 4,839 patients with T1-2 prostate cancer treated with external beam radiation therapy (RT) alone at 9 institutions have previously provided long-term biochemical failure (BF) and clinical outcomes using the American Society for Therapeutic Radiology and Oncology (ASTRO) definition. In this report we determined the sensitivity and specificity of several BF definitions using distant failure (DF) alone or clinical failure (CF), defined as local failure (LF) and/or DF.

MATERIALS AND METHODS

The pooled cohort was treated between 1986 and 1995 with external beam RT (60 Gy or greater) without pre-RT androgen suppression or planned post-RT adjuvant androgen suppression. Median followup was 6.3 years. The sensitivity and specificity of 102 definitions of BF relative to DF and LF were assessed.

RESULTS

The BF definitions with higher sensitivity and specificity than the ASTRO definition for DF only and CF are reported. The sensitivity and specificity of the ASTRO definition to predict DF alone was 55% and 68%, respectively. Three definitions had higher sensitivity and specificity, namely prostate specific antigen (PSA) greater than current nadir (lowest PSA prior to current measurement) plus 3 ng/ml (sensitivity 76% and specificity 72%), dated at the call (failure date as the date when the criterion was met), PSA greater than absolute nadir plus 2 ng/ml (sensitivity 72% and specificity 70%), dated at the call, or 2 consecutive increases of at least 0.5 ng/ml, back dated (sensitivity 69% and specificity 73%). The sensitivity and specificity of the ASTRO definition to predict CF was 60% and 72%, respectively. Three definitions had higher sensitivity and specificity, namely PSA greater than current nadir plus 3 ng/ml (sensitivity 66% and specificity 77%), dated at the call, PSA greater than absolute nadir plus 2 ng/ml (sensitivity 64% and specificity 74%), dated at the call, or 2 consecutive increases of at least 0.5 ng/ml, back dated (sensitivity 67% and specificity 78%).

CONCLUSIONS

Using what is to our knowledge the largest data set of patients with prostate cancer treated with RT alone we correlated multiple definitions of BF with the strict clinical end points of DF alone and CF (DF or local failure). Defining BF as PSA greater than absolute nadir plus 2 ng/ml, dated at the call, PSA greater than current nadir plus 3 ng/ml, dated at the call, or 2 consecutive increases of at least 0.5 ng/ml, back dated, had higher sensitivity and specificity for DF alone or CF compared with the ASTRO definition. This information should contribute to the discussion regarding suggested modifications to the ASTRO definition of biochemical failure.

Recovery from sublethal damage during fractionated irradiation of human FaDu SCC

BACKGROUND AND PURPOSE

The present study addresses whether recovery of sublethal damage in tumours may change during fractionated irradiation in FaDu human squamous cell carcinoma and whether such an effect might contribute to the pronounced time factor of fractionated irradiation previously found in this tumour.

PATIENTS AND METHODS

FaDu tumours were transplanted s.c. into the right hind leg of NMRI nu/nu mice. Single doses or 2, 4, and 8 equal fractions in 3.5 days were applied in previously unirradiated tumours and after priming with 18 fractions of 3 Gy in 18 or 36 days. All irradiations were given under clamp hypoxic conditions. Experimental endpoints were tumour control dose 50% (TCD50) and alpha/ beta values without and after priming.

RESULTS

Without priming TCD50 increased with increasing number of fractions from 38.8 Gy (95% CI 35;45) after single dose irradiation to 54.0 Gy (42;57) after 8 fractions. No increase in TCD50 when given in 1, 2, 4, or 8 fractions in 3.5 days was found after priming with 18 3-Gy fractions in 18 and 36 days. After priming with 18 fractions in 18 days TCD50 remained constant at 25 Gy and after priming with 18 fractions in 36 days at 42 Gy. The alpha/beta ratio without priming was 68 Gy (42;127). After fractionated irradiation with 18 3-Gy fractions in 18 and 36 days the alpha/beta ratio increased to 317 Gy (38; infinity) and to infinite, respectively.

CONCLUSIONS

Our results indicate that clonogenic cells in FaDu tumours lose entirely their capacity to recover from sublethal radiation damage during fractionated irradiation. Therefore, an increased repair capacity as an explanation for the pronounced time factor of fractionated irradiation in this tumour can be ruled out.

Impact of adjuvant inhibition of vascular endothelial growth factor receptor tyrosine kinases on tumor growth delay and local tumor control after fractionated irradiation in human squamous cell carcinomas in nude mice

PURPOSE

Previous experiments have shown that adjuvant inhibition of the vascular endothelial growth factor receptor after fractionated irradiation prolonged tumor growth delay and may also improve local tumor control. To test the latter hypothesis, local tumor control experiments were performed.

METHODS AND MATERIALS

Human FaDu and UT-SCC-14 squamous cell carcinomas were studied in nude mice. The vascular endothelial growth factor receptor tyrosine kinase inhibitor PTK787/ZK222584 (50 mg/kg body weight b.i.d.) was administered for 75 days after irradiation with 30 fractions within 6 weeks. Tumor growth time and tumor control dose 50% (TCD(50)) were determined and compared to controls (carrier without PTK787/ZK222584).

RESULTS

Adjuvant administration of PTK787/ZK222584 significantly prolonged tumor growth time to reach 5 times the volume at start of drug treatment by an average of 11 days (95% confidence interval 0.06;22) in FaDu tumors and 29 days (0.6;58) in UT-SCC-14 tumors. In both tumor models, TCD(50) values were not statistically significantly different between the groups treated with PTK787/ZK222584 compared to controls.

CONCLUSIONS

Long-term inhibition of angiogenesis after radiotherapy significantly reduced the growth rate of local recurrences but did not improve local tumor control. This indicates that recurrences after irradiation depend on vascular endothelial growth factor-driven angiogenesis, but surviving tumor cells retain their clonogenic potential during adjuvant antiangiogenic treatment with PTK787/ZK222584.

Effect of reduced EGFR function on the radiosensitivity and proliferative capacity of mouse jejunal crypt clonogens

BACKGROUND AND PURPOSE

Previous data indicate that the EGFR pathway is involved in the response of tumor cell lines to irradiation. To determine if this receptor plays a role in the response of the intestinal mucosa, the effect of a spontaneous mutation in EGFR (B6C3-a-wa-2) on radiosensitivity and proliferative capacity was investigated using in vivo clonogenic assays and immunohistochemistry.

PATIENTS AND METHODS

EGFR mutant mice were compared with wild-type mice using the in vivo jejunal microcolony assay using single and split doses to measure the radiosensitivity and repopulation of clonogenic jejunal mucosal cells. In addition, paraffin-embedded tissue sections were assessed for proliferation (PCNA), DNA repair (Ku70 and gamma H2AX), and apoptosis (TUNEL) by immunofluorescent staining (wild-type vs. heterozygous only) at various times after 5 Gy single dose.

RESULTS

After the high doses used in the split-dose experiments, EGFR heterozygous and homozygous mutant mice were significantly more radiosensitive than their wild-type littermates. There was no clear difference in split-dose repair based on EGFR function. After 5 Gy single dose there were significantly more apoptotic cells within the crypts of heterozygous mice than of wild-type mice, beginning at 3h post irradiation. Decreased proliferation was observed only in the homozygous mutant mice. PCNA staining was lower in the heterozygous mice than in wild-type mice at 1 and 3 h post-5 Gy.

CONCLUSION

The results indicate that after high doses the radiosensitivity of EGFR mutant mice is significantly higher than that of wild-type, and that this could be the result of an increase in apoptosis rather than reduced DNA repair. Proliferative capacity was modestly reduced, but only in the homozygous mutants.

Comparison of rectal dose-wall histogram versus dose-volume histogram for modeling the incidence of late rectal bleeding after radiotherapy

PURPOSE

To compare the fits of normal-tissue complication probability (NTCP) models based on rectal dose-wall histograms (DWHs) vs. dose-volume histograms (DVHs) when the two are used to analyze a common set of late rectal toxicity data.

METHODS AND MATERIALS

Data were analyzed from 128 prostate cancer patients treated with 3-dimensional conformal radiotherapy (3D-CRT) at The University of Texas M.D. Anderson Cancer Center (UTMDACC). The DVH for total rectal volume, including contents, was obtained for each patient from the treatment-planning system. A DWH was also computed, using the outer rectal contour plus an autogenerated inner contour that corresponds to an assumed 3-mm rectal wall thickness. The endpoint for analysis was Grade 2 or higher late rectal bleeding within 2 years of treatment; all patients had at least 2 years of follow-up. Four different NTCP models were fitted to the response data by using either the DVH or the DWH to describe the dose distribution to rectum or rectal wall, respectively. The 4 models considered were the Lyman model, the mean dose model, the parallel-architecture model, and a model based on the volume of a organ receiving more than a specified dose (the "cutoff-dose" model).

RESULTS

For each of the models, the fit to the late rectal bleeding data was slightly improved when the analysis was based on the rectal DWH instead of on the DVH. In addition, the results of the cutoff dose and parallel architecture models were consistent with one another for the DWH data but not for the DVH data. For the DWH data, both models predict a 50% or higher incidence of Grade 2 or worse late rectal bleeding within 2 years if 80% or more of the rectal wall is exposed to doses greater than 32 Gy. A 50% or higher incidence of rectal bleeding is also predicted if the mean dose to rectal wall exceeds 53.2 Gy.

CONCLUSIONS

A consistent, although modest, improvement occurs in the fits of NTCP models to the UTMDACC 2-year late rectal bleeding data when the fit is based on the rectal dose-wall histogram instead of on the dose-volume histogram for entire rectum, including contents.

New anticancer agents: in vitro and in vivo evaluation

The rapid emergence of new anticancer agents is a tremendous challenge for basic, pre-clinical and clinical research to evaluate and eventually integrate these new agents into clinical routine. Standardized, well-established in vitro and in vivo methods are available for the experimental evaluation of new anticancer agents. A step-wise procedure from in vitro to in vivo experiments using non-functional, functional non-clonogenic and, if applicable, clonogenic assays allows reduction of the number of promising agents for further clinical testing.

Breast conservation after neoadjuvant chemotherapy

BACKGROUND

The appropriate selection criteria for breast-conserving therapy (BCT) after neoadjuvant chemotherapy are poorly defined. The purpose of the current report was to develop a prognostic index to help refine selection criteria and to serve as a general framework for clinical decision-making for patients treated by this multimodality approach.

METHODS

From a group of 340 patients treated with BCT after neoadjuvant chemotherapy, the authors previously determined 4 statistically significant predictors of ipsilateral breast tumor recurrence (IBTR) and locoregional recurrence (LRR): clinical N2 or N3 disease, residual pathologic tumor size > than 2 cm, a multifocal pattern of residual disease, and lymphovascular space invasion in the specimen. The M. D. Anderson Prognostic Index (MDAPI) was developed by assigning scores of 0 (favorable) or 1 (unfavorable) for each of these 4 variables and using the total to give an overall MDAPI score of 0-4.

RESULTS

The MDAPI stratified the 340 patients into 3 subsets with statistically different levels of risk for IBTR and LRR after neoadjuvant chemotherapy and BCT. Actuarial 5-year IBTR-free survival rates were 97%, 88%, and 82% for patients in the low (MDAPI overall score 0 or 1, n=276), intermediate (MDAPI score 2, n=43), and high (MDAPI score 3 or 4, n=12) risk groups, respectively (P<0.001). Corresponding actuarial 5-year LRR-free survival rates were 94%, 83%, and 58%, respectively (P<0.001).

CONCLUSIONS

Patients with an MDAPI score of 0 or 1, which made up 81% of the study population, had very low rates of IBTR and LRR. The MDAPI enabled the identification of a small group (4%) of patients who are at high risk for IBTR and LRR and who may benefit from alternative locoregional treatment strategies.

Clinically relevant pneumonitis after sequential paclitaxel-based chemotherapy and radiotherapy in breast cancer patients

BACKGROUND

Taxane-based chemotherapy has been associated with an increased risk of radiation pneumonitis in patients with breast cancer. To obtain additional information about this association, we investigated the association between paclitaxel chemotherapy and radiation pneumonitis in patients participating in a phase III randomized study.

METHODS

Five hundred and twenty-four breast cancer patients were prospectively and randomly assigned to receive either four cycles of paclitaxel followed by four cycles of 5-fluorouracil, doxorubicin, cyclophosphamide (FAC) or eight cycles of FAC. One hundred and eighty-nine of these patients (100 in the paclitaxel-FAC group and 89 in the FAC group) subsequently underwent radiation therapy in our institution and had medical records available to review for pulmonary symptoms. In addition, a radiologist who was unaware of the type of treatment scored chest x-ray changes after radiation treatment. Crude rates of radiation pneumonitis were compared with chi-square or Fisher's exact test, and actuarial rates were assessed with Kaplan-Meier and log-rank tests. All statistical tests were two-sided.

RESULTS

No difference in the rate of clinically relevant radiation pneumonitis was observed between the two groups (5.0% in the paclitaxel-FAC group versus 4.5% in the FAC group; difference = 0.5%, 95% CI = -6.6% to 5.5%; P = 1.00). Oral steroids for pneumonitis were taken by two patients in the paclitaxel-FAC group but by none in the FAC group, and no patient was hospitalized for or died of radiation pneumonitis. The paclitaxel-FAC group (39.3%) had a higher rate of radiographic changes after irradiation than the FAC group (23.7%; difference = 15.6%, 95% CI = -0.11% to 28.8%; P = .034).

CONCLUSION

Patients with breast cancer treated with sequential paclitaxel, FAC, and radiation therapy appeared to have a very low rate of clinically relevant radiation pneumonitis that was no different from that of patients treated with FAC alone.

Predicting radiosensitivity using DNA end-binding complex analysis

Previous reports have suggested that measuring radiosensitivity of normal and tumor cells would have significant clinical relevance for the practice of radiation oncology. We hypothesized that radiosensitivity might be predicted by analyzing DNA end-binding complexes (DNA-EBCs), which form at DNA double-strand breaks, the most important cytotoxic lesion caused by radiation. To test this hypothesis, the DNA-EBC pattern of 21 primary human fibroblast cultures and 15 tumor cell lines were studied. DNA-EBC patterns were determined using a modified electrophoretic mobility shift assay and were correlated with radiosensitivity, as measured by SF2. DNA-EBC analysis identified a rapidly migrating ATM-containing band (identified as "band-A") of which the density correlated with SF2 (0.02 </= SF2 </= 0.41) in primary fibroblasts (r(2) = 0.77). The DNA-EBC pattern of peripheral blood lymphocytes was identical to that of fibroblasts. In addition, band-A density correlated with SF2 (0.35 </= SF2 </= 0.80) in 15 human tumor cell lines (r(2) = 0.91). Densitometry of other bands, or total DNA-EBC binding, correlated more poorly with SF2 (r(2) < 0.45). These data indicate that DNA-EBC analysis may be a practical, clinically relevant predictor of tumor and primary cell radiosensitivity.

Cluster models of dose–volume effects

PURPOSE

Describe cluster models, normal-tissue complication probability models in which both the number and the spatial location of radiation-sterilized functional subunits play a role in defining complication probability.

METHODS AND MATERIALS

Computer simulation was used to determine the maximum size cluster of sterilized subunits associated with a given dose distribution. Complications were associated with large clusters.

RESULTS

Cluster models showed a volume effect, as increasing effect for constant dose when the volume increased or constant effect when the dose was reduced with increasing volume. Cluster models gave similar results to existing models when tissues were irradiated uniformly. With inhomogeneous dose distributions, on the other hand, different spatial distributions of "hot spots" may lead to different predictions of complication probability by cluster models. The result was that a higher complication probability resulted when hot spots were contiguous (clustered) than when they were dispersed, even if both situations are characterized by the same dose-volume histogram. A potential advantage of cluster models is to provide an easy, internally consistent way to predict complications arising from the inhomogeneous dose distributions that sometimes arise with intensity-modulated radiotherapy.

CONCLUSION

Cluster models offer a new way to quantify complication probability in treatment situations in which a wide variety of hot-spot distributions occur.

Factors predictive of having four or more positive axillary lymph nodes in patients with positive sentinel lymph nodes: implications for selection of radiation fields

PURPOSE

The optimal design of radiation fields for patients with positive sentinel lymph nodes (SLNs) who do not undergo axillary dissection is unknown. We have previously shown that modified breast tangent fields can include most axillary Level I-II lymph nodes. We have also reported that irradiation of the axillary apex/supraclavicular fossa is indicated for patients with four or more positive axillary lymph nodes. To determine the optimal arrangement for patients with positive SLNs, we studied what factors predicted for having four or more positive lymph nodes.

METHODS AND MATERIALS

We reviewed the records of 339 consecutive patients with one to three positive SLNs who underwent complete axillary dissection at our institution between 1995 and 2002. We separately analyzed the outcome for those initially treated with surgery (n = 265) and those receiving neoadjuvant chemotherapy (n = 74). A logistic regression model was used to identify independent factors predictive for four or more positive lymph nodes.

RESULTS

A total of 28 of 265 patients in the initial surgery group and 20 of 74 patients in the neoadjuvant group had four or more positive lymph nodes. In the initial surgery group, the independent factors associated with four or more positive lymph nodes were no drainage seen on lymphoscintigraphy (rate, 38%, odds ratio [OR] = 5.4, p = 0.03), more than one positive SLN (rate, 24-42%, OR = 2.9, p = 0.02), and lymphovascular space invasion (LVSI; rate, 25%, OR = 4.8, p = 0.01). Of the 106 patients without any of these factors, only 2 had four or more positive lymph nodes. For the patients treated with neoadjuvant chemotherapy, the independent factors were clinical Stage III (rate, 48%, OR = 3.1, p = 0.03), more than one positive SLN (rate, 37-67%, OR = 4.8, p = 0.03), and LVSI (rate, 62%, OR = 8.1, p = 0.02). Of the 28 patients without any of these factors, only 1 had four or more positive lymph nodes.

CONCLUSION

It is reasonable to treat with modified tangents fields that include most axillary Level I-II nodes for patients with one positive SLN who do not undergo axillary dissection if drainage is seen on lymphoscintigraphy and no LVSI is present. This approach is also reasonable for patients treated with neoadjuvant chemotherapy who have Stage II disease, no LVSI, and only one positive SLN. The remaining patients have a greater risk of having four or more positive lymph nodes, and, therefore, the high axilla/supraclavicular fossa should also be included in the radiation fields.

Breast conservation after neoadjuvant chemotherapy: the MD Anderson cancer center experience

PURPOSE

To determine patterns of local-regional recurrence (LRR) and ipsilateral breast tumor recurrence (IBTR) among patients treated with breast conservation therapy after neoadjuvant chemotherapy.

PATIENTS AND METHODS

Between 1987 and 2000, 340 cases of breast cancer were treated with neoadjuvant chemotherapy followed by conservative surgery and radiation therapy. Clinical stage at diagnosis (according to the 2003 American Joint Committee on Cancer system) was I in 4%, II in 58%, and III in 38% of patients. Only 4% had positive surgical margins.

RESULTS

At a median follow-up period of 60 months (range, 10 to 180 months), 29 patients had developed LRR, 16 of which were IBTRs. Five-year actuarial rates of IBTR-free and LRR-free survival were 95% and 91%, respectively. Variables that positively correlated with IBTR and LRR were clinical N2 or N3 disease, pathologic residual tumor larger than 2 cm, a multifocal pattern of residual disease, and lymphovascular space invasion in the specimen. The presence of any one of these factors was associated with 5-year actuarial IBTR-free and LRR-free survival rates of 87% to 91% and 77% to 84%, respectively. Initial T category (T1-2 v T3-4) correlated with LRR but did not correlate with IBTR (5-year IBTR-free rates of 96% v 92%, respectively, P =.19).

CONCLUSION

Breast conservation therapy after neoadjuvant chemotherapy results in acceptably low rates of LRR and IBTR in appropriately selected patients, even those with T3 or T4 disease. Advanced nodal involvement at diagnosis, residual tumor larger than 2 cm, multifocal residual disease, and lymphovascular space invasion predict higher rates of LRR and IBTR.

Dose–volume response analyses of late rectal bleeding after radiotherapy for prostate cancer

PURPOSE

To compare the fits of various normal tissue complication probability (NTCP) models to a common set of late rectal toxicity data, with the aim of identifying the best model for predicting late rectal injury after irradiation.

METHODS AND MATERIALS

Late toxicity data from 128 prostate cancer patients treated on protocol with three-dimensional conformal radiotherapy at The University of Texas M.D. Anderson Cancer Center (UTMDACC) were analyzed. The dose-volume histogram for total rectal volume, including contents, was obtained for each patient, and the presence or absence of Grade 2 or worse rectal bleeding within 2 years of treatment was scored. Five different NTCP models were fitted to the data using maximum likelihood analysis: the Lyman model, the mean dose model, a parallel architecture model, and models based on either a cutoff dose or a cutoff volume.

RESULTS

All five of the NTCP models considered provided very similar fits to the UTMDACC rectal bleeding data. In particular, none of the more highly parameterized models (the four-parameter parallel model, three-parameter Lyman model, or three-parameter cutoff dose and volume models) provided a better fit than the simplest of the models, the two-parameter NTCP model describing rectal bleeding as a probit function of mean dose to rectum.

CONCLUSION

No dose-volume response model has yet been identified that provides a better description of the UTMDACC rectal toxicity data than the mean dose model. Because this model has relatively low predictive accuracy, the need to identify a better model remains.