For women with early breast cancer, estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative, adjuvant endocrine therapy is the mainstay of systemic treatment. However, some of these cancers also stand to benefit from adjuvant chemotherapy. The magnitude of benefit from chemotherapy depends on the baseline risk of recurrence, which may be estimated from clinical features including the stage and grade of the tumor, as well as biologic features of the tumor, including gene expression.

All women with hormone receptor (HR)-positive, HER2-negative, non-metastatic breast cancer should be offered endocrine therapy.

Most instances of ER-positive, HER2-negative, node-negative breast cancer <1 cm, and all cancers ≤0.5 cm, have a sufficiently good prognosis with endocrine therapy alone, that they do not typically require adjuvant chemotherapy. At the other end of the risk spectrum, most women with stage III breast cancers will warrant adjuvant chemotherapy because of their risk of recurrence and the likely benefits of chemotherapy treatment. The majority of cases of ER-positive breast cancer fall in between these two extremes, and decisions regarding the addition of chemotherapy to adjuvant endocrine therapy are individualized based on patient and disease factors. Using gene expression profiles in women with ER-positive, HER2-negative disease in whom the decision regarding whether or not to use chemotherapy is unclear.

●We typically use these assays in patients with T1b to T3, node-negative tumors.

●Some also use them in patients with limited node-positive disease, although this practice is not uniform.

●However, we do not use these assays in patients with T1aN0 disease, as these patients have an excellent prognosis with endocrine therapy alone; nor do we generally use them in patients with stage III disease, as such patients typically have a high likelihood of benefit from chemotherapy. Exceptions might be made for patients with low-grade tumors and very limited lymph node involvement.

●Finally, as the primary role of these assays is to determine which clinical situations warrant chemotherapy, we do not use these assays in women who are not candidates for chemotherapy as the results would not alter management. This might include patients with absolute contraindications to chemotherapy due to baseline health concerns or frailty, or women who for other reasons will not consider chemotherapy. Gene expression profiles such as the Oncotype DX Recurrence Score (RS), EndoPredict, the Breast Cancer Index, and the Predictor Analysis of Microarray 50 (PAM50) intrinsic subtype assay have been developed to identify patients with such a low chance of recurrence that the absolute benefit of chemotherapy may not justify the risk of toxicities [1]. For the RS, prospective, randomized clinical trials do not demonstrate that women with low scores (less than 26) benefit from the addition of chemotherapy. By contrast, patients with higher scores on these assays have a sufficiently high risk of recurrence despite endocrine therapy that the addition of chemotherapy outweighs the risk of toxicities. Moreover, given that the response to treatment is not uniform among all cancers, these assays may identify those cancers that, based on their biologic profile, are likely to have an excellent outcome with endocrine therapy alone versus those in which the addition of chemotherapy would substantially reduce the risk of recurrence. The Oncotype DX 21-gene Recurrence Score (RS) is the best-validated prognostic assay and may identify patients who are most and least likely to derive benefit from adjuvant chemotherapy. At this time, it is indicated for women with node-negative, estrogen receptor (ER)-positive, HER2-negative breast cancer to determine the prognosis in patients recommended to proceed with at least a five-year course of endocrine therapy. The RS was developed by identifying the 250 most promising candidate genes described in the literature [2]. Investigators then used a reverse transcription polymerase chain reaction (RT-PCR)-based method for generating quantitative expression levels of these genes in fixed tissue from 447 patients collected from three datasets. A mathematic formula that includes 16 genes (plus 5 reference genes) was then generated to optimize prediction of distant relapse despite tamoxifen therapy. The sum of this calculation is known as the RS. The RS has been validated both as a prognostic as well as a predictive tool, by which to identify those patients with node-negative, hormone receptor (HR)-positive breast cancer whose prognosis is so favorable that the absolute benefit of chemotherapy is likely to be very low. Patients with ER-positive cancers that are node negative derive substantial benefit from chemotherapy if the 21-gene RS is high (typically >25). By contrast, if the score is low or midrange (≤25), there is no benefit to adding chemotherapy to endocrine treatment for women >50 years old, although younger women may experience some benefit [4,5,6].

The RS has been prospectively validated as a prognostic tool [6,7,8]. For example, the TAILORx study evaluated outcomes in 9719 women with HR-positive, HER2-negative, axillary node-negative breast cancer [4,6,7]. At nine years:

Among approximately 1600 women with low RS (≤10), all of whom received endocrine therapy without chemotherapy, the rate of invasive disease-free survival (DFS) at nine years was 84 percent [4].

●Among 6700 women with midrange RS (11 to 25), those randomly assigned to endocrine therapy alone had the same invasive DFS outcomes as those randomized to chemotherapy and endocrine therapy (83 versus 84 percent at nine years; hazard ratio [HR] 1.08, 95% CI 0.94-1.24) [4]. Rates of distant recurrence and overall survival (OS) were also similar between both groups (95 and 94 percent, for endocrine versus chemoendocrine therapy, respectively).

●Among almost 1400 women with a high RS (≥26), all of whom received chemotherapy (typically taxane- and/or anthracycline-containing regimens), the invasive disease free survival was 76 percent at nine years, and the rate of freedom from distant recurrence was 87 percent [4,9]. These results are better than what has been observed in other trials of endocrine therapy alone in similar patients (60 to 70 percent for invasive distant recurrence free survival rates, in the initial validation studies of the RS assay) [2,10]. Observational data also support an OS benefit for the addition of chemotherapy to endocrine therapy in this subset [11].

The overall results from TAILORx are similar to those from the PlanB trial [6], as well as earlier retrospective evaluations of the National Surgical Adjuvant Breast and Bowel Project (NSABP) B-20 clinical trial specimens (“prospective-retrospective” studies) [3]. In this trial of 651 patients, the addition of cyclophosphamide, methotrexate, plus fluorouracil (CMF) to tamoxifen resulted in a higher rate of distant DFS at 10 years among patients with a high RS (>30) compared with treatment with tamoxifen alone (88 versus 60 percent, respectively; relative risk 0.26, 95% CI 0.13-0.53) [3]. However, there was no evidence of a benefit with the addition of CMF among those with a low (<18) or an intermediate RS (19 to 30). It should be noted that the cutoff for low, intermediate, and high RS differed between the TAILORx and NSABP B-20 studies.

It has been argued that RS can be supplanted by improvements in pathologic grading and quantitative HR scoring. However, the NSABP B-20 study suggests that this may not be true. Even with central laboratory grading, 19 percent of high-grade tumors had a low RS (<18) and 5 percent of low-grade tumors had a high RS (>30). Further, the reproducibility of estrogen receptor (ER) and progesterone receptor (PR), as well as measures of proliferation such as immunohistochemistry (IHC) analysis of Ki-67, is poor between different laboratories.
Special considerations for those with intermediate RS — For women of any age whose tumors have a Recurrence Score (RS) ≤15, or for those >50 years with an RS ≤25, we recommend not using chemotherapy. Experts are divided in regards to the approach for patients ≤50 years with node-negative cancers with RS between 16 and 25. Some note that for most such patients they would not treat with chemotherapy, instead offering endocrine therapy alone and adding ovarian suppression for patients who are premenopausal. Other experts, however, offer chemotherapy to select women ≤50 years with RS 16 to 25, especially those who have either high-intermediate scores (21 to 25) or clinical risk factors, based on subset analyses of TAILORx discussed below [12].

In TAILORx, in the subset of women ≤50 years, endocrine therapy plus chemotherapy was associated with a lower rate of distant recurrence relative to endocrine therapy alone if the RS was >15 (at nine years, absolute percentage-point difference was 1.6 for RS 16 to 20, and 6.4 for RS 21 to 25). This benefit was not observed among women >50 years or in the overall population.

In subsequent reporting of TAILORx, clinical-risk stratification was used with the RS [13]. Low clinical risk was defined as tumors ≤3 cm and low grade, ≤2 cm and intermediate grade, or ≤1 cm and high grade. Tumors that did not fit any of these categories were high risk. The level of clinical risk was predictive for a benefit from chemotherapy in the subset of patients ≤50 years with an RS of 16 to 20. Among these women, there was a decrease in distant recurrence rates with versus without chemotherapy among those with high clinical risk (5.5 versus 12 percent, respectively), but not with low clinical risk (4.6 versus 4.8 percent, respectively). When analyzing the data for the entire group of women with intermediate RS (11 to 25), clinical risk did not predict benefit from chemotherapy, irrespective of age. Furthermore, among women ≤50 years with an RS of 21 to 25, the benefit of chemotherapy was similar in the low- and high-clinical-risk subgroups (absolute chemotherapy benefit of 6.4 versus 8.7 percent, respectively).

Among premenopausal women, the benefit from chemotherapy in patients with intermediate RS in TAILORx peaked for those at age 45 years, and the benefit was less for menopausal women. This trend raises the hypothesis that the benefit with chemotherapy in premenopausal women with intermediate RS may be due to chemotherapy-induced premature menopause. (Women younger than 45 years are unlikely to go into a permanent menopause because of chemotherapy and women older than 45 years are more likely to be entering menopause irrespective of chemotherapy. At an age of approximately 45 years, women receiving chemotherapy are most likely to experience menopause due to the chemotherapy)

Some experts support this hypothesis, and therefore offer ovarian suppression rather than chemotherapy for premenopausal women with intermediate RS scores. Others, however, believe that further data are needed, especially in light of the meta-analysis by the Early Breast Cancer Trialists’ Cooperative Group (EBCTCG) with 100,000 randomized patients that does not show any effect of age (or size, grade, stage, or ER status) in the relative benefit from chemotherapy [14]. In a subsequent EBCTCG meta-analysis evaluating dose-intense/dose-dense versus standard every-three-weekly chemotherapy with 37,000 randomized patients, a similar relative benefit with chemotherapy was demonstrated, independent of age and clinical risk factors [15]. However, these meta-analyses were conducted in unselected patients, and not in the intermediate RS group, and pathologic assessment was not performed centrally. Given different interpretations of available data, we recognize that differences in approach among experts exist.

The Amsterdam 70-gene prognostic profile was one of the first gene expression arrays approved for commercial use (MammaPrint). Although it was originally approved for use with unfixed, frozen tissue, it has now been adapted for use with formalin-fixed, paraffin-embedded tissue. Based on the randomized trial discussed below (MINDACT), ASCO has suggested MammaPrint is one of several assays that might be used to determine prognosis for those with high clinical risk, HR-positive, HER2-negative breast cancer and no or limited (one to three) involved lymph nodes to inform decisions regarding withholding chemotherapy [12,16]. However, those with low clinical risk are unlikely to benefit from chemotherapy regardless of the results of this assay. For those with lymph node involvement and a low risk by Amsterdam genetic profile, counseling should be provided that a benefit from chemotherapy cannot be excluded, particularly in patients with more than one involved lymph node.

The 70-gene-profile was developed using a supervised DNA microarray analysis of gene expression arrays on frozen tissue from 98 primary breast tumors [17]. A mathematic model is used to calculate a score that stratifies patients as having a breast cancer with an associated poor prognosis or good prognosis.

The clinical validity of the 70-gene prognostic profile has been demonstrated in multiple studies [18-22]. Results from an international randomized trial, the Microarray in Node-Negative Disease

May Avoid Chemotherapy (MINDACT) trial, suggest that this genetic profile may identify subsets of patients who have a low likelihood of distant recurrence despite high-risk clinical features [22,23]. In this trial, 6693 women, approximately 80 percent of whom had lymph node-negative disease (and 20 percent of whom had one to three positive lymph nodes), underwent risk assessment by clinical criteria (using Adjuvant! Online) and by the 70-gene profile. Patients with discordant clinical and genomic predictions were randomly assigned to receive or not receive adjuvant chemotherapy. Among patients in the intention-to-treat population who had a high clinical risk of recurrence but a low risk by Amsterdam genetic profile, the five-year distant metastases-free survival rates were similar with and without chemotherapy (95.9 versus 94.4 percent, respectively; HR for distant metastasis or death 0.78, 95% CI 0.50-1.21), suggesting that this profile might identify patients with high clinical risk who may reasonably forego chemotherapy. However, it should be noted that the MINDACT study was not powered to exclude a benefit of chemotherapy.

Observational studies have similarly suggested that the 70-gene profile identifies patients with a low chance of recurrence, independent of nodal status, tumor grade, or hormone or HER2 receptor status [24].

There are more limited data for use of gene expression profiles in lymph node positive disease. Although both the Amsterdam 70-gene profile (MammaPrint) and Oncotype DX Recurrence Score (RS) have been evaluated in node positive disease, data for both are limited in this setting. The approach to incorporating gene expression profiles among those with lymph node involvement is variable among experts.

Some do not utilize gene expression profiles in the setting of lymph node involvement and recommend chemotherapy for any involved lymph nodes; others apply the RS for those with one to three lymph nodes and offer chemotherapy for more involved lymph nodes; while others apply RS to those with very limited nodal disease and offer chemotherapy to those with greater lymph node involvement. As such, one may opt for any of the following approaches, taking into account the pros and cons of each strategy.

●Administer chemotherapy to those with lymph node-positive disease.

If choosing this approach, one does not assess RS, as it does not change management. This approach may represent overtreatment and corresponding toxicity for the majority of patients in this category, in an effort to avoid missing patients who could have benefited if they were treated. Supporting rationale and data are as follows.

Adjuvant chemotherapy appears to provide a relative risk reduction in breast cancer mortality of approximately 20 to 30 percent, irrespective of size, stage, grade, estrogen receptor (ER) status, and whether patients were given endocrine therapy, according to the Early Breast Cancer Trialists’ Cooperative Group (EBCTCG) meta-analyses of 100,000 and 37,000 patients [14,15]. Traditionally, lymph node positivity has been thought to confer a worsened prognosis, with lymph node-positive cancers having almost a twofold increase in recurrence rates compared with lymph node-negative cancers, in the absence of chemotherapy. Therefore, given the higher absolute likelihood of recurrence in those with lymph node-positive disease, the absolute benefit of chemotherapy is higher in this subset, and therefore chemotherapy is offered.

●Apply the RS for those with one to three positive nodes, using cutoffs as for those with node-negative disease, and recommend chemotherapy to those with >3 lymph nodes involved.

The rationale for this approach is that, in the modern era of more effective local and adjuvant therapy (eg, aromatase inhibitors, bisphosphonates), lymph node positivity might not confer the same degree of heightened risk as it once did, and that trials in node-negative cancers have not shown benefit from chemotherapy in tumors with low RS. As such, the absolute benefit of chemotherapy may be less than previously thought. Moreover, contrary to the EBCTCG meta-analysis discussed above, data from the neoadjuvant setting suggest that chemotherapy may not provide as much of a benefit for those with estrogen receptor (ER)-positive, HER2-negative disease [59]. This approach is included in the American Society of Clinical Oncology guidelines and in the National Comprehensive Cancer Network guidelines [10,60].

It stands to reason, therefore, that one may identify a subset of patients with lymph node-positive disease (as in those with node-negative disease) whose prognosis is so good that even if chemotherapy reduces the relative risk by 20 to 30 percent, the absolute benefit would still be no more that 1 to 3 percent. This is approximately the risk of severe or life-threatening toxicity of chemotherapy, and therefore it would be reasonable to avoid chemotherapy in such a subset, if it were able to be identified.

Supporting data for using the RS in lymph node-positive disease to identify this good-prognosis subset are limited, but are as follows. In the PlanB study, among 348 patients with RS ≤11 (approximately 40 percent of whom had one to three involved lymph nodes and the rest of whom had node-negative disease), the three-year progression-free survival was 98 percent, after a median follow-up of 35 months [14]. Although subset analysis for patients with node-positive, low-RS cancers was not provided, the overall results suggest that patients with limited nodal disease may be able to avoid chemotherapy if the RS is low. Additionally, a retrospective study evaluated tumor specimens from 367 postmenopausal women with node-positive, hormone receptor (HR)-positive breast cancer randomly assigned to tamoxifen alone or six cycles of cyclophosphamide, doxorubicin, and fluorouracil (CAF) followed by tamoxifen [61]. Compared with tamoxifen alone, the addition of CAF among women with a high RS (>30) resulted in improvements in disease-free and overall survival. By contrast, among postmenopausal women with node-positive tumors and a low RS (<18), no benefit for chemotherapy treatment was observed.

●Employ a hybrid approach, such as applying the RS only for those with a single positive node with <5 mm deposit and no extracapsular extension, using cutoffs as for those with node-negative disease, and recommend chemotherapy to those with more substantial lymph node involvement.

Although there are no specific data to support a hybrid approach and specific size of deposits, etc, this clinical stratification approach attempts to minimize the risks of toxicity with overtreatment, and the risks of recurrence associated with undertreatment.

The SWOG S1007 RxPONDER trial, which utilizes the RS to assign HR-positive, HER2-negative, node-positive patients to standard endocrine therapy with or without adjuvant chemotherapy, is ongoing and will inform our approach.

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STYLIANOS GIASSAS
MEDICAL ONCOLOGIST
CHIEF OF THE 2nd ONCOLOGY CLINIC
IASO HOSPITAL