Resistance to Targeted Inhibitors of the PI3K/AKT/mTOR Pathway in Advanced Oestrogen-Receptor-Positive Breast Cancer.

The PI3K/AKT/mTOR signalling pathway is one of the most frequently activated pathways in breast cancer and also plays a central role in the regulation of several physiologic functions. There are major efforts ongoing to exploit precision medicine by developing inhibitors that target the three kinases (PI3K, AKT, and mTOR). Although multiple compounds have been developed, at present, there are just three inhibitors approved to target this pathway in patients with advanced ER-positive, HER2-negative breast cancer: everolimus (mTOR inhibitor), alpelisib (PIK3CA inhibitor), and capivasertib (AKT inhibitor). Like most targeted cancer drugs, resistance poses a major problem in the clinical setting and is a factor that has frequently limited the overall efficacy of these agents. Drug resistance can be categorised into intrinsic or acquired resistance depending on the timeframe it has developed within. Whereas intrinsic resistance exists prior to a specific treatment, acquired resistance is induced by a therapy. The majority of patients with ER-positive, HER2-negative advanced breast cancer will likely be offered an inhibitor of the PI3K/AKT/mTOR pathway at some point in their cancer journey, with the options available depending on the approval criteria in place and the cancer's mutation status. Within this large cohort of patients, it is likely that most will develop resistance at some point, which makes this an area of interest and an unmet need at present. Herein, we review the common mechanisms of resistance to agents that target the PI3K/AKT/mTOR signalling pathway, elaborate on current management approaches, and discuss ongoing clinical trials attempting to mitigate this significant issue. We highlight the need for additional studies into AKT1 inhibitor resistance in particular.

Systemic Therapies for HER2-Positive Advanced Breast Cancer.

Despite recent advances, HER2-positive advanced breast cancer (ABC) remains a largely incurable disease, with resistance to conventional anti-HER2 drugs ultimately unavoidable for all but a small minority of patients who achieve an enduring remission and possibly cure. Over the past two decades, significant advances in our understanding of the underlying molecular mechanisms of HER2-driven oncogenesis have translated into pharmaceutical advances, with the developing of increasingly sophisticated therapies directed against HER2. These include novel, more potent selective HER2 tyrosine kinase inhibitors (TKIs); new anti-HER2 antibody-drug conjugates; and dual epitope targeting antibodies, with more advanced pharmacological properties and higher affinity. With the introduction of adjuvant T-DM1 for incomplete responders to neoadjuvant therapy, fewer patients are relapsing, but for those who do relapse, disease that may be resistant to standard first- and second-line therapies requires new approaches. Furthermore, the risk of CNS relapse has not been abrogated by current (neo)adjuvant strategies; therefore, current research efforts are being directed towards this challenging site of metastatic disease. In this article, we review the currently available clinical data informing the effective management of HER2-positive breast cancer beyond standard first-line therapy with pertuzumab, trastuzumab, and taxanes, and the management of relapse in patients who have already been exposed to both these agents and T-DM1 for early breast cancer (EBC). We additionally discuss novel anti-HER2 targeted agents and combinations in clinical trials, which may be integrated into standard treatment paradigms in the future.

Neratinib in advanced HER2-positive breast cancer: experience from the royal Marsden hospital.

PURPOSE: To describe the tolerability and efficacy of neratinib as a monotherapy and in combination with capecitabine in advanced HER2-positive breast cancer in a real-world setting. METHODS: Patients who received neratinib for advanced HER2-positive at the Royal Marsden Hospital NHS Trust between August 2016 and May 2020 were identified from electronic patient records and baseline characteristics, previous treatment and response to treatment were recorded. The primary endpoint of the study was progression-free survival (PFS). Secondary endpoints included overall survival (OS) and safety. RESULTS: Seventy-two patients were eligible for the analysis. Forty-five patients received neratinib in combination with capecitabine and 27 patients received monotherapy. After a median duration of follow-up of 38.5 months, the median PFS for all patients was 5.9 months (95% confidence interval (CI) 4.9-7.4 months) and median OS was 15.0 months (95% Cl 10.4-22.2 months). Amongst the 52.7% (38/72) patients with confirmed brain metastases at baseline, median PFS was 5.7 months (95% CI 2.9-7.4 months) and median OS was 12.5 months (95% CI 7.7-21.4 months). Despite anti-diarrhoeal prophylaxis, diarrhoea was the most frequent adverse event, reported in 64% of patients which was grade 3 in 10%. There were no grade 4 or 5 toxicities. Seven patients discontinued neratinib due to toxicity. CONCLUSIONS: Neratinib monotherapy or in combination with capecitabine is a useful treatment for patients with and without brain metastases. PFS and OS were found to be similar as previous trial data. Routine anti-diarrhoeal prophylaxis allows this combination to be safely delivered to patients in a real-world setting.

Vinorelbine After Prior Treatment With Eribulin for Advanced Breast Cancer: A Single-Centre Experience Suggesting Cross-Resistance.

INTRODUCTION: The tubulin inhibitor, eribulin, improves survival for previously treated advanced breast cancer (ABC) compared to chemotherapy of physician's choice, including vinorelbine, an older anti-tubulin. Vinorelbine is commonly still used after eribulin, but potentially risks cross-resistance and its efficacy in this setting is unproven. MATERIALS AND METHODS: A retrospective analysis of all patients who received vinorelbine after prior eribulin (VAE) 2011-2015 and a parallel cohort of consecutive patients who received vinorelbine without prior eribulin (VWE) for previously treated ABC between 2005 and 2011. Patient demographics, histopathological features, treatment duration and responses were recorded. The primary endpoint was progression-free survival from date of first vinorelbine for each cohort. Secondary endpoints included radiological response rate, and overall survival (OS). RESULTS: Thirty-five VAE and 103 VWE patients were identified, all female, 71.4% and 78.6% were ER positive/HER2 negative, 8.6% and 6.8% HER2 positive, and 20.0% and 14.6% triple negative for VAE and VWE cohorts, respectively. The median number of lines of chemotherapy lines prior to vinorelbine was 4 (range 2-6) and 2 (range 0-4), respectively. Fifteen VAE patients (42.9%) received ≥1 line of chemotherapy between eribulin and vinorelbine. VAE and WWE Patients received a median of 3 cycles of vinorelbine (range 1-9 and 1-12, respectively). The median progression-free survival for VAE patients was 2.1 months and 2.0 months for VWE patients. No VAE patients were progression-free at 24 weeks, compared to 15.5% of VWE patients. Median OS from commencing vinorelbine was 4.3 months for VAE and 6.4 months for VWE patients. CONCLUSION: Vinorelbine was of limited benefit after prior eribulin in our study, suggesting cross-resistance. Even without prior eribulin, only 15% of patients experienced clinical benefit from vinorelbine monotherapy.

Heterogeneous HER2 Amplification-a New Clinical Category of HER2-Positive Breast Cancer?

HER2 amplification heterogeneity is associated with resistance to trastuzumab emtansine in the neoadjuvant setting, emphasizing the importance of assessing whether heterogeneous HER2-positive cancers require different treatment pathways.See related article by Metzger Filho et al., p. 2474.

Treating Advanced Unresectable or Metastatic HER2-Positive Breast Cancer: A Spotlight on Tucatinib.

The management of HER2 positive breast cancer has been transformed by the development of targeted therapies. Dual blockade with the monoclonal antibodies, trastuzumab and pertuzumab, added to first-line taxane chemotherapy and second-line therapy with the antibody-drug conjugate, T-DM1, are internationally agreed standards of care for advanced HER2 positive breast cancer, where available. However, until recently, options for patients for third-line therapy and beyond were of modest efficacy or limited by toxicity. In 2019, the results of trials of two exciting new agents for this space were presented. A third-generation HER2 tyrosine kinase inhibitor, tucatinib, combines the efficacy of the second-generation drug, neratinib, with a more manageable toxicity profile and has become a new standard of care after T-DM1, in combination with capecitabine and trastuzumab. The antibody-drug conjugate, trastuzumab deruxtecan, demonstrated remarkable efficacy in heavily pre-treated patients and received accelerated approval in the United States, whilst confirmatory Phase 3 trials are completed. This review will discuss the available data for the post-T-DM1 setting, focusing on tyrosine kinase inhibitors including tucatinib.

Impact of timing of adjuvant chemothapy for early breast cancer: the Royal Marsden Hospital experience.

BACKGROUND: The optimal time to deliver adjuvant chemotherapy has not been defined. METHODS: A retrospective study of consecutive patients receiving adjuvant anthracycline and/or taxane 1993-2010. Primary endpoint included 5-year disease-free survival (DFS) in patients commencing chemotherapy <31 versus ≥31 days after surgery. Secondary endpoints included 5-year overall survival (OS) and sub-group analysis by receptor status. RESULTS: We identified 2003 eligible patients: 1102 commenced chemotherapy <31 days and 901 ≥31 days after surgery. After a median follow-up of 115 months, there was no difference in 5-year DFS rate with chemotherapy <31 compared to ≥31 days after surgery in the overall population (81 versus 82% hazard ratio (HR) 1.15, 95% confidence interval (95% CI) 0.92-1.43, p = 0.230). The 5-year OS rate was similar in patients who received chemotherapy <31 or ≥31 days after surgery (90 versus 91%, (HR 1.21, 95% CI 0.89-1.64, p = 0.228). For 250 patients with triple-negative breast cancer OS was significantly worse in patients who received chemotherapy ≥31 versus <31 days (HR = 2.18, 95% CI 1.11-4.30, p = 0.02). DISCUSSION: Although adjuvant chemotherapy ≥31 days after surgery did not affect DFS or OS in the whole study population, in TN patients, chemotherapy ≥31 days after surgery significantly reduced 5-year OS; therefore, delays beyond 30 days in this sub-group should be avoided.

Triplet Therapy with Palbociclib, Taselisib, and Fulvestrant in PIK3CA-Mutant Breast Cancer and Doublet Palbociclib and Taselisib in Pathway-Mutant Solid Cancers.

Cyclin-dependent kinase 4/6 (CDK4/6) and PI3K inhibitors synergize in PIK3CA-mutant ER-positive HER2-negative breast cancer models. We conducted a phase Ib trial investigating the safety and efficacy of doublet CDK4/6 inhibitor palbociclib plus selective PI3K inhibitor taselisib in advanced solid tumors, and triplet palbociclib plus taselisib plus fulvestrant in 25 patients with PIK3CA-mutant, ER-positive HER2-negative advanced breast cancer. The triplet therapy response rate in PIK3CA-mutant, ER-positive HER2-negative cancer was 37.5% [95% confidence interval (CI), 18.8-59.4]. Durable disease control was observed in PIK3CA-mutant ER-negative breast cancer and other solid tumors with doublet therapy. Both combinations were well tolerated at pharmacodynamically active doses. In the triplet group, high baseline cyclin E1 expression associated with shorter progression-free survival (PFS; HR = 4.2; 95% CI, 1.3-13.1; P = 0.02). Early circulating tumor DNA (ctDNA) dynamics demonstrated high on-treatment ctDNA association with shorter PFS (HR = 5.2; 95% CI, 1.4-19.4; P = 0.04). Longitudinal plasma ctDNA sequencing provided genomic evolution evidence during triplet therapy. SIGNIFICANCE: The triplet of palbociclib, taselisib, and fulvestrant has promising efficacy in patients with heavily pretreated PIK3CA-mutant ER-positive HER2-negative advanced breast cancer. A subset of patients with PIK3CA-mutant triple-negative breast cancer derived clinical benefit from palbociclib and taselisib doublet, suggesting a potential nonchemotherapy targeted approach for this population.This article is highlighted in the In This Issue feature, p. 1.

Inactivating NF1 Mutations Are Enriched in Advanced Breast Cancer and Contribute to Endocrine Therapy Resistance.

PURPOSE: Advanced breast cancer (ABC) has not been subjected to the same degree of molecular scrutiny as early primary cancer. Breast cancer evolves with time and under the selective pressure of treatment, with the potential to acquire mutations with resistance to treatment and disease progression. To identify potentially targetable mutations in advanced breast cancer, we performed prospective molecular characterization of a cohort of patients with ABC. EXPERIMENTAL DESIGN: Biopsies from patients with advanced breast cancer were sequenced with a 41 genes targeted panel in the ABC Biopsy (ABC-Bio) study. Blood samples were collected at disease progression for circulating tumor DNA (ctDNA) analysis, along with matched primary tumor to assess for acquisition in ABC in a subset of patients. RESULTS: We sequenced 210 ABC samples, demonstrating enrichment compared with primary disease for potentially targetable mutations in HER2 (in 6.19% of samples), AKT1 (7.14%), and NF1 (8.10%). Of these enriched mutations, we show that NF1 mutations were frequently acquired in ABC, not present in the original primary disease. In ER-positive cancer cell line models, loss of NF1 resulted in endocrine therapy resistance, through both ER-dependent and -independent mechanisms. NF1 loss promoted ER-independent cyclin D1 expression, which could be therapeutically targeted with CDK4/6 inhibitors in vitro. Patients with NF1 mutations detected in baseline circulating tumor DNA had a good outcome on the CDK4/6 inhibitor palbociclib and fulvestrant. CONCLUSIONS: Our research identifies multiple therapeutic opportunities for advanced breast cancer and identifies the previously underappreciated acquisition of NF1 mutations.

To Cycle or Fight-CDK4/6 Inhibitors at the Crossroads of Anticancer Immunity.

Dysregulation of cell division resulting in aberrant cell proliferation is a key hallmark of cancer, making it a rational and important target for innovative anticancer drug development. Three selective cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors are FDA and European Medicines Agency (EMA) approved for hormone receptor-positive/HER2-negative advanced breast cancer. A major emerging appreciation is that these inhibitors not only are cytostatic, but also play critical roles in the interaction between tumor cells and the host immune response. However, to trigger an effective immune response, lymphocytes must also proliferate. This review aims to assimilate our emerging understanding on the role of CDK4/6 inhibitors in cell-cycle control, as well as their biological effect on T cells and other key immune cells, and the confluence of preclinical evidence of augmentation of anticancer immunity by these drugs. We aim to provide a framework for understanding the role of the cell cycle in anticancer immunity, discussing ongoing clinical trials evaluating this concept and challenges for developing rational combinations with immunotherapy.

Effect of Pathologic Tumor Response and Nodal Status on Survival in the Medical Research Council Adjuvant Gastric Infusional Chemotherapy Trial.

PURPOSE: The Medical Research Council Adjuvant Gastric Infusional Chemotherapy (MAGIC) trial established perioperative epirubicin, cisplatin, and fluorouracil chemotherapy as a standard of care for patients with resectable esophagogastric cancer. However, identification of patients at risk for relapse remains challenging. We evaluated whether pathologic response and lymph node status after neoadjuvant chemotherapy are prognostic in patients treated in the MAGIC trial. MATERIALS AND METHODS: Pathologic regression was assessed in resection specimens by two independent pathologists using the Mandard tumor regression grading system (TRG). Differences in overall survival (OS) according to TRG were assessed using the Kaplan-Meier method and compared using the log-rank test. Univariate and multivariate analyses using the Cox proportional hazards method established the relationships among TRG, clinical-pathologic variables, and OS. RESULTS: Three hundred thirty resection specimens were analyzed. In chemotherapy-treated patients with a TRG of 1 or 2, median OS was not reached, whereas for patients with a TRG of 3, 4, or 5, median OS was 20.47 months. On univariate analysis, high TRG and lymph node metastases were negatively related to survival (Mandard TRG 3, 4, or 5: hazard ratio [HR], 1.94; 95% CI, 1.11 to 3.39; P = .0209; lymph node metastases: HR, 3.63; 95% CI, 1.88 to 7.0; P < .001). On multivariate analysis, only lymph node status was independently predictive of OS (HR, 3.36; 95% CI, 1.70 to 6.63; P < .001). CONCLUSION: Lymph node metastases and not pathologic response to chemotherapy was the only independent predictor of survival after chemotherapy plus resection in the MAGIC trial. Prospective evaluation of whether omitting postoperative chemotherapy and/or switching to a noncross-resistant regimen in patients with lymph node-positive disease whose tumor did not respond to preoperative epirubicin, cisplatin, and fluorouracil may be appropriate.

Current and Future Therapies for Advanced Gastric Cancer.

The treatment of patients with advanced gastric cancer remains a challenging area of oncology. Extensive trials of differing chemotherapy regimens have yielded no international consensus on the optimal combination, and overall survival with chemotherapy alone remains poor. Recently an improved understanding of the molecular drivers of the disease has opened up promising new avenues of treatment through the use of biological targeted agents. The anti-HER2 monoclonal antibody trastuzumab was the first targeted agent to significantly prolong survival in the first-line treatment of a molecularly-selected subgroup of patients. More recently the anti-vascular endothelial growth factor receptor 2 monoclonal antibody ramucirumab has demonstrated a modest survival benefit in previously treated patients as both a monotherapy and in combination with chemotherapy. Immunotherapy and the use of checkpoint inhibitors are a further exciting area of development with promising preliminary results for the activity of the anti-Programmed Death 1 Receptor antibody pembrolizumab and ongoing trials of a number of immune-modulating agents. Continuing research to identify novel targets and therapies aims to make further incremental gains in survival. In this review we outline the evidence base supporting current chemotherapy regimens and describe the latest advances in the development and use of molecularly targeted and immune-modulating agents.

Trastuzumab: a novel standard option for patients with HER-2-positive advanced gastric or gastro-oesophageal junction cancer.

The human epidermal receptor-2 (HER-2) is amplified in up to 25% of patients with gastroesophageal adenocarcinomas. Although the presence of this amplification does not appear to confer a poor prognosis, it provides a valuable novel therapeutic target for this group of patients. Trastuzumab is a fully humanized monoclonal antibody directed at HER-2 which binds the external domain of the receptor and exerts its action via a combination of antibody-dependent cytotoxicity, reduced shedding of the extracellular domain, inhibition of dimerization and possibly receptor downregulation. The ToGA trial was an international multicentre randomized phase III study which evaluated the addition of trastuzumab to a cisplatin plus fluoropyrimidine chemotherapy doublet in 594 patients with HER-2-positive advanced gastric or oesophagogastric junction adenocarcinoma. The combination of the antibody with chemotherapy significantly improved response rate, median progression-free survival and median overall survival without additional toxicity or adversely affecting quality of life. Accordingly, trastuzumab plus chemotherapy is now a standard first-line treatment option for patients with advanced HER-2-positive gastroesophageal cancer. Unfortunately, many patients with HER-2-positive cancer exhibit primary resistance to trastuzumab and the remainder will acquire resistance to the antibody; therefore, urgent investigation into novel agents which may circumvent resistance mechanisms is warranted. Small molecule inhibitors of HER-2, which commonly also target other members of the HER family of receptors, such as EGFR and HER-3, are currently undergoing evaluation in gastroesophageal cancer as first-line alternatives to trastuzumab and second-line salvage treatments for trastuzumab-resistant disease. Extrapolating the successful use of trastuzumab in the advanced disease setting, clinical trials are underway to assess the role of this antibody in the perioperative and adjuvant settings, where it is hoped that it will have a meaningful impact upon the currently poor survival rates.

Targeting angiogenesis in esophagogastric adenocarcinoma.

The possibility of targeting tumor angiogenesis was postulated almost 40 years ago. The vascular endothelial growth factor (VEGF) family and its receptors have since been characterized and extensively studied. VEGF overexpression is a common finding in solid tumors, including esophagogastric cancer, and frequently correlates with poor prognosis. Monoclonal antibodies, soluble receptors, and small-molecule tyrosine kinase inhibitors have been developed to inhibit tumor angiogenesis, and antiangiogenic therapy is now a component of standard treatment for advanced renal cell, hepatocellular, colorectal, breast, and non-small cell lung carcinomas. The small-molecule tyrosine kinase inhibitors sunitinib and sorafenib have been evaluated in phase II studies in esophagogastric cancer but appear to have only modest activity. Similarly, despite promising efficacy signals from phase II studies, the addition of the anti-VEGF-A monoclonal antibody bevacizumab to cisplatin plus capecitabine failed to result in a longer overall survival duration than with the chemotherapy doublet plus placebo. The response rate and progression-free survival interval were significantly greater with bevacizumab, confirming some efficacy in advanced gastric cancer, but with inadequate benefit to justify the high cost of treatment. Evaluation of bevacizumab in the neoadjuvant and perioperative settings continues, hypothesizing that a higher response rate will translate into longer survival in patients with operable disease. Despite extensive research, the discovery of a reliable predictive biomarker for antiangiogenic therapy continues to elude the scientific and oncology communities, and mechanisms of primary and acquired resistance are incompletely understood. We are therefore currently unable to personalize antiangiogenic therapy for established indications, or use molecular selection for clinical trials evaluating novel indications.

Optimal therapeutic strategies for resectable oesophageal or oesophagogastric junction cancer.

Oesophageal cancer is the eighth most common cancer diagnosed worldwide, with almost half a million new cases diagnosed each year. Despite improvements in surgical and radiotherapy techniques and refinements of chemotherapeutic regimens, long-term survival, even from localized oesophageal cancer, remains poor. Surgical resection alone remains the standard approach for very early stage disease (stage I), but whilst surgery remains fundamental to the treatment of stage II-III resectable adenocarcinoma, multimodality therapy with chemotherapy or chemoradiation (CRT) is internationally accepted as the standard of care. Data from two large, randomized phase III trials support the use of perioperative combination chemotherapy in lower oesophageal and oesophagogastric junction adenocarcinomas, but the contribution of the adjuvant therapy is uncertain. There are conflicting data from randomized studies of a purely neoadjuvant approach; however, recent meta-analyses have demonstrated that chemotherapy or CRT given prior to radical surgery improves survival in patients with adenocarcinoma of the oesophagus. Neoadjuvant CRT but not chemotherapy alone is also beneficial for patients with squamous cell carcinoma. Definitive CRT has emerged as a useful option for the treatment of resectable squamous cell carcinoma of the oesophagus, avoiding potential surgical morbidity and mortality for most patients, with salvage surgery reserved for those with persistent disease. In this review, we focus on the pharmacotherapy of resectable oesophageal and oesophagogastric junction cancers and how clinical trials and meta-analyses inform current clinical practice.

Docetaxel and irinotecan as second-line therapy for advanced oesophagogastric cancer.

INTRODUCTION: Systemic chemotherapy improves survival in oesophagogastric cancer however no standard second-line regimen exists due to a paucity of randomised data. Docetaxel combined with irinotecan (DI) provides a suitable option due to the lack of cross-reactivity with first-line therapeutics and a tolerable toxicity profile. METHODS: We retrospectively reviewed a cohort of patients with advanced oesophagogastric cancer in two institutions treated with the combination of docetaxel 35 mg/m(2) plus irinotecan 60 mg/m(2) day 1 and day 8 every 21 days, following progression with first-line platinum-based therapy. RESULTS: Between January 2000 and September 2009, 41 eligible patients were identified. Median age was 58 years, male:female 25:16, adenocarcinoma:squamous cell carcinoma 37:4, oesophageal:oesophagogastric junction:gastric 7:10:24. Locally advanced:metastatic disease 6:35. Previous radical surgery:radiotherapy:both 6:4:7. 27/41 had progressed within 90 days of receiving platinum-based therapy. Median number of chemotherapy cycles: 3 (range 1-12). Eight patients required dose reductions due to DI toxicity. 10/28 evaluable patients had a response, median progression-free survival (PFS) was 11 weeks (95% confidence intervals (CI): 9-13 weeks) with median overall survival 24 weeks (95%CI: 12-35 weeks). No significant prognostic factors were identified. CONCLUSION: Weekly docetaxel combined with irinotecan has acceptable safety and modest efficacy in the second-line treatment of advanced oesophagogastric cancer. Further prospective evaluation of this regimen is warranted.

Metastatic breast cancer presenting as a primary hindgut neuroendocrine tumour.

The examination of limited, potentially non-representative fragments of tumour tissue from a core biopsy can be misleading and misdirect subsequent treatment, especially in cases where a primary tumour has not been identified. This case report is of a 65-year-old woman presenting with a destructive sacral mass, diagnosed on radiological imaging and core biopsy as a hindgut neuroendocrine tumour, which on histopathological review of the subsequently resected tumour was found instead to represent a metastasis from an occult hormone-positive breast cancer with neuroendocrine features.