A planning comparison of 7 irradiation options allowed in RTOG 1005 for early-stage breast cancer

Sequential or simultaneous-integrated boost in early-stage breast cancer patients: trade-offs between skin toxicity and risk of compromised coverage

PURPOSE

To determine the dosimetric effects of set-up errors on boost coverage, and compares skin toxicity of sequential and simultaneous boost techniques for left-sided breast cancer.

MATERIALS AND METHODS

This retrospective study included 23 early-stage breast cancer cases. Single isocenter HFWBI-SIB(s-SIB), single isocenter HFWBI-SB(s-SB) and dual isocenter HFWBI-SB(d-SB) were planing. Rotations of 0.5°, 1°, and 2° coupled with translationals of 0.5 mm, 1.0 mm, and 2.0 mm were applied along three orthogonal axes. The dose to 95% of the PTV (D95) and the volume covered by 95% of the prescribed dose (V95) were evaluated using GEE univariate analysis to determine how PTV coverage was related to 1/CIRTOG, PTVboost volume, PTVboost separation to isocenter. The relationship between the high-dose regions within the PTVbreast and Ratio_V was evaluated using univariate analysis.

RESULTS

The s-SIB had optimal target coverage and lower high-dose volume, but it increased the risk of compromised coverage to tumor bed. For the s-SB technique, V95 exceeded 95% under all setup errors. At 2.0° coupled with 2.0 mm, s-SIB and d-SB exhibited V95 values below 95% in 34.8% and 8.7% of cases, respectively. At other setup errors, both s-SIB and d-SB demonstrated V95 values greater than 95%. Notably, high-dose regions such as V105%, V107%, and V110% within the PTVbreast across the three techniques displayed a significant correlation with Ratio_V.

CONCLUSION

Simultaneous-integrated boost for early-stage breast cancer can reduce skin toxicity compared to sequential techniques but with the risk of compromising tumor bed coverage.

Hypofractionated radiotherapy with simultaneous tumor bed boost (Hi-RISE) in breast cancer patients receiving upfront breast-conserving surgery: study protocol for a phase III randomized controlled trial

BACKGROUND

The effectiveness and safety of moderately hypofractionated radiotherapy (HFRT) in patients undergoing breast-conserving surgery (BCS) has been demonstrated in several pivotal randomized trials. However, the feasibility of applying simultaneous integrated boost (SIB) to the tumor bed and regional node irradiation (RNI) using modern radiotherapy techniques with HFRT needs further evaluation.

METHODS

This prospective, multi-center, randomized controlled, non-inferiority phase III trial aims to determine the non-inferiority of HFRT combined with SIB (HFRTsib) compared with conventional fractionated radiotherapy with sequential boost (CFRTseq) in terms of five-year locoregional control rate in breast cancer patients undergoing upfront BCS. A total of 2904 participants will be recruited and randomized in a 1:1 ratio into the HFRTsib and CFRTseq groups. All patients will receive whole breast irradiation, and those with positive axillary nodes will receive additional RNI, including internal mammary irradiation. The prescribed dose for the HFRTsib group will be 40 Gy in 15 fractions, combined with a SIB of 48 Gy in 15 fractions to the tumor bed. The CFRTseq group will receive 50 Gy in 25 fractions, with a sequential boost of 10 Gy in 5 fractions to the tumor bed.

DISCUSSION

This trial intends to assess the effectiveness and safety of SIB combined with HFRT in early breast cancer patients following BCS. The primary endpoint is locoregional control, and the results of this trial are expected to offer crucial evidence for utilizing HFRT in breast cancer patients after BCS.

TRIAL REGISTRATION

This trial was registered at ClincalTrials.gov (NCT04025164) on July 18, 2019.

Special Techniques of Adjuvant Breast Carcinoma Radiotherapy

Modern radiotherapy techniques are designed to permit reduced irradiation of healthy tissue, resulting in a diminished risk of adverse effects and shortened recovery times. Several randomized studies have demonstrated the benefits of increased dosage to the tumor bed area in combination with whole breast irradiation (WBI). Conventional WBI treatment following breast-conserving procedures, which required 5-7 weeks of daily treatments, has been reduced to 3-4 weeks when using hyperfractionated regimens. The dosage administration improves local control, albeit with poorer cosmesis. The method of accelerated partial breast irradiation (APBI) shortens the treatment period whilst reducing the irradiated volume. APBI can be delivered using intraoperative radiation, brachytherapy, or external beam radiotherapy. Currently available data support the use of external beam partial breast irradiation in selected patients. Modern radiotherapy techniques make it possible to achieve favorable cosmesis in most patients undergoing immediate breast reconstruction surgery, and studies confirm that current methods of external beam radiation allow an acceptable coverage of target volumes both in the reconstructed breast and in the regional lymphatic nodes.

Treatment Planning Study for Microbeam Radiotherapy Using Clinical Patient Data

Microbeam radiotherapy (MRT) is a novel, still preclinical dose delivery technique. MRT has shown reduced normal tissue effects at equal tumor control rates compared to conventional radiotherapy. Treatment planning studies are required to permit clinical application. The aim of this study was to establish a dose comparison between MRT and conventional radiotherapy and to identify suitable clinical scenarios for future applications of MRT. We simulated MRT treatment scenarios for clinical patient data using an inhouse developed planning algorithm based on a hybrid Monte Carlo dose calculation and implemented the concept of equivalent uniform dose (EUD) for MRT dose evaluation. The investigated clinical scenarios comprised fractionated radiotherapy of a glioblastoma resection cavity, a lung stereotactic body radiotherapy (SBRT), palliative bone metastasis irradiation, brain metastasis radiosurgery and hypofractionated breast cancer radiotherapy. Clinically acceptable treatment plans were achieved for most analyzed parameters. Lung SBRT seemed the most challenging treatment scenario. Major limitations comprised treatment plan optimization and dose calculation considering the tissue microstructure. This study presents an important step of the development towards clinical MRT. For clinical treatment scenarios using a sophisticated dose comparison concept based on EUD and EQD2, we demonstrated the capability of MRT to achieve clinically acceptable dose distributions.

The dosimetric impact of axillary nodes contouring variability in breast cancer radiotherapy: an AIRO multi-institutional study

AIM

To quantify the dosimetric impact of contouring variability of axillary lymph nodes (L2, L3, L4) in breast cancer (BC) locoregional radiotherapy (RT).

MATERIALS AND METHODS

18 RT centres were asked to plan a locoregional treatment on their own planning target volume (single centre, SC-PTV) which was created by applying their institutional margins to the clinical target volume of the axillary nodes of three BC patients (P1, P2, P3) previously delineated (SC-CTV). The gold standard CTVs (GS-CTVs) of P1, P2 and P3 were developed by BC experts' consensus and validated with STAPLE algorithm. For each participating centre, the GS-PTV of each patient was created by applying the same margins as those used for the SC-CTV to SC-PTV expansion and replaced the SC-PTV in the treatment plan. Datasets were imported into MIM v6.1.7 [MIM Software Inc.], where dose-volume histograms (DVHs) were extracted and differences were analysed.

RESULTS

17/18 centres used intensity-modulated RT (IMRT). The CTV to PTV margins ranged from 0 to 10 mm (median 5 mm). No correlation was observed between GS-CTV coverage by 95% isodose and GS-PTV margins width. Doses delivered to 98% (D98) and 95% (D95) of GS-CTVs were significantly lower than those delivered to the SC-CTVs. No significant difference between SC-CTV and GS-CTV was observed in maximum dose (D2), always under 110%. Mean dose ≥ 99% of the SC-CTVs and GS-CTVs was satisfied in 84% and 50%, respectively. In less than one half of plans, GS-CTV V95% was above 90%. Breaking down the GS-CTV into the three nodal levels (L2, L3 and L4), L4 had the lowest probability to be covered by the 95% isodose.

CONCLUSIONS

Overall, GS-CTV resulted worse coverage, especially for L4. IMRT was largely used and CTV-to-PTV margins did not compensate for contouring issues. The results highlighted the need for delineation training and standardization.

Split-VMAT technique to control the deep inspiration breath hold time for breast cancer radiotherapy

BACKGROUND

To improve split-VMAT technique by optimizing treatment delivery time for deep-inspiration breath hold (DIBH) radiotherapy in left-sided breast cancer patients, when automatic beam-interruption devices are not available.

METHODS

Ten consecutive patients were treated with an eight partial arcs (8paVMAT) plan, standard of care in our center. A four partial arcs (4paVMAT) plan was also created and actual LINAC outputs were measured, to evaluate whether there was a dosimetric difference between both techniques and potential impact on the delivered dose. Subsequently, ten other patients were consecutively treated with a 4paVMAT plan to compare the actual treatment delivery time between both techniques. The prescribed dose was 40.05 Gy/15 fractions on the PTV breast (breast or thoracic wall), lymph nodes (LN) and intramammary lymph node chain (IMN). Treatment delivery time, PTVs coverage, conformity index (CI), organs at risk (OAR) dose, monitor units (MU), and gamma index were compared.

RESULTS

Both split-VMAT techniques resulted in similar dose coverage for the PTV Breast and LN, and similar CI. For PTV IMN we observed a 5% increased coverage for the volume receiving ≥ 36 Gy with 4paVMAT, with an identical volume receiving ≥ 32 Gy. There was no difference for the OAR sparing, with the exception of the contralateral organs: there was a 0.6 Gy decrease for contralateral breast mean (p ≤ 0.01) and 1% decrease for the volume of right lung receiving ≥ 5 Gy (p = 0.024). Overall, these results indicate a modest clinical benefit of using 4paVMAT in comparison to 8paVMAT. An increase in the number of MU per arc was observed for the 4paVMAT technique, as expected, while the total number of MU remained comparable for both techniques. All the plans were measured with the Delta4 phantom and passed the gamma index criteria with no significant differences. Finally, the main difference was seen for the treatment delivery time: there was a significant decrease from 8.9 to 5.4 min for the 4paVMAT plans (p < .05).

CONCLUSIONS

This study is mainly of interest for centers who are implementing the DIBH technique without automatic beam-holding devices and who therefore may require to manually switch the beam on and off during breast DIBH treatment. Split-VMAT technique with 4 partial arcs significantly reduces the treatment delivery time compared to 8 partial arcs, without compromising the target coverage and the OAR sparing. The technique decreases the number of breath holds per fraction, resulting in a shorter treatment session.

Excluding Lung Tissue from the PTV during Internal Mammary Irradiation. A Safe Technique for OAR-Sparing?

Simple Summary

The planning treatment volume (PTV) during internal mammary irradiation (IMNI) regularly overlaps with lung tissue and is often in close proximity to the heart. Thus, exclusion of lung tissue from the PTV is a potential technique to spare the organs at risk (OARs) during adjuvant breast cancer irradiation. Using an innovative dose recalculation and accumulation algorithm, we evaluated the safety of exclusion of lung tissue from the PTV. According to our data, exclusion of lung tissue from the PTV to spare the OARs leads to significant dose reduction in the target volume and can, therefore, not be recommended.

Abstract

The current study aims to determine whether exclusion of lung tissue from planning treatment volume (PTV) is a valid organ at risk (OAR)-sparing technique during internal mammary irradiation (IMNI). Twenty patients with left-sided breast cancer undergoing adjuvant radiotherapy including IMNI after mastectomy or lumpectomy with daily ConeBeam CT (CBCT; median n = 28) were enrolled in the current study. The daily dose distribution of the patients was estimated by recalculating treatment plans on CBCT-scans based on a standard PTV (PTV margin: 5mm-STD) and a modified PTV, which excluded overlapping lung tissue (ExLung). Using 3D-deformable dose accumulation, the dose coverage in the target volume was estimated in dependence of the PTV-margins. The estimated delivered dose in the IMN-CTV was significantly lower for the ExLung PTV compared to the STD PTV: ExLung: V95%: 76.6 ± 22.9%; V90%: 89.6 ± 13.2%, STD: V95%: 95.6 ± 7.4%; V90%: 99.1 ± 2.7%. Daily CBCT imaging cannot sufficiently compensate the anatomic changes and intrafraction movement throughout the treatment. Therefore, to ensure adequate delivery of the prescribed dose to the IMN-CTV, exclusion of lung tissue from the PTV to spare the OARs is not recommended.

Using Robust Optimization for Skin Flashing in Intensity Modulated Radiation Therapy for Breast Cancer Treatment: A Feasibility Study

PURPOSE

To study the feasibility and the effectiveness of a novel implementation of robust optimization on 2 sets of computed tomography (CT) data simultaneously for skin flashing in intensity modulated radiation therapy for breast cancer.

METHOD AND MATERIALS

Five patients who received treatment to the breast and regional lymphatics were selected for this study. For each patient, 3 plans were generated using 3 different skin-flashing methods, including (1) a manual flash plan with optimization on the nominal planning target volume (PTV) not extending beyond the skin that required manually postplanning the opening of the multi-leaf collimator and jaw to obtain flash; (2) an expanded PTV plan with optimization on an expanded PTV that included the target in the air beyond the skin; and (3) a robust-optimized (RO) plan using robust optimization that simultaneously optimizes on the nominal CT data set and a simulated geometry error CT data set. The feasibility and the effectiveness of the robust optimization approach was investigated by comparing it with the 2 other methods. The robustness of the plan against target position variations was studied by simulating 0-, 5-, 10-, and 15-mm geometry errors.

RESULTS

The RO plans were the only ones able to meet acceptable criteria for all patients in both the nominal and simulated geometry error scenarios. The expanded PTV plans developed major deviation on the maximum dose to the PTV for 1 patient. For the manual flash plans, every patient developed major deviation either on 95% of the dose to the PTV or the maximum dose to the PTV in the simulated geometry error scenarios. The RO plan demonstrated the best robustness against the target position variation among the 3 methods of skin flashing. The doses to the lung and heart were comparable for all 3 planning techniques.

CONCLUSION

Using robust optimization for skin flash in breast intensity modulated radiation therapy planning is feasible. Further investigation is warranted to confirm the clinical effectiveness of this novel approach.

Adjuvant whole breast radiotherapy with simultaneous integrated boost to tumor bed with intensity modulated radiotherapy technique in elderly breast cancer patients

Background

Adjuvant whole breast radiotherapy is the standard of care for breast cancer patients after partial mastectomy. Intensity-modulated radiation therapy (IMRT) has been reported to reduce acute toxicities compared to conventional radiotherapy. IMRT with simultaneous integrated boost (SIB) technique can deliver higher doses to tumor bed and irradiate whole breast with a lower dose level to shorten overall treatment duration. This study presents the long-term results of adjuvant IMRT with SIB in elderly breast cancer patients who received partial mastectomy.

Methods

From January 2007 to January 2018, 93 elder breast cancer patients (≥65-year-old) who received IMRT with SIB technique after partial mastectomy were reviewed retrospectively. The axillary areas were managed with either sentinel lymph node biopsies or axillary lymph node dissection. The dose to whole breast was 50.4 Gy in 28 fractions in all patients and the dose to tumor bed was 61.6 to 66.4 Gy in 28 fractions. The primary end point is locoregional control. Secondary end points include: overall survival, breast cancer-specific survival, distant-metastases-free survival, disease-free survival, and acute and chronic toxicities.

Results

The median follow-up was 56.1 months. One patient had ipsilateral breast tumor recurrence, 3 patients had regional lymph node recurrence, and 9 patients had distant metastases. Death occurred in 5 patients, including 3 patients died of breast cancer progression. Five-year overall survival is 96.3% and 5-year locoregional recurrence-free survival is 96.4%. The 5-year breast cancer specific survival and 5-year distant metastases-free survival is 97.5% and 87.2%, respectively. Seven patients developed second primary cancer after RT. Eighty-one point seven percent patients had acute grade 1 dermatitis while 18.3% suffered from grade 2 dermatitis. The incidence of grade 1 pneumonitis and grade 1 stomatitis was 4.3% and 8.6%, respectively.

Conclusions

Adjuvant IMRT with SIB technique is a safe and effective treatment strategy for elderly breast cancer patients after partial mastectomy.

Variability in lymph node irradiation in patients with breast cancer-results from a multi-center survey in German-speaking countries

PURPOSE

Lymph node irradiation in breast cancer has gained complexity due to recently published studies and technical innovations which then led to changes in international guidelines. We sought to determine real-time variability in lymph node irradiation in clinical practice in German-speaking countries.

METHODS

The Department of Radiation Oncology, Technical University of Munich (TUM), developed an online-based questionnaire focusing on the indication, target definition, and treatment technique of lymph node irradiation in patients with breast cancer. The invitation to participate in the survey was sent to members of the German Society of Radiation Oncology (DEGRO) by e‑mail. The results of the survey were exported from the online platform into SPSS for a detailed analysis.

RESULTS

In total, 100 physicians completed the questionnaire between 05/2019 and 06/2019. Despite the existence of several treatment and contouring guidelines, we observed large variability of lymph node irradiation: The guideline recommendation for internal mammary irradiation is not consistently implemented in clinical practice and irradiation of the axilla after positive SLNB (sentinel lymph node biopsy) or ALND (axillary lymph node dissection) is handled very differently. Furthermore, in most clinics, the ESTRO (European Society for Therapeutic Radiology and Oncology) contouring consensus is not used, and PTV (planning target volume) definitions and margins vary considerably.

CONCLUSION

Further clinical studies should be performed with a particular focus on radiotherapy for lymphatic drainage to support and amend the existing guidelines. These studies should establish a more standardized treatment of the lymph node regions in clinical practice. Quality assurance should enforce broad implementation of consensus recommendations.

Integration of biological factors in the treatment plan evaluation in breast cancer radiotherapy

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This study suggests a PQM methodology for breast cancer radiotherapy evaluation.

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The risk/benefit balance estimation includes tumor biology and smoking status.

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Smoking status influenced risk/benefit balance for different treatment techniques.

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Survival benefit dominated for all patients with high-risk breast cancer.

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Survival benefit for smokers with low- or intermediate- risk cancer was not seen.

Background/purpose

Tumor biology and patient smoking status have clear effects on the benefit of breast radiotherapy. This study developed treatment evaluation strategies that integrated dosimetry, tumor aggressiveness and smoking status for patients undergoing hypo-fractionated whole breast irradiation with simultaneous integrated boost.

Materials/methods

The evaluation method Plan Quality Metrics (PQM) was adapted for breast cancer. Radiotherapy (RT) benefit was assessed for three levels of tumor aggressiveness; RT risk was estimated using mean dose to organs at risk and published Excess Relative Risk per Gy data for lung cancer and cardiac mortality for smokers and non-smokers. Risk for contralateral breast cancer was also evaluated. PQM and benefit/risk was applied to four patient groups (n = 10 each). Plans using 3D conformal radiotherapy (3DCRT), 3DCRT plus intensity-modulated radiation therapy (IMRT), 3DCRT plus volumetric modulated arc therapy (VMAT) and VMAT were evaluated for each patient.

Results

3DCRT-IMRT hybrid planning resulted in higher PQM score (median 87.0 vs. 3DCRT 82.4, p < 0.01), better dose conformity, lower doses to the heart, lungs and contralateral breast. Survival benefit was most predominant for patients with high-risk breast cancer (>7% and >4.5% gain for non-smokers and smokers). For smokers with intermediate- or low-risk breast cancer, RT induced mortality risk dominated for all techniques. When considering the risk of local recurrence, RT benefitted also smokers (>5% and >2% for intermediate- and low-risk cancer).

Conclusions

PQM methodology was suggested for breast cancer radiotherapy evaluation. Further validation is needed. RT was beneficial for all patients with high risk of recurrence. A survival benefit for smokers with low or intermediate risk of recurrence could not be confirmed.

Dosimetric evaluation and systematic review of radiation therapy techniques for early stage node-negative breast cancer treatment

Radiation therapy (RT) is essential in treating women with early stage breast cancer. Early stage node-negative breast cancer (ESNNBC) offers a good prognosis; hence, late effects of breast RT becomes increasingly important. Recent literature suggests a potential for an increase in cardiac and pulmonary events after RT. However, these studies have not taken into account the impact of newer and current RT techniques that are now available. Hence, this review aimed to evaluate the clinical evidence for each technique and determine the optimal radiation technique for ESNNBC treatment. Currently, six RT techniques are consistently used and studied: 1) prone positioning, 2) proton beam RT, 3) intensity-modulated RT, 4) breath-hold, 5) partial breast irradiation, and 6) intraoperative RT. These techniques show dosimetric promise. However, limited data on late cardiac and pulmonary events exist due to challenges in long-term follow-up. Moving forward, future studies are needed to validate the efficacy and clinical outcomes of these current techniques.

Recent Developments in Radiation Oncology: An Overview of Individualised Treatment Strategies in Breast Cancer

Radiation therapy (RT) for breast cancer has dramatically changed over the past years, leading to individualized risk-adapted treatment strategies. Historically, the choice of RT regimen was limited to conventional fractionation protocols using standard tangential fields. Nowadays, technological and technical improvements in modern RT have added a variety of other RT modalities, different fractionation schedules, and individualised treatment volumes to the portfolio of breast RT. This review aims to give a short overview on the main topics which have recently found their way into clinical practice: hypofractionated treatment protocols, accelerated partial breast irradiation (APBI) for low-risk patients, deep inspiration breath hold (DIBH) for maximal heart protection, extent of regional nodal irradiation for high-risk patients, and the implementation of new radiation techniques such as intensity modulated RT (IMRT) and volumetric modulated RT (VMAT).

Optimal radiation dose for patients with one to three lymph node positive breast cancer following breast-conserving surgery and anthracycline plus taxane-based chemotherapy: A retrospective multicenter analysis (KROG 1418)

Background and Purpose

This study was performed to determine optimal radiation dose in pN1 breast cancer patients who received breast conserving surgery (BCS) and anthracycline plus taxane (AT)-based chemotherapy.

Materials and Methods

Retrospective chart reviews were performed in 1,147 patients who were treated between January 2006 and December 2010. The impact of radiation dose on treatment outcomes was evaluated.

Results

Median follow-up time was 66 months. The 5-year rate of disease-free survival (DFS) was 93.2%. Larger tumor size (> 20 mm), positive lymphovascular invasion, high histologic grade, and high ratio of positive nodes (> 0.1) were significantly associated with inferior DFS. By using the 4 factors related to DFS, patients were categorized into high-risk (with ≥ 3 factors) and low-risk (with < 3 factors) groups. In the high-risk group, higher radiation dose (> 60.3 Gy_EQD2) was significantly associated with better DFS than the lower dose (≤ 60.3 Gy_EQD2). However, the radiation dose did not impact DFS in the low-risk group.

Conclusions

Dosing of radiation affects the outcome of post-BCS radiotherapy in pN1 breast cancer. Doses of over 60.3 Gy_EQD2 were associated with better outcome in the high-risk patients.

Dosimetric comparison of simultaneous integrated boost with whole-breast irradiation for early breast cancer

Purpose

The purpose of this study was to identify a more suitable boost plan for simultaneously integrated boost scheme in patients with breast cancer by comparing among 3 types of whole-breast irradiation plus tumor bed boost plans.

Methods

Twenty patients who received radiotherapy following breast-conserving surgery for early breast cancer were enrolled in this study. We performed 1 type of electron plan (E1P plan) and 2 types of 3-dimensional conformal plans using a photon (P3P and P5P plans). The dosimetric parameters for the heart, total lung and the target volume between the 3 treatment types were compared.

Results

For the tumor bed, the difference in the mean dose between the 3 plans was maximally 0.1 Gy. For normal breast parenchyma, the difference in the mean dose between the 3 plans was maximally 1.1 Gy. In the dose range over the prescribed dose of 51 Gy, V₅₅ and V₆₀ in the E1P plan were lower than those in the P3P and P5P plans, which indicated that the E1P plan was more suitable than the P3P and P5P plans. In case of the heart and total lung, the values of clinically important parameters were slightly higher in the E1P plan than in the P3P and P5P plans. However, these differences were less than 2%.

Conclusion

We observed that a simple electron plan for tumor bed boost is preferable over multi-field photon plans in terms of the target volume coverage and normal tissue sparing.

The Globalization of Cooperative Groups

The National Cancer Institute (NCI)-supported adult cooperative oncology research groups (now officially Network groups) have a longstanding history of participating in international collaborations throughout the world. Most frequently, the US-based cooperative groups work reciprocally with the Canadian national adult cancer clinical trial group, NCIC CTG (previously the National Cancer Institute of Canada Clinical Trials Group). Thus, Canada is the largest contributor to cooperative groups based in the United States, and vice versa. Although international collaborations have many benefits, they are most frequently utilized to enhance patient accrual to large phase III trials originating in the United States or Canada. Within the cooperative group setting, adequate attention has not been given to the study of cancers that are unique to countries outside the United States and Canada, such as those frequently associated with infections in Latin America, Asia, and Africa. Global collaborations are limited by a number of barriers, some of which are unique to the countries involved, while others are related to financial support and to US policies that restrict drug distribution outside the United States. This article serves to detail the cooperative group experience in international research and describe how international collaboration in cancer clinical trials is a promising and important area that requires greater consideration in the future.