The majority of newly diagnosed patients with early-stage breast cancer present with hormone receptor (HR)–positive, lymph node–negative disease. While endocrine therapy and adjuvant chemotherapy are undisputed evidence-based treatment options for this patient population, determining which patients actually benefit from additional chemotherapy represents a clinical challenge. Assessment of recurrence risk is an integral component of clinical decision-making regarding optimal recommendations of systemic adjuvant therapy and the necessity of chemotherapy. However, classical clinicopathologic and immunohistochemical parameters such as nodal involvement, tumor size, and histologic grade are inadequate for decision-making in the adjuvant treatment of early-stage breast cancer, often leading to overtreatment or undertreatment of patients, thus highlighting the need for more robust and practical means of risk assessment.

Considering the heterogeneity of breast cancer, a genomic approach utilizing gene expression profiling to provide valuable information on the underlying biology of breast cancer and its recurrence potential has emerged. This approach provides accurate and clinically useful prognostic information and, in the case of some profiles, can predict benefit from chemotherapy. Several genomic assays have been developed to predict risk of recurrence for early-stage breast cancer. The most commonly utilized among these are the 21-gene recurrence score (RS) assay (Oncotype DX^®) and the 70-gene signature (MammaPrint^®), which measure gene expression levels within the tumor to produce number scores that correlate with the risk of disease recurrence.

Current Treatment Recommendations Integrating Multigene Assays
Based on the current clinical evidence, Oncotype DX is now included in the American Society of Clinical Oncology (ASCO) guidelines for the use of tumor markers in breast cancer to predict risk of recurrence in patients considering treatment with tamoxifen and to identify patients who might not require adjuvant chemotherapy, as well as those with high risk of recurrence who might need adjuvant chemotherapy.¹ The National Comprehensive Cancer Network (NCCN) Clinical Practice Guidelines in Oncology™ for breast cancer also suggest the use of Oncotype DX in patients with HR-positive, HER2-negative, node-negative, or micrometastasis-involved disease to help guide chemotherapy treatment decisions.² The NCCN recommends adjuvant chemotherapy for patients with breast cancer based on tumor stage, HR status, and HER2 status. It does not recommend chemotherapy to patients with estrogen receptor (ER)–positive tumors >1 cm in diameter with a low RS (<18) since endocrine therapy alone might be sufficient in these patients. The recommendations of the 2009 St Gallen International Expert Consensus on primary therapy of early breast cancer are similar to those of the NCCN but do not specify the type of gene expression profiling test to use for decision-making regarding chemotherapy in patients with HR-positive tumors.³ The National Cancer Institute (NCI) treatment guidelines do not mention gene expression profiling at all. However, they recommend adjuvant chemotherapy for all patients with stage I breast cancers >1 cm in diameter, but not for patients with HR-positive, grade 1 tumors <1 cm.⁴

Ongoing Trials Evaluating Multigene Assays
Thus far, the utility of Oncotype DX and MammaPrint has only been evaluated and established from retrospective studies. Recognizing the need for validating these results from prospective, randomized, large studies, several research groups are conducting large phase III trials to prospectively evaluate the utility of integrating Oncotype DX results and MammaPrint results into the clinical decision-making process.

The randomized phase III TAILORx (Trial Assigning Individualized Options for Treatment) trial, developed by the North American Breast Cancer Intergroup, is currently evaluating the best individual therapy for patients with node-negative, ER-positive, stage I/II breast cancer using Oncotype DX. In particular, this trial addresses the clinically important question of whether patients falling in the intermediate-risk group benefit from chemotherapy. In this trial, patients considered low-risk (RS <11) will receive hormone therapy alone, and patients considered high-risk (RS >25) will receive hormone therapy plus chemotherapy, while patients with intermediate risk (RS 11-25) will be randomized to receive hormone therapy with or without the physician's choice of chemotherapy.⁵ (Figure 1) This practical trial design capitalizes on the fact that sufficient evidence exists to make definitive treatment recommendations for the low-risk and high-risk groups (to receive hormone therapy and chemotherapy, respectively), while identifying the intermediate-risk group as the experimental group of patients. It is notable that, in efforts to decrease the potential for undertreatment in the high-risk and intermediate-risk groups, the RS ranges of the risk categories in the TAILORx trial were redefined from those originally outlined as low-risk (<18), intermediate-risk (18-30), and high-risk (≥31) RS ranges.^6,7 A range of RS 11-25 was chosen because when the linear fit of the likelihood of distant recurrence was analyzed as a continuous function of RS in the B20 trial, a trend favoring addition of chemotherapy became apparent at RS 11 and extended until RS 28.⁸ Further, the rationale for the TAILORx definitions are supported by the distribution of RS ranges in the post-marketing experience. The TAILORx trial recently completed accrual and is expected to complete final data collection for primary outcome measures in 2014.

Figure 1. TAILORx trial: Trial design⁵

The Plan B trial has been initiated by the West German Study Group (WSG) to assess whether gene expression–based prognostic assays may prevent overtreatment with adjuvant chemotherapy of patients with high-risk breast cancer.⁹ In this trial, patients are defined as high-risk by node-positive disease or tumor size >2 cm, grade 2-3, age <35 years, high uPA/PAI-1, or HR-negative in N0 patients. All patients with HR-positive disease with 0 to 3 involved lymph nodes will undergo mandatory prospective risk-stratification using Oncotype DX (+ uPA/PAI-1). Patients with 0-3 positive lymph nodes and low a RS of <11 will receive endocrine therapy only. (Figure 2) A proposed 2448 patients with RS >11 will receive chemotherapy, either anthracyline-free taxane-based chemotherapy or an anthracycline-taxane–based chemotherapy. The primary study endpoint of the trial is disease-free survival (DFS); secondary endpoints include comparison of overall survival (OS) and toxicity in the experimental arms. At the 2010 ASCO-NCI-EORTC Annual Meeting on Molecular Markets in Cancer, Salem et al reported that 1067 patients at 96 centers have been randomized. Of the 298 evaluable patients, 21% had RS of 0-11, while 59% had RS 12-25, and 20% had RS >25.¹⁰

Figure 2. West German Study Group Plan B trial: Trial design⁹
Abbreviations: AGO, German Working Group for Gynaecological Oncology; HR, hormone receptor; LN, lymph node; RS, recurrence score.

A GEICAM (Spanish Group of Breast Cancer Research) study is also prospectively evaluating the impact of Oncotype DX on adjuvant treatment decisions for patients with early-stage breast cancer.¹¹ One hundred seven patients with node-negative, ER-positive, HER2-negative breast cancer were offered either endocrine therapy or endocrine therapy plus chemotherapy. The study found that RS results changed treatment recommendations for 31.8% of patients, with 21% of these patients switching from an initial plan of chemotherapy plus endocrine therapy to endocrine therapy alone. The study also reported that, in 61% of cases, the oncologists' confidence in their treatment decisions increased with integration of Oncotype DX into their clinical practice.

MINDACT (Microarray in Node-Negative Disease May Avoid Chemotherapy Trial) is a prospective randomized study comparing the prognostic utility of MammaPrint with that of the common clinical-pathologic criteria of Adjuvant! Online in selecting patients for adjuvant chemotherapy of breast cancer that is either node-negative or with ≤3 positive lymph nodes.¹² Following risk-stratification of the estimated 6000 patients using both MammaPrint and Adjuvant! Online assessment, patients with a low risk (estimated in 10% of patients) or high risk (estimated in 10% of patients) of recurrence by both the methods receive either no chemotherapy or chemotherapy. (Figure 3) However, the patients with contradictory prognoses (estimated in 55% of patients) from the two tools will be randomly assigned to receive chemotherapy based on the prognosis from Adjuvant! Online or MammaPrint. Patients with HR-positive disease will receive endocrine therapy. The choice of Adjuvant! Online to assess the common clinical-pathologic criteria is controversial, partly owing to concerns that it is inaccurate and that it underestimates the risk of breast cancer, particularly in cases relating to known prognostic factors such as ER and HER2 status. Two additional questions that will be evaluated in this trial relate to the type of adjuvant chemotherapy (anthracycline-based regimens vs docetaxel-capecitabine regimen) and the schedule of adjuvant endocrine therapy (2 years of tamoxifen followed by 5 years of letrozole vs 7 years of letrozole).¹³

Figure 3. MINDACT trial: Trial design¹²

Conclusions
A substantial body of evidence has accumulated to support the prognostic and predictive utility of multigene assays in clinical decision-making regarding risk of recurrence and benefit from adjuvant chemotherapy in patients with HR-positive, node-negative breast cancer. Results from ongoing prospective trials will help identify patients with early stage breast cancer for whom adjuvant hormonal therapy alone is sufficient, thus obviating the empiric use of chemotherapy in women who do not benefit from it. Individualized therapy using such gene expression modalities heralds an era of personalized medicine that will allow clinicians to make informed decisions regarding the most appropriate treatment options for each patient.

MORE ABOUT GENOMIC ASSAYS FOR EARLY BREAST CANCER

Oncotype DX 21-Gene Recurrence Score Assay
Prognostic utility
Using reverse transcriptase polymerase chain reaction (RT-PCR) on paraffin-embedded breast cancer tissue, Oncotype DX determines the expression of 16 cancer-related genes and 5 reference genes.⁶ These prognostic genes were identified from tumor samples of 447 patients with node-negative, ER-positive breast cancer from three independent clinical studies including 233 patients treated with tamoxifen in the National Surgical Adjuvant Breast and Bowel Project (NSABP) B-20 trial, which compared adjuvant tamoxifen with chemotherapy in node-negative, ER-positive breast cancer. In addition, 78 samples from patients considered high-risk with ≥10 positive nodes, and 136 samples from patients considered lower-risk from clinical centers were included in the analysis.^14,15 The panel of cancer-related genes includes 5 genes in the proliferation group, 2 in the HER2 group, 4 in the ER group, 2 in the invasion group, and 3 other unaligned genes. In node-negative, ER-positive breast cancer, the RS categorizes the risk of distant recurrence as low (RS <18), intermediate (RS 18-30), or high (RS ≥31).

The clinical validation of the Oncotype DX was first tested on tissue samples from patients with ER-positive, node-negative breast cancer who were enrolled in the landmark placebo-controlled NSABP B-14 study, which established the efficacy of tamoxifen.⁶ Oncotype DX assigned 51%, 22%, and 27% of patients into low-risk, intermediate-risk, and high-risk categories, respectively, which were associated with rates of distant recurrence at 10 years by Kaplan-Meier estimates of 6.8%, 14.3%, and 30.5%, respectively. (Figure 4) Only Oncotype DX and poor tumor grade were found to be independently associated with likelihood of distant recurrence in a multivariate Cox proportional hazards analysis examining all the standard measures including age, tumor size, tumor grade, HER2, and ER expression. Subsequently, the prognostic ability of the assay was also independently validated in samples from patients at community hospitals in a Kaiser Permanente study.¹⁶ The trial was performed using a case-control study design in 4964 patients with node-negative breast cancer who did not receive adjuvant chemotherapy. The 10-year absolute risk of breast cancer death in patients with ER-positive disease who were treated with tamoxifen was 2.8%, 10.7%, and 15.5% in the low RS, intermediate RS, and high RS groups, respectively. These results strongly validated Oncotype DX as a predictor of recurrence in patients with node-negative, ER-positive breast cancer.

Figure 4: Clinical validation of Oncotype DX: Distant recurrence in NSABP-14 trial.⁶

The prognostic utility of Oncotype DX was also validated in patients with node-positive breast cancer—a subset of patients that is traditionally considered to be high-risk, thus requiring chemotherapy. In the Eastern Cooperative Oncology Group (ECOG) E2197 trial of endocrine therapy plus doxorubicin/cyclophosphamide or doxorubicin/docetaxel in node-positive or high-risk node-negative breast cancer, Oncotype DX was a significant predictor of 5-year recurrence.¹⁷ In this trial, a significant increase in risk of recurrence was identified for the intermediate RS (hazard ratio [HR], 2.96; P = .0002) and the high RS groups (HR, 4.0; P = .0001) compared to the low-risk group. In the patients with node-positive, ER-positive breast cancer enrolled in the phase III Southwest Oncology Group (SWOG) 8814 trial of tamoxifen with or without cyclophosphamide/doxorubicin/5FU chemotherapy, the Oncotype DX results were significantly prognostic for 10-year DFS (P = .017) and OS (P = .003) in the 148 patients treated with tamoxifen.¹⁸ The 10-year DFS was 60%, 49%, and 43% in patients who were low-risk, intermediate-risk, and high-risk, respectively.

Recently, the results of the transATAC study demonstrated the prognostic utility of Oncotype DX in patients with node-negative and node-positive, HR-positive breast cancer treated with an aromatase inhibitor or tamoxifen.¹⁹ Recurrence score was found to be significantly prognostic in terms of likelihood of distant recurrence for both node-negative and node-positive groups; however, RS was not predictive for benefit from type of endocrine therapy used, ie, tamoxifen or anastrozole. The low RS group with node-positive disease was clearly associated with a better prognosis compared to the high RS group (83% vs 51% distant recurrence-free at 9 years; HR, 2.7; P<.001). While the 9-year risk of distant recurrence for patients with 1-3 positive nodes was slightly higher than that for patients with negative nodes, the risk of distant recurrence was much higher for patients with 4 or more positive nodes. Importantly, the results of this analysis demonstrated that the established relationship between the Oncotype DX results and distant recurrence for tamoxifen could also be extended to aromatase inhibitor anastrozole therapy. Moreover, a combined analysis of pooled tamoxifen-treated patients in the NSABP B-14 and B-20 trials demonstrated that Oncotype DX was significantly associated with locoregional recurrence (LRR; P<.001).²⁰ In this analysis, the 10-year LRR rate was 4%, 7%, and 16% in patients with low RS, intermediate RS, and high RS, respectively.

Prediction of therapy benefit
In addition to estimating risk of relapse, Oncotype DX has also demonstrated the ability to predict benefit from chemotherapy in patients with early-stage breast cancer, which is invaluable for individualizing treatment options for these patients. In the NSABP B-20 trial, patients with high RS showed a 10-year distant recurrence–free survival (DRFS) benefit from tamoxifen plus chemotherapy compared to the DRFS observed in patients receiving tamoxifen alone (88% vs 60%; relative risk [RR], 0.26; P<.001) while no clear chemotherapy benefit was observed for patients with a low RS or intermediate RS.21 (Table 1) These results are consistent with the conclusion that not all patients with node-negative breast cancer benefit equally from adjuvant chemotherapy, and that RS can identify which patients benefit or do not benefit from chemotherapy.

Table 1. Predictive Value of Oncotype DX Recurrence Score for Chemotherapy Benefit in ER-Positive Breast Cancer^18,20

Abbreviations: RS, recurrence score; DFS, disease-free survival; DRFS, distant recurrence-free survival.
^a In the SWOG 8814 trial, patients received sequential chemotherapy and tamoxifen.

Analysis of the SWOG 8814 trial also showed that patients with low risk and intermediate risk as determined by Oncotype DX experienced no DFS benefit from the addition of chemotherapy prior to tamoxifen (P = .97 and P = .48, respectively).¹⁸ (Table 1) In contrast, the patients with high risk who received sequential chemotherapy and tamoxifen had a significantly improved 10-year DFS rate compared to those in the tamoxifen-alone arm (55% vs 43%; P = .033). Similarly, the predictive value of the RS for benefit from anthracycline-based chemotherapy was only apparent in the high-RS group (73% vs 54%; P = .033) and not the low-RS or intermediate-RS group when analyzed in terms of breast cancer–specific survival rate at 10 years.

More recently, a meta-analysis of 1735 patients from the landmark NSABP B-14 and transATAC breast cancer trials demonstrated that a new integrated risk-estimate tool combining Oncotype DX results with traditional pathology and clinical measures (RSPC) supplements the assessment of baseline recurrence risk.²² This prognostic tool was developed with the expectation that it would help decrease the number of patients classified as intermediate risk by RS, and refine distant recurrence risk when RS and pathologic-clinical variables were discordant; it is not intended to predict chemotherapy benefit in early-stage breast cancer.

MammaPrint 70-Gene Signature
The microarray-based MammaPrint is a dichotomous risk-stratifier that is currently approved by the US Food and Drug Administration as a prognostic tool for discriminating between patients at low risk and high risk of distant recurrence in node-negative stage I/IIA breast cancer.²³ This was developed from 78 frozen samples derived from patients under the age of 55 years with node-negative breast cancer, who were treated at the Netherlands Cancer Institute.²⁴ In the updated analysis of these patients at a follow-up of 10 years, the 10-year OS of patients with poor prognosis and good prognosis was 51% and 94% (HR, 10.7; P<.01), respectively. In a retrospective validation of MammaPrint performed in 295 consecutive patients with breast cancer, 10-year OS rates in the 180 patients with poor-prognosis signature and the 115 patients with good-prognosis signature were 55% and 94.5%, respectively, while the risk of distant metastases was 49% and 15%, respectively.²⁵ In patients with node-positive operable breast cancer, the good prognosis–signature group was associated with a better 10-year distant metastasis–free survival (DMFS) (91% vs 76%) and breast cancer–specific survival (BCSS) (96% vs 76%) than the poor prognosis-signature group. Moreover, MammaPrint showed significant superiority compared to conventional prognostic factors in predicting BCSS (HR, 7.17; P = .005).²⁶ The prognostic utility of MammaPrint was further validated in a more recent independent series of patients with node-negative breast cancer.²⁷

MammaPrint demonstrated superiority to the St Gallen and National Institutes of Health (NIH) criteria for risk classification, particularly in accurately identifying patients who are low-risk (40%, 15%, 7%, respectively) who could be spared the morbidity of adjuvant chemotherapy and in identifying patients with risk of distant recurrence. In an independent validation study performed by the TRANSBIG research consortium, MammaPrint outperformed the Adjuvant! Online program, which assesses risk based on conventional clinicopathologic criteria, in terms of time to distant metastasis (HR, 2.32 and 1.68, respectively) and OS (HR, 2.79 and 1.67, respectively).²⁸

MammaPrint was also recently shown to predict chemotherapy benefit in early-stage breast cancer. In a meta-analysis of 541 evaluable patients from 7 clinical studies treated with adjuvant endocrine therapy with or without chemotherapy, MammaPrint clearly demonstrated that the 289 patients with a poor prognostic signature had a significantly worse 5-year distant disease–free survival (DDFS) rate compared to the 252 patients with a good prognostic signature (82% vs 95%; HR, 3.88; P<.01).²⁹ In terms of predicting chemotherapy benefit, patients considered high-risk experienced a significant improvement in DDFS with the addition of chemotherapy to endocrine therapy (88% vs 76%; HR, 0.35; P<.01), while no significant benefit with chemotherapy was found in patients considered low-risk. (Table 2) Concerns have been raised regarding the applicability of MammaPrint in routine clinical practice, owing to low patient numbers in the original studies, heterogeneity in age, diversity in adjuvant systemic therapy used, and other inconsistencies.

Table 2. Meta-Analysis for Predictive Benefit of Chemotherapy with MammaPrint: 5-Year DFS²⁹

Abbreviations: DDFS, distant disease-free survival.

References:

1. Harris L, Fritsche H, Mennel R, et al; American Society of Clinical Oncology. American Society of Clinical Oncology 2007 update of recommendations for the use of tumor markers in breast cancer. J Clin Oncol. 2007;25(33):5287-5312.
2. National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology™: Breast Cancer. V.2.2011. Available at: http://www.nccn.org/professionals/physician_gls/PDF/breast.pdf. Accessed December 7, 2010.
3. Goldhirsch A, Ingle JN, Gelber RD, et al. Thresholds for therapies: Highlights of the St Gallen International Expert Consensus on the primary therapy of early breast cancer 2009. Ann Oncol. 2009;20(8):1319-1329.
4. National Cancer Institute, US National Institutes of Health. Breast Cancer Treatment (PDQ^®). Available at: http://www.cancer.gov/cancertopics/pdq/treatment/breast/healthprofessional. Accessed December 9, 2010.
5. National Institutes of Health. Program for the Assessment of clinical cancer tests (PACCT-1): Trial assigning individualized options for treatment: The TAILORx trial. Clinicaltrials.gov Website. Available at: http://www.clinicaltrials.gov/ct2/show/NCT00310180. Accessed November 19, 2010.
6. Paik S, Shak S, Tang G, et al. A multigene assay to predict recurrence of tamoxifen-treated, node-negative breast cancer. N Engl J Med. 2004;351(27):2817-2826.
7. Sparano JA, Paik S. Development of the 21-gene assay and its application in clinical practice and clinical trials. J Clin Oncol. 2008;26(5):721-728.
8. Paik S, Tang G, Shak S, et al. Gene expression and benefit of chemotherapy in women with node-negative, estrogen receptor-positive breast cancer.J Clin Oncol. 2006; 24(23):3726-3734.
9. National Institutes of Health. Randomised comparison of adjuvant docetaxel / cyclophosphamide with sequential adjuvant EC / docetaxel chemotherapy in patients with HER2/Neu negative early breast cancer. Clinicaltrials.gov Website. Available at: http://clinicaltrials.gov/ct2/show/NCT01049425. Accessed November 19, 2010.
10. Salem M, Gluz C, Liedke S, et al; on behalf of Plan-B Investigators/West German Study Group. Prospectively evaluating recurrence score (RS), uPA/PAI-1, central histopathology, and molecular subtypes regarding risk assessment and efficacy of anthracycline (A)-free chemotherapy (CT) in HER2-negative primary breast cancer (BC): First experiences from WSG Plan B trial. Presented at the 2010 ASCO-NCI-EORTC Annual Meeting on Molecular Markers in Cancer; October 18-20, 2010: Hollywood, Florida. Abstract 67.
11. Albanell J, Colomer R, Ruiz-Borrego M, et al. Prospective transGEICAM study of Oncotype DX^® in clinical decision-making in estrogen receptor-positive, node-negative breast cancer women. Ann Oncol. 2010;21(Suppl 8): Abstract 222PD.
12. National Institutes of Health. MINDACT (Microarray in Node-negative Disease May Avoid Chemotherapy): A prospective, randomized study comparing the 70-gene signature with the common clinical-pathological criteria in selecting patients for adjuvant chemotherapy in breast cancer with 0 to 3 positive nodes. Clinicaltrials.gov Website. Available at: http://www.clinicaltrials.gov/ct2/show/NCT00433589. Accessed November 19, 2010.
13. Cardoso F, Van't Veer L, Rutgers E, et al. Clinical application of the 70-gene profile: the MINDACT trial. J Clin Oncol. 2008;26(5):729-735.
14. Cobleigh MA, Tabesh B, Bitterman P, et al. Tumor gene expression and prognosis in breast cancer patients with 10 or more positive nodes. Clin Cancer Res. 2005;11(24 Pt 1):8623-8631.
15. Esteban J, Baker J, Cronin M, et al. Tumor gene expression and prognosis in breast cancer: multi-gene RT-PCR assay of paraffin-embedded tissue. Proc Am Soc Clin Oncol. 2003;22(850): Abstract 3416.
16. Habel LA, Shak S, Jacobs MK, et al. A population-based study of tumor gene expression and risk of breast cancer death among lymph node-negative patients. Breast Cancer Res. 2006;8(3):R25.
17. Goldstein LJ, Gray R, Badve S, et al. Prognostic utility of the 21-gene assay in hormone receptor–positive operable breast cancer compared with classical clinicopathologic features [published correction appears in J Clin Oncol. 2009;27:3566]. J Clin Oncol. 2008;26(25):4063-4071.
18. Albain KS, Barlow WE, Shak S, et al. Prognostic and predictive value of the 21-gene recurrence score assay in postmenopausal women with node-positive, oestrogen-receptor-positive breast cancer on chemotherapy: a retrospective analysis of a randomised trial. Lancet Oncol. 2010;11(1):55-65.
19. Dowsett M, Cuzick J, Wale C, et al. Prediction of risk of distant recurrence using the 21-gene recurrence score in node-negative and node-positive postmenopausal patients with breast cancer treated with anastrozole or tamoxifen: A TransATAC study. J Clin Oncol. 2010;28(11):1829-1834.
20. Mamounas EP, Tang G, Fisher B, et al. Association between the 21-gene recurrence score assay and risk of locoregional recurrence in node-negative, estrogen receptor–positive breast cancer: results from NSABP B-14 and NSABP B-20. J Clin Oncol. 2010;28(10):1677-1683.
21. Paik S, Tang G, Shak S, et al. Gene expression and benefit of chemotherapy in women with node-negative, estrogen receptor–positive breast cancer. J Clin Oncol. 2006;24(23):3726-3734.
22. Tang G, Cuzick J, Wale C, et al. Recurrence risk of node-negative and ER-positive early-stage breast cancer patients by combining recurrence score, pathologic, and clinical information: A meta-analysis approach. J Clin Oncol. 2010;28(15S): Abstract 509.
23. Sotiriou C, Pusztai L. Gene-expression signatures in breast cancer. N Engl J Med. 2009;360(8):790-800.
24. van 't Veer LJ, Dai H, van de Vijver MJ, et al. Gene expression profiling predicts clinical outcome of breast cancer. Nature. 2002;415(6871):530-536.
25. van de Vijver MJ, He YD, van't Veer LJ, et al. A gene-expression signature as a predictor of survival in breast cancer. N Engl J Med. 2002;347(25):1999-2009.
26. Mook S, Schmidt MK, Viale G, et al. The 70-gene prognosis-signature predicts disease outcome in breast cancer patients with 1-3 positive lymph nodes in an independent validation study. Breast Cancer Res Treat. 2009;116(2):295-302.
27. Bueno-de-Mesquita JM, Linn SC, Keijzer R, et al. Validation of 70-gene prognosis signature in node-negative breast cancer. Breast Cancer Res Treat. 2009;117(3):483-495.
28. Buyse M, Loi S, van 't Veer L, et al. Validation and clinical utility of a 70-gene prognostic signature for women with node-negative breast cancer. J Natl Cancer Inst. 2006;98(17):1183-1192.
29. Knauer M, Mook S, Rutgers EJ, et al. The predictive value of the 70-gene signature for adjuvant chemotherapy in early breast cancer. Breast Cancer Res Treat. 2010;120(3):655-661.