Abstract
Background
In pivotal CDK4/6 inhibitor (CDK4/6i) adjuvant trials, most patients received chemotherapy (CT). However, the role of CDK4/6i in patients spared CT by a genomic signature remains unclear. We investigated the proportion of patients without genomic CT indication but eligible for adjuvant abemaciclib or ribociclib, and estimated their potential benefit from CDK4/6i.
Methods
This retrospective, real-world study included patients with T1–T3, N0–N1, HR+/HER2− early breast cancer (eBC) who underwent Oncotype DX (ODX) testing (2005–2024) at nine Brazilian institutions. Genomic CT indication followed TAILORx and RxPONDER; CDK4/6i eligibility followed MonarchE and NATALEE. Primary endpoints were 5-year invasive disease-free survival (iDFS) and distant disease-free survival (DDFS) among patients eligible for CDK4/6i, without genomic CT indication, treated with endocrine therapy (ET) alone.
Results
Among 922 patients, ODX showed low (<11), intermediate (11–25), and high (>25) genomic risk in 170 (18.4 %), 585 (63.5 %), and 167 (18.1 %), respectively. Overall, 24 (2.6 %) and 120 (13 %) were eligible for abemaciclib and ribociclib, respectively, had no CT indication, and received ET alone. In these patients (median follow-up: 57.8 and 66.4 months), 5-year iDFS and DDFS were 100 %.
Conclusions and relevance
HR+/HER2− eBC patients eligible for CDK4/6i but spared CT by ODX are a minority and have excellent outcomes with ET alone. This highlights the potential benefits of integrating genomic and clinical risk stratification to refine therapeutic decision-making regarding the need for CDK4/6i.
Keywords: Hormone receptor positive early breast cancer, Genomic signatures, Oncotype DX, Cyclin-dependent kinase 4 and 6 inhibitors, Real-world data
Highlights
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A small subset of patients spared CT by ODX was eligible for adjuvant CDK4/6i.
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This clinically relevant subgroup was predominantly postmenopausal.
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CDK4/6i-eligible patients spared CT by ODX had excellent outcomes with ET alone.
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Integrating clinical and genomic risk may refine therapeutic decision-making.
1. Introduction
Despite considerable advances in the management of patients with hormone receptor positive/human epidermal growth factor 2 negative (HR+/HER2–) early breast cancer (eBC), refinements in the indication of treatments such as chemotherapy (CT) and cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) are still required [1].
RxPONDER, in which postmenopausal patients with pN1, T1-3, HR+/HER2– eBC and Oncotype DX (ODX) scores of 0–25 derived no benefit from adjuvant CT, has set a new paradigm in treatment de-escalation [2]. On the other hand, the monarchE trial, which investigated adjuvant abemaciclib added to endocrine therapy (ET) in patients with HR+/HER2– high-risk eBC, showed significant benefits in 5-yr invasive disease-free survival (iDFS) and distant disease-free survival (DDFS) with absolute gains of 7.6 % and 6.7 %, respectively [3]. Additionally, results of the NATALEE trial, which evaluated adjuvant Ribociclib added to ET in patients with N0-1 HR+/HER2– eBC, also demonstrated consistent 3-yr iDFS and DDFS absolute gains of 3.1 % and 2.7 %, respectively [4]. Together, these trials established a new standard of care for most patients meeting their inclusion criteria.
Reconciling these results with the CT de-escalation strategy remains a challenge, as most patients from MonarchE and NATALEE had high clinical risk and received (neo)adjuvant CT in 95.4 % and 88.1 % of cases, respectively. In NATALEE, however, the 3-year absolute iDFS gain from ribociclib within the small CT-untreated subgroup was only 0.8 %, raising doubts about the role of these agents in lower-risk patients [4]. Genomic signatures (GS) – powerful treatment de-escalation tools widely used in clinical practice – were not considered in MonarchE's but were included for selected patients in NATALEE's inclusion criteria. Whether or not patients spared adjuvant CT by a GS could still benefit from adjuvant CDK4/6i treatment is currently unknown.
This study aims to evaluate: 1) the real-world proportion of patients with HR+/HER2– eBC who have low/intermediate risk ODX and are eligible for adjuvant CDK4/6i therapy; and 2) their potential benefit from such treatment.
2. Methods
This multicenter, retrospective cohort study was conducted by Grupo Brasileiro de Estudos em Câncer de Mama (GBECAM) in nine tertiary cancer centers in Brazil, on a dataset of patients with T1-T3, N0-N1, HR+/HER2– eBC and an ODX result between 2005 and 2024.
Clinicopathological and ODX data were collected from medical records. CT indication based on genomic criteria was defined according to the TAILORx trial and the RxPONDER studies. Clinical risk was categorized into low- and high-risk groups using a modified binary classification derived from the Adjuvant! algorithm [5], applied only to stratify CT benefit among patients under 50 years of age with N0 disease, in accordance with TAILORx subgroup analyses [6]. Projections of eligibility for adjuvant CDK4/6i therapy were based on the inclusion criteria from the MonarchE and NATALEE trials.
Patient data are presented in an aggregated and anonymized manner. The study was approved by the Ethics Committee (number 26240819.0.0000.5461), which waived the requirement for informed consent.
To evaluate real-world rate of patients with HR+/HER2– eBC with low/intermediate risk ODX and eligible for CDK4/6i therapy - but who received endocrine therapy alone - a descriptive analysis of the data was performed using absolute and relative frequencies. For survival analyses, 5-yr iDFS and DDFS rates, defined as the time from diagnosis to the first occurrence of invasive recurrence and distant recurrence, respectively, were employed. Follow-up (F/U) time was calculated in months (mo) from the date of diagnosis to the occurrence of the event or censoring. For survival analysis, only patients diagnosed prior to December 2019 were included to ensure a minimum of 5 years F/U.
3. Results
Of 922 patients in the overall cohort, most were over 50 years of age (56.9 %), female (99.1 %) and postmenopausal (55.4 %). 65.7 % of tumors were grade 2, 73.6 % were T1b-c, 79.3 % were node negative (N0) and 70.1 % had low clinical risk disease. 13.2 % were N1 (81.1 % with 1 positive node). ODX indicated low (<11), intermediate (11–25) and high (>25) risk in 170 (18.4 %), 585 (63.5 %) and 167 (18.1 %) patients, respectively. (Table 1).
Table 1.
Baseline characteristics.
| Characteristics | Abemaciclib N = 24 (2.6 %) |
Ribociclib N = 120 (13 %) |
Overall N = 922 |
|---|---|---|---|
| Age | |||
| ≤ 50 yrs | 0 (0 %) | 6 (5 %) | 397 (43.1 %) |
| > 50 yrs | 24 (100 %) | 114 (95 %) | 525 (56.9 %) |
| Sex | |||
| Female | 24 (100 %) | 118 (98.3 %) | 914 (99.1 %) |
| Male | 0 (0 %) | 2 (1.7 %) | 8 (0.9 %) |
| Menopausal status | |||
| Pre | 0 (0 %) | 6 (5.1 %) | 381 (44.6 %) |
| Post | 24 (100 %) | 112 (94.9 %) | 474 (55.4 %) |
| Histology | |||
| IDC | 21 (87.5 %) | 84 (70 %) | 728 (79 %) |
| ILC | 2 (8.3 %) | 27 (22.5 %) | 114 (12.4 %) |
| Histologic grade | |||
| G1 | 1 (4.2 %) | 18 (15 %) | 172 (18.7 %) |
| G2 | 18 (75 %) | 86 (71.7 %) | 606 (65.7 %) |
| G3 | 5 (20.8 %) | 16 (13.3 %) | 144 (15.6 %) |
| LVI | |||
| Negative | 13 (59.1 %) | 75 (64.7 %) | 667 (75.7 %) |
| Positive | 9 (40.9 %) | 41 (35.3 %) | 214 (24.3 %) |
| T stage | |||
| T1a | 1 (4.2 %) | 1 (0.8 %) | 42 (4.6 %) |
| T1b | 5 (20.8 %) | 16 (13.3 %) | 227 (24.6 %) |
| T1c | 11 (45.8 %) | 32 (26.7 %) | 452 (49 %) |
| T2 | 5 (20.8 %) | 66 (55 %) | 192 (20.8 %) |
| T3 | 2 (8.3 %) | 5 (4.2 %) | 6 (0.7 %) |
| N stage | |||
| N0 | 0 (0 %) | 41 (34.2 %) | 731 (79.3 %) |
| N1mic | 0 (0 %) | 7 (5.8 %) | 69 (7.5 %) |
| N1 | 24 (100 %) | 72 (60 %) | 122 (13.2 %) |
| Positive nodes | |||
| 1 node | 20 (83.3 %) | 59 (81.9 %) | 99 (81.1 %) |
| 2 nodes | 3 (12.5 %) | 9 (12.5 %) | 17 (13.9 %) |
| 3 nodes | 1 (4.2 %) | 4 (5.6 %) | 6 (5.9 %) |
| Progesterone receptor | |||
| Negative | 0 (0 %) | 6 (5 %) | 67 (7.3 %) |
| Positive | 24 (100 %) | 114 (95 %) | 855 (92.7 %) |
| Ki67 | |||
| < 20 % | 2 (8.7 %) | 53 (44.5 %) | 486 (54.2 %) |
| ≥ 20 % | 21 (91.3 %) | 66 (55.5 %) | 410 (45.8 %) |
| Clinical risk | |||
| Low | 0 (0 %) | 10 (8.3 %) | 560 (60.7 %) |
| High | 24 (100 %) | 110 (91.7 %) | 362 (39.3 %) |
| Genomic risk | |||
| RS < 11 | 9 (37.5 %) | 39 (32.5 %) | 170 (18.4 %) |
| RS 11-25 | 15 (62.5 %) | 81 (67.5 %) | 585 (63.5 %) |
| RS > 25 | 0 | 0 | 167 (18.1 %) |
| MonarchE cohort | |||
| Cohort 1 | 7 (29.2 %) | NA | NA |
| Cohort 2 | 17 (70.8 %) | NA | NA |
IDC, invasive ductal carcinoma; ILC, invasive lobular carcinoma; LVI, lymphovascular invasion; N0, node negative; N1mic, micrometastatic lymph node involvement; N1, macrometastatic lymph node involvement; RS, recurrence score; NA, not applicable.
In the overall cohort, 629 (68.2 %) did not have genomic indication for CT according to current clinical data and guidelines, and 55 (6 %) and 222 (24.1 %) were eligible for adjuvant abemaciclib and ribociclib, respectively. Of these, 24 (1.8 %) and 120 (10.5 %), respectively, were spared CT in clinical practice and received ET alone.
Baseline characteristics of the abemaciclib- and ribociclib-eligible patients are detailed in Table 1. Among the 24 patients eligible for abemaciclib, all were over 50 years of age and postmenopausal. Of these, 29.2 % met MonarchE cohort 1 criteria, the majority (83.3 %) had only one positive lymph node, and 70.8 % met cohort 2 criteria based on a Ki67 ≥ 20 %, as assessed by local pathology. Among the 120 patients eligible for ribociclib, nearly 95 % were over 50 years of age and postmenopausal. Regarding nodal status, 34.4 % were N0, 5.8 % N1mic, and 60 % N1. Notably, consistent with the overall cohort—which was predominantly postmenopausal (55.4 %)—the abemaciclib- and ribociclib-eligible subgroups who were spared chemotherapy based on ODX results were particularly enriched for patients over 50 years of age and postmenopausal (95–100 %).
In patients with indication for abemaciclib (median F/U: 57.8mo) or ribociclib (median F/U: 63.4mo), 5-yr iDFS and DDFS rates were 100 % (Fig. 1). A single distant recurrence was observed in a patient with low genomic risk at 96 mo of F/U. Additionally, among ribociclib-eligible patients, two locoregional recurrences were documented in patients with intermediate genomic risk at 62 and 66 mo of F/U. The 5-yr overall survival (OS) rates were 100 % in both the abemaciclib- and ribociclib-eligible subgroups.
Fig. 1.
Invasive disease-free survival (iDFS) and distant disease-free survival (DDFS) in patients eligible for abemaciclib and ribociclib and treated with endocrine therapy alone.
4. Discussion
This retrospective, real-world study shows that a minority of patients deemed ineligible for CT based on ODX are candidates for adjuvant abemaciclib and/or ribociclib. However, these same patients had exceptional 5-yr outcomes with ET alone.
Despite the reported benefits from adjuvant abemaciclib and ribociclib, their pivotal trials had limitations. First, OS data are still pending; this is a cause of concern because, in the advanced setting, the SONIA trial showed no significant differences in progression-free survival 2 and OS between early versus delayed introduction of CDK4/6i therapy [7]. Second, the predominant inclusion of patients with high clinical risk which selected a population in which most patients required CT, raising doubts about the role of these agents in the absence of CT [3,4] – a crucial question that is now under investigation by prospective clinical trials [8]. Finally, their inclusion criteria were mainly based on anatomical stage – except for selected NATALEE stage IIA/N0 patients, who were included based on high risk by GS [4]. Yet, patients are now increasingly evaluated for CT indication based on molecular profile rather than anatomic stage [[9], [10], [11], [12]]. Consequently, situations in which patients are spared CT by a GS while meeting the inclusion criteria for adjuvant CDK4/6i are increasingly common in clinical practice [13], rendering clinical decisions challenging.
The WSG-PlanB study, for instance, showed that patients with HR+/HER2–, high clinical risk (pN0-1) and low genomic risk (RS 0–11) have excellent outcomes [5-year DFS and overall survival [OS] of 94 % and 99 %, respectively] under ET alone [11]. Similarly, in the ADAPT trial, pN0-1 patients with either RS < 11 or RS 12–25/ET response had excellent outcomes under ET alone [5-year iDFS of 93.9 % and 92.6 %, respectively], regardless of age and nodal status [12].
As a note of caution, a biomarker study from MonarchE with exome-capture RNA sequencing and paired tumor-normal whole-exome sequencing that inferred 21-gene expression signature showed similar benefits from abemaciclib in low and high-risk groups. However, this exploratory analysis is driven by very high clinical risk features of the predominant cohort 1 (60 % of N2, 20 % of T3 and 40 % G3 tumors), and cannot be applied to cohort 2 and intermediate-high clinical risk populations [14].
This study has limitations, such as its retrospective design, relatively short F/U for a HR+/HER2– patient population and the assessment of pathological anatomy and immunohistochemical features done on a local basis. Its strengths, however, include large sample size, meticulous data curation and multicentric design.
5. Conclusions
Postmenopausal patients with HR+/HER2– eBC eligible for adjuvant abemaciclib or ribociclib but spared CT based on an ODX result constitute a minority of patients in clinical practice and have exceptional outcomes under ET alone. These data highlight the potential benefits of integrating genomic and clinical risk stratification to refine therapeutic decision-making regarding the questionable need for CDK4/6i, minimizing toxicities and saving costs.
CRediT authorship contribution statement
Leandro Jonata de Carvalho Oliveira: Writing – review & editing, Writing – original draft, Supervision, Methodology, Formal analysis, Data curation, Conceptualization. Daniela Dornelles Rosa: Writing – review & editing, Validation. Artur Katz: Writing – review & editing, Validation. Daniele Assad-Suzuki: Writing – review & editing, Validation. Daniel Argolo: Writing – review & editing, Validation. Solange Moraes Sanches: Writing – review & editing, Validation. Laura Testa: Writing – review & editing, Validation. José Bines: Writing – review & editing, Validation. Rafael Aliosha Kaliks: Writing – review & editing, Validation. Debora de Melo Gagliato: Writing – review & editing, Validation. Romualdo Barroso-Sousa: Writing – review & editing, Validation. Tatiana Strava Corrêa: Writing – review & editing, Validation. Andrea Kazumi Shimada: Writing – review & editing, Validation. Carlos Henrique dos Anjos: Writing – review & editing, Validation. Rudinei Linck: Writing – review & editing, Validation. Thais Baccili Cury Megid: Writing – review & editing, Validation, Formal analysis, Data curation. Daniel Negrini Batista: Writing – review & editing, Validation, Data curation. Daniel Musse Gomes: Writing – review & editing, Validation, Data curation. Marcelle Goldner Cesca: Writing – review & editing, Validation, Data curation. Débora Gaudêncio: Writing – review & editing, Validation, Data curation. Larissa Matos Almeida Moura: Writing – review & editing, Validation, Data curation. Julio Antonio Pereira de Araújo: Writing – review & editing, Validation, Data curation. Renata Colombo Bonadio: Writing – review & editing, Validation, Data curation. Zenaide Silva de Souza: Writing – review & editing, Validation, Data curation. Juliana Rodrigues Beal: Writing – review & editing, Validation, Data curation. Mario Machado Lopes: Writing – review & editing, Validation, Data curation. Leticia Telles Sales: Writing – review & editing, Validation, Data curation. Júlia Leal Franco Parisi Marlière: Writing – review & editing, Validation, Data curation. Max Senna Mano: Writing – review & editing, Writing – original draft, Validation, Supervision, Formal analysis, Conceptualization.
Ethics approval
This study was approved by Ethics Committee in Sirio-Libanes Hospital (number 26240819.0.0000.5461) as well as in all institutions included.
Funding
The authors received no funding for this work.
Declaration of competing interest
LO has received honoraria from Fleury, unrelated to this work. LT has received honoraria from Novartis, Roche, Pfizer, Zodiac, Lilly, MSD, Daiichi Sankyo, AstraZeneca, and BeiGene; served on advisory boards for Lilly, Novartis, MSD, Daiichi Sankyo, AstraZeneca, Pfizer, and Roche; received educational support from Pfizer, Libbs, United Medical, Lilly, Zodiac, Daiichi Sankyo, Gilead, AstraZeneca, MSD, and Roche; and institutional research funding from Novartis, all unrelated to this work. JB has received honoraria and/or served on advisory boards for AstraZeneca, Daiichi Sankyo, Exact Sciences, Gilead Sciences, Knight, Libbs, Lilly, MSD, Novartis, Pfizer, and Roche; and received travel grants from AstraZeneca, Daiichi Sankyo, and Gilead, unrelated to this work. DMG has received honoraria from Lilly, Roche, AstraZeneca, Daiichi Sankyo/Lilly, Novartis, and Pfizer; served in advisory roles for Teva, Roche/Genentech, Lilly, Daiichi Sankyo/Lilly, and Pfizer; received research funding from Novartis; and travel support from AstraZeneca, Libbs, and Roche, all unrelated to this work. AKS has received speaker honoraria from Daiichi Sankyo/AstraZeneca, Novartis, Pfizer, Lilly, Gilead Sciences, Roche, and Libbs; served in advisory roles for Daiichi Sankyo/AstraZeneca and Pfizer; and received travel support from Novartis and Daiichi Sankyo/AstraZeneca, unrelated to this work. RCB has received speaker and/or consultancy honoraria from Daiichi Sankyo, Nestlé Health Science, Addium, Gilead, MSD, BMS, AstraZeneca, Aché, Pfizer, Novartis, and Lilly; received financial support for educational activities from AstraZeneca, Daiichi Sankyo, MSD, and Lilly; and institutional research support from Novartis and AstraZeneca, unrelated to this work. All other authors have declared no conflicts of interest.
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