Proficiency testing of PIK3CA mutations in HR+/HER2-breast cancer on liquid biopsy and tissue

The role of PIK3CA mutation in lobular breast cancer in the era of precision oncology - a systematic review

BACKGROUND

Ιnvasive lobular carcinoma (ILC) is a distinct subtype of breast cancer with unique clinical and molecular features. Although ILC generally responds to endocrine therapy, it tends to exhibit lower chemotherapy sensitivity, underscoring the need for tailored therapeutic approaches. PIK3CA mutations are frequently observed in ILC. This systematic review evaluates the prevalence of PIK3CA mutations in ILC and examines their prognostic and predictive significance.

METHODS

We searched PubMed and Scopus for studies reporting PIK3CA mutations in lobular breast cancer. Inclusion criteria encompassed studies on stage I-III ILC examining mutation frequency, prognosis, or predictive value. Data on mutation prevalence in ILC (and comparisons to invasive ductal carcinoma, IDC) and associated outcomes were extracted. Meta-analyses were performed with assessment of heterogeneity and publication bias.

RESULTS

Ten relevant studies (nine cohorts) were included. The prevalence of PIK3CA mutations in ILC ranged from ~30% to ~50%. Statistic analysis showed that nearly half of ILCs harbor PIK3CA mutations. Mutation rates in ILC were generally higher than in IDC. No significant association between PIK3CA mutation status and patient prognosis was observed in the available studies. There were limited data ontreatment response.

CONCLUSIONS

PIK3CA is a commonly mutated gene in ILC, but current evidence does not demonstrate a clear impact on prognosis or definite predictive value for therapy response in this subtype. Nonetheless, the high mutation frequency provides a rationale for targeted therapeutic approaches. PIK3CA testing may be considered in advanced ILC to identify candidates for PI3K inhibitor therapy, although further research is needed.

Beyond traditional biopsies: the emerging role of ctDNA and MRD on breast cancer diagnosis and treatment

Breast cancer management has traditionally relied on tissue biopsies and imaging, which offer limited insights into the disease. However, the discovery of circulating tumor DNA (ctDNA) and minimal residual disease (MRD) detection has revolutionized our approach to breast cancer. ctDNA, which is fragmented tumor DNA found in the bloodstream, provides a minimally invasive way to understand the tumor's genomic landscape, revealing heterogeneity and critical mutations that biopsies may miss. MRD, which indicates cancer cells that remain after treatment, can now be detected using ctDNA and other advanced methods, improving our ability to predict disease recurrence. This allows for personalized adjuvant therapies based on individual MRD levels, avoiding unnecessary treatments for patients with low MRD. This review discusses how ctDNA and MRD represent a paradigm shift towards personalized, genomically guided cancer care, which has the potential to significantly improve patient outcomes in breast cancer.

PI3K/AKT/mTOR inhibitors for hormone receptor-positive advanced breast cancer

Dysregulation of the phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) pathway plays a pivotal role in the development and progression of various cancers. In hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer, aberrations in this pathway are increasingly recognized as key drivers of resistance to endocrine therapy and cyclin-dependent kinase 4/6 (CDK4/6) inhibitors, the first-line treatments for this disease subtype. Recognizing the urgent need for alternative therapeutic strategies, significant advancements have been made in developing PI3K/AKT/mTOR inhibitors for HR+ advanced/metastatic breast cancer. Among these inhibitors, capivasertib and alpelisib have received approval as targeted therapies for this indication. This review provides a comprehensive summary of the latest developments in PI3K/AKT/mTOR inhibitors for HR+ breast cancer. It also delves into different aspects, including sampling, testing method and timing, of PI3K/AKT/mTOR diagnostic testing. Additionally, the review discusses key considerations for integrating these inhibitors into clinical practice, such as timing and choice of PI3K/AKT/mTOR inhibitors, and management of treatment toxicities. By examining these different aspects, this review aims to provide valuable insights into optimizing the clinical utility of PI3K/AKT/mTOR inhibitors in HR+ advanced breast cancer.

Circulating tumor DNA fraction predicts residual cancer burden post-neoadjuvant chemotherapy in triple negative breast cancer

Purpose

Pathologic response after preoperative/neoadjuvant chemotherapy (NAC) is a continuum that can range from complete pathologic response (pCR) to extensive residual disease (RD). We hypothesized that post-NAC plasma circulating tumor DNA (ctDNA) fraction (TF) reflect pathologic response as continuum measured by the residual cancer burden (RCB) score.

Methods

ctDNA was assessed using the PredicineBEACON assay, that interrogates up to 50 personalized tumor variants and 500 hot-spot mutations, in 3 mL archived plasma isolated from EDTA tubes collected post-NAC but before surgery from 44 patients with stage I/III triple negative breast cancer (TNBC) who received durvalumab and weekly nab-paclitaxel followed by doxorubicin/cyclophosphamide on a clinical trial (NCT02489448). Circulating free tumor DNA methylation profiling was performed using PredicineEPIC assay in paired pre- and post-NAC plasma (N = 30). Youden's J-statistics was used to define optimal thresholds.

Results

We observed a significant positive correlation (r = 0.45, p = 0.004) between RCB scores and post-NAC TF. The median TF was significantly lower in pCR (RCB0) compared to RD patients (0.06 % vs. 0.3 %, p = 0.02). Using a TF positivity threshold of ≥0.05 %, PredicineBEACON had 58 % sensitivity at 83 % specificity for identifying RD. TF was higher in patients who experienced recurrence (n = 9) compared to those without recurrence (n = 35) (0.17 % vs. 0.05 % TF, p = 0.029). There was significant decrease in methylation signal in post-compared to pre-NAC samples, but post-treatment methylation signal was lower in cases with pCR vs RD.

Conclusions

Post-NAC plasma tumor fraction and change in tumor-derived methylation signal predict the extent of RD and recurrence in TNBC patients.

PIK3CA mutational status in tissue and plasma as a prognostic biomarker in HR+/HER2- breast cancer

INTRODUCTION

Hotspots (HS) mutations in the PIK3CA gene may lead to poorer oncological outcomes and endocrine resistance in advanced breast cancer (BC), but their prognostic role in early-stage disease remains controversial. The overall agreement within plasma and tissue methods has not been well explored. Our aim was to correlate tissue and plasma approaches and to analyze the prognostic impact of PIK3CA mutations (PIK3CAm) in HR+/HER2- BC.

METHODS

A retrospective and unicentric analysis of PIK3CA mutational status in tissue and plasma samples by Cobas®PIK3CA Mutation Kit in patients with HR+/HER2- BC.

RESULTS

We analyzed 225 samples from 161 patients with luminal BC. PIK3CA mutations were identified in 62 patients (38.5%), of which 39.6% were found in tissue and 11.8% in plasma. In advanced disease, plasma and tissue correlation rate was performed in 64 cases, with an overall agreement of 70.3%. Eighty patients were treated with CDK4/6 inhibitors + endocrine therapy. We observed a moderately worse progression-free survival (PFS) in PIK3CAm versus wild-type (WT) (24 m vs. 30 m; HR = 1.39, p = 0.26). A subanalysis was carried out based on exons 9 and 20, which showed a statistically poorer PFS in PIK3CAm exon 9 versus 20 population (9.7 m vs. 30.3 m; HR = 2.84; p = 0.024). Furthermore, detection of PIK3CAm in plasma was linked to a worse PFS vs PIK3CAm detection just in tissue (12.4 vs. 29.3; HR = 2.4; p = 0.08).

CONCLUSIONS

Our findings suggest the PIK3CA evaluation in tissue as the diagnostic method of choice, however, additional investigations are required to improve the role of liquid biopsy in the PIK3CA assessment. PIK3CAm show worse outcomes in advanced luminal BC, especially in exon 9 mutation carriers, despite visceral involvement, prior exposure to endocrine therapy or detection of PIK3CAm in plasma, with an unclear prognosis in early-stage disease. Nonetheless, this should be validated in a prospective cohort study.

Quality-Assured Analysis of PIK3CA Mutations in Hormone Receptor-Positive/Human Epidermal Growth Factor Receptor 2-Negative Breast Cancer Tissue

In precision oncology, reliable testing of predictive molecular biomarkers is a prerequisite for optimal patient treatment. Interlaboratory comparisons are a crucial tool to verify diagnostic performance and reproducibility of one's approach. Herein is described the design and results of the first recurrent, internationally performed PIK3CA (phosphatidylinositol-4,5-bisphosphate 3 kinase catalytic subunit α) breast cancer tissue external quality assessment (EQA), organized by German Quality in Pathology GmbH and started in 2021. After the internal pretesting phase performed by the (lead) panel institutes, in both 2021 and 2022, each EQA test set comprised n = 10 tissue samples of hormone receptor-positive, human epidermal growth factor receptor 2-negative invasive breast cancer that had to be analyzed and reported by the participants. In 2021, the results were evaluated separately for German-speaking countries (part 1) and international laboratories (part 2). In 2022, the EQA was performed across the European Union. The EQA success rates were 84.6% (n = 11/13), 88.6% (n = 39/44), and 87.9% (n = 29/33) for EQA 2021 part 1, part 2, and EQA 2022, respectively. The most commonly used methods were next-generation sequencing and mutation-/allele-specific qualitative PCR-based assays. In summary, this recurrent PIK3CA EQA proved to be a suitable approach to obtain an international overview of methods used for PIK3CA mutation analysis, to evaluate them qualitatively, and identify the strengths and weaknesses of individual methods.

PIK3CA testing in hormone receptor-positive/HER2-negative metastatic breast cancer: real-world data from Italian molecular pathology laboratories

Introduction: PIK3CA gene mutations occur in approximately 40% of hormone receptor-positive/HER2-negative (HR+/HER2-) metastatic breast cancers (MBCs), electing them to targeted therapy. Testing PIK3CA status is complex due to selection of biological specimen and testing method. Materials & methods: This work investigates real-life experience on PIK3CA testing in HR+/HER2- MBC. Clinical, technical and molecular data on PIK3CA testing were collected from two referral laboratories. Additionally, the results of a nationwide PIK3CA survey involving 116 institutions were assessed. Results: Overall, n = 35 MBCs were PIK3CA-mutated, with mutations mostly occurring in exons 9 (n = 19; 51.4%) and 20 (n = 15; 40.5%). The nationwide survey revealed significant variability across laboratories in terms of sampling methodology, technical assessment and clinical report signing healthcare figures for PIK3CA molecular testing in diagnostic routine practice. Conclusion: This study provides insights into the real-world routine of PIK3CA testing in HR+/HER2- MBC and highlights the need for standardization and networking in predictive pathology.

Pre-analytical conditions and implementation of quality control steps in liquid biopsy analysis

Over the last decade, great advancements have been made in the field of liquid biopsy through extensive research and the development of new technologies that facilitate the use of liquid biopsy for cancer patients. This is shown by the numerous liquid biopsy tests that gained clearance by the US Food and Drug Administration (FDA) in recent years. Liquid biopsy has significantly altered cancer treatment by providing clinicians with powerful and immediate information about therapeutic decisions. However, the clinical integration of liquid biopsy is still challenging and there are many critical factors to consider prior to its implementation into routine clinical practice. Lack of standardization due to technical challenges and the definition of the clinical utility of specific assays further complicates the establishment of Standard Operating Procedures (SOPs) in liquid biopsy. Harmonization of laboratories to established guidelines is of major importance to overcome inter-lab variabilities observed. Quality control assessment in diagnostic laboratories that offer liquid biopsy testing will ensure that clinicians can base their therapeutic decisions on robust results. The regular participation of laboratories in external quality assessment schemes for liquid biopsy testing aims to promptly pinpoint deficiencies and efficiently educate laboratories to improve their quality of services. Accreditation of liquid biopsy diagnostic laboratories based on the ISO15189 standard in Europe or by CLIA/CAP accreditation procedures in the US is the best way to achieve the adaptation of liquid biopsy into the clinical setting by assuring reliable results for the clinicians and their cancer patients. Nowadays, various organizations from academia, industry, and regulatory agencies collaborate to set a framework that will include all procedures from the pre-analytical phase and the analytical process to the final interpretation of results. In this review, we underline several challenges in the analysis of circulating tumor DNA (ctDNA) and circulating tumor cells (CTCs) concerning standardization of protocols, quality control assessment, harmonization of laboratories, and compliance to specific guidelines that need to be thoroughly considered before liquid biopsy enters the clinic.