Novel Treatment Strategies for Hormone Receptor (HR)-Positive, HER2-Negative Metastatic Breast Cancer

Estrogen receptor (ER)-positive breast cancer (BC) is the most common BC subtype. Endocrine therapy (ET) targeting ER signaling still remains the mainstay treatment option for hormone receptor (HR)-positive BC either in the early or in advanced setting, including different strategies, such as the suppression of estrogen production or directly blocking the ER pathway through SERMs-selective estrogen receptor modulators-or SERDs-selective estrogen receptor degraders. Nevertheless, the development of de novo or acquired endocrine resistance still remains challenging for oncologists. The use of novel ET combined with targeted drugs, such as cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors, has significantly improved long-term outcome rates, thus changing the therapeutic algorithm for metastatic BC (MBC) and recently the therapeutic strategy in the adjuvant setting for early high-risk BC. Eluding the resistance to CDK4/6 inhibitors combined with ET is currently an unmet medical need, and there is disagreement concerning the best course of action for patients who continue to progress after this combination approach. Genetic changes in the tumor along its growth uncovered by genomic profiling of recurrent and/or metastatic lesions through tumor and/or liquid biopsies may predict the response or resistance to specific agents, suggesting the best therapeutic strategy for each patient by targeting the altered ER-dependent pathway (novel oral SERDs and a new generation of anti-estrogen agents) or alternative ER-independent signaling pathways such as PI3K/AKT/mTOR or tyrosine kinase receptors (HER2 mutations or HER2 low status) or by inhibiting pathways weakened through germline BRCA1/2 mutations. These agents are being investigated as single molecules and in combination with other target therapies, offering promising weapons to overcome or avoid treatment failure and propose increasingly more personalized treatment approaches. This review presents novel insights into ET and other targeted therapies for managing metastatic HR+/HER2- BC by exploring potential strategies based on clinical evidence and genomic profiling following the failure of the CDK4/6i and ET combination.

Progression after First-Line Cyclin-Dependent Kinase 4/6 Inhibitor Treatment: Analysis of Molecular Mechanisms and Clinical Data

Cyclin-dependent kinase 4/6 inhibitors (CDK4/6iss) are widely used in first-line metastatic breast cancer. For patients with progression under CDK4/6is, there is currently no standard treatment recommended at the category 1 level in international guidelines. The purpose of this article is to review the cellular mechanisms underlying the resistance to CDK4/6is, as well as treatment strategies and the clinical data about the efficacy of subsequent treatments after CDK4/6is-based therapy. In the first part, this review mainly discusses cell-cycle-specific and cell-cycle-non-specific resistance to CDK4/6is, with a focus on early and late progression. In the second part, this review analyzes potential therapeutic approaches and the available clinical data on them: switching to other CDK4/6is, to another single hormonal therapy, to other target therapies (PI3K, mTOR and AKT) and to chemotherapy.

Treatment patterns and outcomes associated with sequential and non-sequential use of CDK4 & 6 inhibitors in patients with HR+, HER2- MBC in the real world

PURPOSE

Cyclin Dependent Kinase 4 & 6 inhibitors (CDK4 & 6i) have transformed the management of HR+, HER2- metastatic breast cancer (MBC); however, the optimal sequence of these treatments and other systemic therapies for MBC remains unclear.

METHODS

This study analyzed electronic medical records from the ConcertAI Oncology Dataset. US patients who received abemaciclib and at least one other systemic line of therapy (LOT) for HR+, HER2- MBC were eligible. Treatment sequences were grouped, and data for two pairs of groups are presented herein (N = 397): Group 1 (1L CDK4 & 6i to 2L CDK4 & 6i) vs. Group 2 (1L CDK4 & 6i to 2L non-CDK4 & 6i), and Group 3 (2L CDK4 & 6i to 3L CDK4 & 6i) vs. Group 4 (2L CDK4 & 6i to 3L non-CDK4 & 6i). Time-to-event outcomes (PFS and PFS-2) were analyzed using Kaplan-Meier method and Cox proportional hazard regression.

RESULTS

In the total cohort of 690 patients, the most prevalent sequence was 1L CDK4 & 6i to 2L CDK4 & 6i (n = 165). For the 397 patients across Groups 1-4, sequential CDK4 & 6i demonstrated numerically longer PFS and PFS-2 versus non-sequential CDK4 & 6i. Adjusted results demonstrate that patients in Group 1 demonstrated significantly longer PFS (p = 0.05) versus Group 2.

CONCLUSIONS

Although retrospective and hypothesis-generating, these data demonstrate numerically longer outcomes in the subsequent LOT associated with sequential CDK4 & 6i treatment.

Filling the Gap after CDK4/6 Inhibitors: Novel Endocrine and Biologic Treatment Options for Metastatic Hormone Receptor Positive Breast Cancer

The rise of cyclin-dependent kinase (CDK)4/6 inhibitors has rapidly reshaped treatment algorithms for hormone receptor (HR)-positive metastatic breast cancer, with endocrine treatment (ET) plus a CDK4/6-inhibitor currently representing the standard of care in the first line setting. However, treatment selection for those patients experiencing progression while on ET + CDK4/6-inhibitors remains challenging due to the suboptimal activity or significant toxicities of the currently available options. There is also a paucity of data regarding the efficacy of older regimens, such as everolimus + exemestane, post-CDK4/6 inhibition. In this setting of high unmet need, several clinical trials of novel drugs have recently reported encouraging results: the addition of the AKT-inhibitor capivasertib to fulvestrant demonstrated a significant improvement in progression-free survival (PFS); the oral selective estrogen receptor degrader (SERD) elacestrant prolonged PFS compared to traditional ET in a phase 3 trial, particularly among patients with detectable ESR1 mutations; finally, PARP inhibitors are available treatment options for patients with pathogenic BRCA1/2 germline mutations. Overall, a plethora of novel endocrine and biologic treatment options are finally filling the gap between first-line ET and later line chemotherapy. In this review article, we recapitulate the activity of these novel treatment options and their potential role in future treatment algorithms.

Real-World Patient Characteristics, Utilization Patterns, and Outcomes of US Patients with HR+, HER2- Metastatic Breast Cancer Treated with Abemaciclib

BACKGROUND

Abemaciclib is the most recent oral cyclin-dependent kinase 4 and 6 inhibitor (CDK4 & 6i) to receive US Food and Drug Administration (FDA) approval to treat hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) advanced or metastatic breast cancer (MBC). Administrative claims data were used to describe patient characteristics and select clinical and economic outcomes in US patients treated in routine clinical practice. Prior analyses from electronic health records data indicate approximately 25% of patients received either palbociclib or ribociclib for MBC before initiating abemaciclib treatment; this work further explored these findings and associated outcomes.

METHODS

This retrospective study analyzed medical and pharmacy claims from the IBM^® MarketScan^® Research Databases between 1 January 2007 to 31 January 2020. Patients with HR+, HER2- MBC newly initiating abemaciclib between 1 September 2017 and 31 October 2019 were included and grouped by concomitant therapy (+aromatase inhibitor (AI), +fulvestrant (F), 200 mg abemaciclib monotherapy (Mono), or +other), and outcomes were analyzed by prior CDK4 & 6i use. Patient and treatment characteristics were summarized with descriptive statistics. Kaplan-Meier methods assessed time-to-discontinuation (TTD; i.e., persistency) and time-to-chemotherapy (TTC). Adherence (defined by the medication possession ratio) and drug wastage were determined.

RESULTS

This analysis included 454 patients (mean age 57.7 years), with 35.0% (n = 159) in the +F group, 29.3% (n = 133) in the +AI group, 10.4% (n = 47) in the 200 mg Mono group, and 25.3% (n = 115) in the +other group. Prior chemotherapy and CDK 4 & 6i use were present in 23.8% and 49.8% of all patients, respectively. Visceral metastases were present at abemaciclib initiation in 50.4% in the +AI group; 49.7% in the +F group; and 55.3% in the 200 mg Mono group. Liver metastases were present in 33.7% of the overall population. Among patients without prior CDK4 & 6i use, the median TTD for patients receiving abemaciclib + AI was not reached [95% CI 430-not reached (NR) days], abemaciclib + F [531 days (95% CI 281-NR)], and abemaciclib mono [141 days (95% CI 80-NR)]. Median TTC for abemaciclib + AI and abemaciclib + F groups were not reached and the median TTC for abemaciclib mono was 535 days (95% CI 181-NR). Medication adherence was 88.7% and medication wastage costs among those with at least one dose modification were $808.12 and $452.2 per patient per month based on amount paid and wholesale acquisition cost (WAC), respectively. Mean length of follow-up for all patients was 350 days (SD 187).

CONCLUSION

These real-world data complement clinical trial results by examining abemaciclib use among patients treated in routine clinical practice. The sizeable number of patients treated with prior CDK4 & 6i, chemotherapy, and/or visceral metastases at abemaciclib initiation suggest that many patients had very advanced disease and/or were in later stages of their treatment. These data confirm a higher percentage of patients treated with previous CDK4 & 6i than reported previously, reinforcing the importance of the ongoing, prospective clinical trials evaluating outcomes following progression on CDK4 & 6i.

Treatment of Luminal Metastatic Breast Cancer beyond CDK4/6 Inhibition: Is There a Standard of Care in Clinical Practice?

BACKGROUND

CDK4/6 inhibitors have become the standard for first-line treatment of metastatic luminal breast cancer based on consistent data from several phase 3 trials demonstrating clinically meaningful improvement of progression-free as well as overall survival. In addition, they are about to become a part of adjuvant treatment for patients with high-risk luminal disease based on positive results from the first randomized phase 3 trial on abemaciclib. Nevertheless, the majority of patients with advanced or metastatic luminal breast cancer and prospectively a relevant proportion of patients treated in the adjuvant setting will eventually develop resistance to this endocrine based combination within 12-36 months, depending on the line of treatment.

CONCLUSION

Potential subsequent therapies include PI3K inhibitors, mTOR inhibitors, endocrine monotherapy, PARP inhibitors, and chemotherapy. However, these therapies have mainly been developed in the pre-CDK4/6 inhibitor era and little is known about potential cross-resistance. The concept of continuing CDK4/6 inhibition beyond progression is supported by some preclinical data, but to date there is very limited clinical evidence to support this strategy. Therefore, treatment of metastatic luminal breast cancer after progression on CDK4/6 inhibitors remains a challenge.

KEY MESSAGES

Here we review current evidence from pro- and retrospective studies and give an outlook on future developments with respect to novel therapeutic agents, including oral SERD and AKT inhibitors, which have the potential to change the therapeutic landscape in the future. Furthermore, clinical treatment algorithms and current research will also be discussed.

Response to Abemaciclib After 10 Lines of Therapy Including Palbociclib in Metastatic Breast Cancer: A Case Report With Literature Review

Metastatic breast cancer (BC) is considered incurable, and it is generally treated with sequential single-agent therapies to control it with palliative intent. Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) are used in the front-line setting of hormone receptor (HR)-positive, HER2-negative BC, and guidelines discourage the use of a second-line CDK4/6i after failure of first-line use of this class of drugs due to lack of data supporting this practice. We report a case of a postmenopausal woman with HR-positive and HER2-negative advanced BC who was treated with four lines of hormonal therapy and more than five chemotherapy regimens, with progression. Palbociclib was used in the sixth-line therapy and discontinued after 5 months. We then tried abemaciclib in the 11th-line setting, where it induced a response that lasted 16 months.

The genomics of undifferentiated sarcoma of soft tissue: Progress, challenges and opportunities

Undifferentiated sarcoma of soft tissue (USTS) are aggressive sarcomas that remain a diagnosis of exclusion and show extreme genomic complexity. Many advances in diagnostic criteria have resulted in several revisions in the definition of this rare cancer type. Recent sequencing efforts have illuminated the nature of the genome complexity and have revealed extensive copy number heterogeneity and multiple evolutionary patterns of development. This review places these recent advances into their historical and translational context and covers the changes in nomenclature, molecular classification, and the promise of personalised medicine.