Differences in Treatment Outcomes Between Patients with HER2-Low versus HER2-Zero, Hormone Receptor-Positive Advanced-Stage Breast Cancer Treated with Ribociclib

Background

Metastatic breast cancers (MBC) with no expression of human epidermal growth factor receptor-2 (HER2) are recently classified into two groups; HER2-zero [HER2-immunohistochemistry (IHC) score of 0 (IHC-0)] and HER2-low, defined as those with IHC score of 1+ or 2+ with negative in situ hybridization (ISH) assay. We investigate differences in treatment outcomes between both groups treated with endocrine therapy (ET) and the CDK4/6 inhibitor ribociclib.

Methods

Data were retrospectively collected for patients with HR-positive+/HER2-negative MBC who received ribociclib with an aromatase inhibitor (AI) or fulvestrant and were divided into two groups: HER2-zero and HER2-low.

Results

A total of 257 patients, median age 48 (22-87) years, all with MBC who were treated with ET and ribociclib were enrolled. One hundred and thirty-seven (53.3%) patients had de novo MBC, and majority (n = 162, 63.0%) received ribociclib as a first-line therapy. In total, 114 (44.4%) patients had HER2-zero (IHC-0), while 143 (55.6%) others had HER2-low disease. The overall response rate (ORR) was 52.0% for the HER2-zero group compared to 39.4% for the HER2-low group, p = 0.005. The median PFS was 22.2 (95% confidence interval [CI], 19.4-NR) months for HER2-zero versus 17.3 (95% CI, 14.1-20.6) months for HER2-low, P = 0.0039. In multivariable analysis, HER2-low expression remained significant determinant of inferior PFS after adjusting for other factors, including the site of metastasis, prior chemotherapy, and the line of treatment.

Conclusion

In patients with MBC treated with ET and ribociclib, level of HER2 negativity may affect treatment outcomes; patients with HER2-zero had better response rate and PFS compared to those with HER2-low disease. These findings, if confirmed in larger studies, may help oncologists select patients with HER2-low for better treatment options.

Abstract P4-07-33: Differences in Treatment Outcomes Between Patients with HER2-Low versus HER2-Zero, Hormone Receptor-Positive Advanced-Stage Breast Cancer Treated with CDK4/6 Inhibitors

Background: The cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors transformed the care of patients with hormone receptor-positive (HR+), human epidermal growth factor receptor-2 (HER2)-negative (HR+/HER2−) advanced-stage breast cancer (aBC). Breast cancers with no expression of HER2 are recently classified into two groups: HER2-Zero subtype which include those with HER2-immunohistochemistry (IHC) score of 0 (IHC-0) and “HER2-low”, defined as HER2-IHC score of 1+ or (2+ with negative in situ hybridization (ISH) assay). There is increasing interest in the HER2-low subtype which is becoming a new distinct entity with promising data from recently reported clinical trials using novel anti-HER2 antibody-drug conjugates (ADC) in this subgroup. This study investigates the differences in treatment outcomes between patients with aBC with HER2-low versus those with HER2-Zero (IHC-0) disease treated with CDK4/6 inhibitors and endocrine therapy (ET). Methods: We retrospectively reviewed patients with (HR+/HER2−) aBC who received CDK4/6 inhibitors with an aromatase inhibitor (AI) or fulvestrant from June 2017 to May 2020 at a single cancer center. Data was extracted from patients’ electronic medical records and from our institutional cancer registry. Progression-free survival (PFS), defined as the time from the initiation of CDK4/6 inhibitors to the date of radiological or clinical progression or death, and was estimated by the Kaplan-Meier method and compared by the log-rank test. Multivariate Cox regression modeling was performed with covariates including progesterone receptor (PR) status, prior chemotherapy, site of metastasis (visceral versus bone-only disease), line of treatment (first-line or beyond), menopausal status, age (less than or ≥ 45) and number of metastatic sites (< or ≥ 3). P-value < 0.05 was considered statistically significant. Results: During the study period, a total of 256 patients with advanced-stage breast cancer who received ET and CDK4/6 inhibitors (ribociclib in all patients) were included, median age was 48 (22-87) years. Majority (n=162, 63.3%) received ribociclib as a first-line therapy while the others had it as a second line and beyond. 136 (53.1%) patients had de novo metastatic disease, and 122 (47.7%) were premenopausal. In total, 114 (44.5%) of the patients where HER2-Zero (IHC-0), while 142 (55.5%) others had HER2-low disease as defined above. The overall response rate (ORR) for the HER2-Zero group was 52% versus 39% for the HER2-low group (P= 0.005).The median PFS was 23.0 (95% confidence interval [CI], 19-40) months for HER2-Zero versus 17.0 (95% CI 14-20,) months for HER2-low; P= 0.0035. In multivariate analysis, HER2-low expression remained significant determinant of inferior PFS after adjusting for other factors including the line of treatment (aHR:2.10, 95% CI 1.03-4.27, P=0.041), age (aHR 2.20, 95% CI 1.29-3.77, P=0.004)), number of metastasis (aHR:1.96, 95% CI 1.32-2.91, P=0.001), and site of metastasis (aHR:1.64, 95%CI 1.058-2.55, P=0.027). Conclusion: In patients with advanced-stage breast cancer treated with CDK4/6 inhibitors and ET, level of HER2 negativity may affect treatment outcomes; patients with HER2-Zero had better PFS compared to those with HER2-low disease. These findings, if confirmed in larger studies, should help oncologists select patients with HER2-low for better treatment options including a combination of anti-HER2 therapy and CDK4/6 inhibitors.

Citation Format: Baha’ Sharaf, Hala Abu-Fares, Faris Tamimi, Suhaib Al-Sawajneh, Osama Salama, Rand Daoud, Abdulrahman A. Alhajahjeh, Sawsan Al-lababidi, Hikmat Abdel-Razeq. Differences in Treatment Outcomes Between Patients with HER2-Low versus HER2-Zero, Hormone Receptor-Positive Advanced-Stage Breast Cancer Treated with CDK4/6 Inhibitors [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-07-33.

Abstract P4-06-06: Neoadjuvant B27 protocol in Triple-Negative Breast Cancer: Evaluation response rate, pathological complete response rates,toxicity,and the prognosis of Adolescent and Young Adult (AYA) age group compared to older population

Background: Neoadjuvant chemotherapy (NACT) is the standard early-stage triple-negative breast cancer (TNBC) treatment. Achieving pathological complete response (pCR) is considered an essential prognostic factor with favorable long-term outcomes. Younger patients have with poorer prognosis in breast cancer. To date, few studies are comparing the prognosis of AYA and older women (≥40) with breast cancer subtypes, specifically Triple-negative breast cancer (TNBC), as AYAs had higher proportions of this subtype. Method: Retrospective review was performed on female patients who received NACT at a King Hussien Cancer Center from January 2014 to June 2020. Data were collected from patients’ electronic medical records. TNBC was histopathologically confirmed. Logistic regression analysis of predictors of pathologic complete response (pCR). Survival curves were estimated with the Kaplan-Meier method. Multivariate analysis for EFS was performed using Cox’s proportional hazards regression model, covariates included age at diagnosis (AYA vs. ≥40), tumor size, nodal status LVI and pCR Result: We analyzed 211 women with stage I-III TNBC, including 62 (29.4%) women aged 18 to 39 years (AYA) and 149 (70.6%) ≥40 years. 138 (68.3%) were node positive, and 71 (34.8%) were T3/4 disease. Median follow-up was 28.1 months, median number of ER visit during NAC is 1 (0-11), 23 (10.9 %) patients had admission during neoadjuvant chemotherapy, most commonly due to febrile neutropenia 13 (56.9%). 37 (17.5%) patients did not complete NAC, due to disease progression in 22 (10.4%), and toxicity in 15 (7.1%) patients. 195 (92.4%) patients had surgery, including 75 (35.5%) had breast-conserving surgery (BCS). 166 (76.3%) patients had objective response, and 64 (30.3%) had pCR. 170 (80.6%) received adjuvant radiotherapy, and 38 (18%) received adjuvant capecitabine. No significant differences between the AYA and the ≥40 group in terms of clinicopathological, toxicity, pCR rate, and the rate of BCS. In univariate analysis, the LVI, nodal status, pCR, and age group were significant predictors of DFS. In multivariate analysis, only PCR and age are the only independent predictor of DFS. The median DFS was worse in the AYA population 47.8 (31.21-64.39) months vs. NR in ≥40 (p-value 0.013). In patients who achieved pCR, the estimated 5-years DFS for the AYA group was 56.1% versus 86.8% for the ≥40 group, (p-value 0.71). In patients with residual disease, PFS for AYA was 34.2 (95%CI 11.5-57) months vs. 59.5 months in the ≥40 group, (p 0.009). Conclusion: Although there is no difference in pCR between the AYA age group patient treated with NACT for TNBC and the older age group, the DFS is significantly worse in the AYA than the ≥40 age group in patients with residual disease. As well, DFS is numerically worse in the AYA age vs. the ≥40 age group in patients who achieved pCR.

Citation Format: Faris Tamimi, Baha’ Sharaf, Suhaib Khater, Suhaib Al-Sawajneh, Malek Horani, Khalid M. Elrabii, Anas Zayed, Hikmat Abdel-Razeq. Neoadjuvant B27 protocol in Triple-Negative Breast Cancer: Evaluation response rate, pathological complete response rates,toxicity,and the prognosis of Adolescent and Young Adult (AYA) age group compared to older population [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-06-06.