The addition of new biomarkers for establishing a prognosis for patients with breast cancer has been recommended in the 2010 edition of the American Joint Committee of Cancer’s Cancer Staging Handbook.1 Human epidermal growth factor receptor type 2 (HER2) status and multigene signature “scores” have been added to estrogen receptor (ER) and progesterone receptor (PR) determinations.1 So, where are we regarding multigene signature scores? At this time, two tests are commercially available in the United States: Oncotype DX (Genomic Health) and MammaPrint (Agendia).
21-gene recurrence score assay Available since 2004, Oncotype DX uses a process called reverse transcriptase polymerase chain reaction (RT-PCR) to look at 21 genes: 16 are linked to breast cancer and five are reference genes used for normalizing the expression of the cancer related genes. The chosen genes have demonstrated a consistent statistical link to distant breast cancer recurrence (Figure 1)2 as well as to the degree of response to chemotherapy (Figure 2).3 An algorithm is used to calculate a “recurrence score” (RS) from the expression results for each of 16 cancerrelated genes. The RS ranges from zero to 100. Cutoff points for RS risk groups are defined: low risk, <18; intermediate risk, 18 to 30; and high risk, ≥31. The RS provides information that is independent from age, size, and grade of the tumor.2 This information helps tailor treatment for the individual patient. In addition, the RS is a more significant predictor of distant recurrence-free survival independent of age and tumor size.2 Assigning Individualized Options for Treatment (Rx), a multi-institutional trial known as TAILORx, aims to determine, more specifically, how predictive the assay is for the intermediate-risk RS group.4 The manufacturer has Clinical Laboratory Improvement Amendments certification, and strictly adheres to College of American Pathology standards.
The 21-gene assay is for use in patients with stage I or II, node-negative, ER-positive breast cancer who will be treated with hormone therapy. In 2007, the assay was included in the 2007 American Society of Clinical Oncology clinical guidelines on the use of tumor markers in breast cancer.5 In 2008, the National Comprehensive Cancer Network incorporated the assay into its breast cancer clinical practice guidelines.6 These inclusions reinforce the significance of molecular diagnostics in breast cancer treatment planning and, in particular, the potential value of the individualized information provided.
After the assay became available to clinicians, the manufacturer discovered that 4% to 6% of specimens sent for testing that were ER-positive on immunohistochemistry (IHC) staining were not ER-positive by RT-PCR. In addition, 9% to 20% of specimens that were ER-negative by IHC were ER-positive by RT-PCR. This raised concern: Are there women who could benefit from hormone therapy who are not being identified? To answer this question, the company started including individual quantitative ER, PR, and HER2 scores as part of its reports in 2008. It now offers an ER qualifier program to guide decisions on testing specimens, based on medical necessity as determined by the referring physician, if the ER status by IHC is in question.
Recently presented information suggests increased applications for the 21- gene assay. Three studies have shown that it is also informative for women with node-positive, hormone receptor (HR)-positive, invasive breast cancer. Goldstein and colleagues looked at the prognostic ability of the assay in HRpositive operable breast cancer with one to three positive nodes. They found that a low RS is predictive of an excellent outcome at 5 years, and that a low RS is a common finding in these patients (49%).7 The researchers suggested that patients with a low RS might be candidates for a shorter course of chemotherapy, plus hormonal therapy; and that a high score may be used to select patients who need more aggressive chemotherapy or who would be candidates for clinical trials evaluating novel agents.7
Dowsett and colleagues, on behalf of the Arimidex, Tamoxifen, Alone or in Combination (ATAC) Trialists’ Group, presented a follow-up study referred to as transATAC at the San Antonio Breast Cancer Symposium in 2008.8 They looked at the risk of distant recurrence using the 21-gene assay in postmenopausal breast cancer patients with and without positive nodes who were treated with either tamoxifen or anastrozole, an aromatase inhibitor. Previously, the RS score had only been validated in patients treated with tamoxifen; in the present day, an aromatase inhibitor is usually the endocrine treatment of choice in postmenopausal women. The researchers evaluated 302 node-positive women and 872 node-negative women. They concluded that the RS for women treated with tamoxifen may be applied for those treated with anastrozole with adjustment for the lower risk of recurrence seen with aromatase inhibitors. They further concluded that the RS is an independent predictor of disease recurrence in node-positive as well as node-negative HR-positive patients (Figure 3, page 14).8
Albain and colleagues, on behalf of the Breast Cancer Intergroup of North America, presented results of a retrospective analysis of a randomized study (SWOG 8814) of the prognostic and predictive value of the RS in postmenopausal women with node-positive, ERpositive breast cancer.9 They investigated specifically whether the RS was prognostic in women treated with tamoxifen alone and whether it identified women who could possibly avoid anthracyclinebased chemotherapy (cyclo phosphamide/doxorubicin/fluorouracil [CAF]) despite higher risk of recurrence. This chemotherapy regimen is more “modern” than the regimen of cyclophosphamide/ methotrexate/fluor ouracil used in earlier adjuvant studies. The researchers determined the RS for 367 specimens and found that the RS was prognostic for the group treated with tamoxifen alone. They also determined that CAF therapy had no benefit in patients with a low RS, but that there was an improvement in disease-free survival (DFS) for women with a high RS after adjustment for the number of positive nodes. An improvement in breast cancer–specific survival (BCSS) was also observed for women with a high RS treated with chemotherapy. The 10-year BCSS was 73% compared with 54% for the tamoxifen alone group in the high RS group. The predictive benefit of the RS was significant in the first 5 years only (P = .029); there was no additional prediction beyond this time (P = .58), although there was a cumulative benefit at 10 years (P = .053). The researchers concluded that a low RS identifies women who, despite positive nodes, might not benefit from CAF.9
Based on these results, the Centers for Medicare & Medicaid Services (CMS) extended coverage for Oncotype DX to ER-positive patients with micrometastases and one to three positive nodes.10 An editorial in Lancet Oncology states, “…the consistency across studies suggests that there is little risk of falsely concluding that there is no chemotherapy benefit in patients with low re currence scores.”11
Small studies have been conducted to determine whether the 21-gene assay may help predict response to neoadjuvant therapy. Anderson and colleagues from core biopsies to surgical specimens on more than 11,000 samples. They had a 92% correlative success rate.12 With the confidence that core biopsies provide accurate information, three small studies examined RS and response to neoadjuvant therapy.13-15 Two studies used chemotherapy; one used hormonal therapy. No patients with a low RS had a pathologic complete response (pCR) in the chemotherapy studies; however, these patients had a much better clinical response in the hormonal therapy group. Therefore, assay results may help physicians and patients assess the benefit of neoadjuvant therapy options.
Finally, the usefulness of the 21-gene assay for both physicians and patients has been confirmed in several studies. Based on assay results in node-negative patients, physicians have reported changing their treatment recommendations 20% to 31.5% of the time. The most frequent change is to omit chemotherapy.16-18 At one comprehensive cancer center, the number of patients getting chemotherapy decreased from 55% to 25%.19 More than 80% of patients stated that the results influenced their decisions, and more than 90% were glad they took the test. Patients reported less anxiety and situational conflict.20 Oratz and colleagues polled more than 1000 physicians who ordered the assay for node-positive patients and found that there was a change in chemotherapy recommendation 42% of the time.21
70-gene prognostic signature Available in Europe since 2004, MammaPrint received US Food and Drug Administration (FDA) approval in February 2007. It was the first clearance issued by the FDA for a breast cancer recurrence test based on data that showed that the gene signature adds independent prognostic information to clinicopathologic risk assessment. The test was validated for use in patients less than 61 years of age with stage I or II, node-negative, ER-positive or ER-negative tumors. MammaPrint was developed in an untreated, heterogeneous patient population.22 In June 2007, Agendia also obtained FDA clearance for use of its tissue preservative (RNARetain). It should be noted that there is a difference in FDA approval and FDA clearance. Clearance provides marketing permission for a test that is considered to pose a low risk to public health and that has been shown to be substantially equivalent to another test. Formal approval provides marketing permission for a test that is new or may be of higher risk to the user; studies are evaluated that show the test does what it claims. This 70-gene prognostic signature became commercially available in the United States in 2008.
Using a process called microarray gene chip technology, the test identified 70 genes linked to the genomic pathways associated with breast cancer recurrence. An algorithm was used to establish two gene signatures (Figure 4, page 14). The test uses fresh-frozen tissue or tissue that must be put into a DNA preservative within an hour and then mailed to the manufacturer. It does not provide an individual RS, but rather binary results. A “low-risk signature” or “good prognosis” means a woman has a 95% chance of DFS at 5 years, a 90% chance at 10 years, and a 99% BCSS rate at 5 years. A “high-risk signature” or “poor prognosis” means a woman has a 78% chance of DFS at 5 years, a 71% chance at 10 years, and an 80% BCSS rate at 5 years.22-24
The 70-gene prognostic signature has been found to be of benefit in deciding prognosis in women with node-positive disease. In 2007, Mook and colleagues presented the results from 106 patients with one to three positive lymph nodes.25 They found that the 70-gene signature outperformed clinicopathologic prognostic factors. In patients with a good prognostic score, at 10 years, overall survival (OS) was 99.7% and DFS was 94%. In patients with a poor prognostic score, OS was 66% and DFS was 62%. Based on these results, patients with one to three positive nodes were incorporated into the Microarray in Node Negative and 1 to 3 Positive Lymph Node Disease May Avoid Chemotherapy (MINDACT) trial to obtain prospective validation.25 MINDACT is a prospective, randomized trial being conducted by an international breast group (TRANSBIG) comparing the 70-gene signature with the common clinicopathologic criteria in selecting breast cancer patients with zero to three positive nodes for adjuvant chemotherapy.26
In addition, in 2009, Saghatchian and colleagues reported an analysis of frozen tumor samples from 519 node-positive patients followed for 10 years. They found the 70-gene signature to be a strong prognostic marker of disease recurrence and BCSS. Patients with a high genomic risk and elevated number of positive lymph nodes (more than three) have a very poor prognosis; therefore, the researchers suggested that these patients may want to consider more aggressive treatment.27 Based on these results, CMS provides coverage for the 70-gene prognostic signature for all patients with stage I and II breast cancer, including those with one to three positive nodes.10
CMS coverage for the 70-gene signature has also been expanded to include all age groups. Bedard and colleagues looked at 204 women aged 65 years and older (median, 70 years). They found that the 70-gene signature remained an independent prognostic indicator in this group.28 Data were confirmed in a group of patients between 55 and 70 years of age.29
Finally, studies have been reported showing the predictive value of the 70-gene signature. Although there has been no prospective analysis of the predictive value of this test in randomized, controlled, phase 3 trials, Knauer and colleagues presented data at the 2009 St. Gallen Breast Cancer Conference on a meta-analysis of 1637 tumor samples of women who received adjuvant chemotherapy plus hormonal therapy or hormonal therapy alone for T1-3, N0-1, M0 breast cancers. This was a heterogeneous group of women: ER-positive, ER-negative, HER2-positive, and HER2-negative. Median follow-up was 7.1 years. Data on 167 neoadjuvant chemotherapy patients were also reviewed. The researchers found that the 70-gene prognostic signature was predictive of neoadjuvant and adjuvant therapy. For low-risk patients, chemotherapy plus hormonal therapy did not demonstrate a significant benefit compared with hormonal therapy alone; however, there was a clear benefit in high-risk patients. In patients who received neoadjuvant therapy, there was no pCR in low-risk patients, but there was a 20% pCR in high-risk patients.24,30,31
Agendia can also provide geneexpression levels of the ER, PR, and HER2 in freshly preserved tumor biopsies using a high-density microchip assay called TargetPrint. TargetPrint has been validated against FDA-approved IHC assays. It can be ordered with or without ordering MammaPrint.
Conclusion The additional information about the clinical behavior of a patient’s cancer provided by these assays should help the clinician in personalizing a therapeutic program for patients. Hopefully, fewer patients who will not benefit from chemotherapy will be exposed to the toxicity of these agents.
Disclosure Ms Dell is a member of Genomic Health’s speakers’ bureau. References
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