APOBEC3 mutagenesis drives therapy resistance in breast cancer.

Acquired genetic alterations commonly drive resistance to endocrine and targeted therapies in metastatic breast cancer 1-7 , however the underlying processes engendering these diverse alterations are largely uncharacterized. To identify the mutational processes operant in breast cancer and their impact on clinical outcomes, we utilized a well-annotated cohort of 3,880 patient samples with paired tumor-normal sequencing data. The mutational signatures associated with apolipoprotein B mRNA-editing enzyme catalytic polypeptide-like 3 (APOBEC3) enzymes were highly prevalent and enriched in post-treatment compared to treatment-naïve hormone receptor-positive (HR+) cancers. APOBEC3 mutational signatures were independently associated with shorter progression-free survival on antiestrogen plus CDK4/6 inhibitor combination therapy in patients with HR+ metastatic breast cancer. Whole genome sequencing (WGS) of breast cancer models and selected paired primary-metastatic samples demonstrated that active APOBEC3 mutagenesis promoted resistance to both endocrine and targeted therapies through characteristic alterations such as RB1 loss-of-function mutations. Evidence of APOBEC3 activity in pre-treatment samples illustrated a pervasive role for this mutational process in breast cancer evolution. The study reveals APOBEC3 mutagenesis to be a frequent mediator of therapy resistance in breast cancer and highlights its potential as a biomarker and target for overcoming resistance.

Predictors of Response to CDK4/6i Retrial After Prior CDK4/6i Failure in ER+ Metastatic Breast Cancer.

After disease progression on endocrine therapy (ET) plus a CDK4/6 inhibitor, there is no standardized sequence for subsequent treatment lines for estrogen receptor positive (ER+) metastatic breast cancer (MBC). CDK4/6i retrial as a treatment strategy is commonplace in modern clinical practice; however, the available prospective data investigating this strategy have had inconclusive results. To frame this data in a real-world context, we performed a retrospective analysis assessing the efficacy of CDK4/6is in 195 patients who had previous exposure to CDK4/6i in a prior treatment line at our institution. Among patients who had stopped a CDK4/6i due to toxicity, CDK4/6i retrial either immediately after with a different CDK4/6i or in a further treatment line with the same initial CDK4/6i was both safe and effective, with a median time to treatment failure (TTF) of 10.1 months (95%CI, 4.8-16.9). For patients whose disease progressed on a prior CDK4/6i, we demonstrated comparable median TTFs for patients rechallenged with the same CDK4/6i (4.3 months, 95%CI 3.2-5.5) and with a different CDK4/6i (4.7 months, 95%CI 3.7-6.0) when compared to the recent PACE, PALMIRA, and MAINTAIN trials. Exploratory genomic analysis suggested that the presence of mutations known to confer CDK4/6i resistance, such as TP53 mutations, CDK4 amplifications, and RB1 or FAT1 loss of function mutations may be molecular biomarkers predictive of CDK4/6i retrial failure.

Clinical management of TP53 mosaic variants found on germline genetic testing.

BACKGROUND: Germline heterozygous TP53 pathogenic variants (PVs) cause Li Fraumeni Syndrome (LFS, OMIM#151623). TP53 PVs at lower-than-expected variant allele frequencies (VAF) may reflect postzygotic mosaicism (PZM) or clonal hematopoiesis (CH); however, no guidelines exist for workup and clinical management. PATIENTS AND METHODS: Retrospective analysis of probands who presented to an academic cancer genetics program with a TP53 PV result on germline genetic testing. RESULTS: Twenty-one of 125 unrelated probands (17 %) were found to harbor a TP53 PV with VAF<30 % or a designation of "mosaic". A diagnosis of PZM was made in nine (43 %) due to a clinical phenotype consistent with LFS with (n = 8) or without (n = 1) positive ancillary tissue testing. Twelve patients (57 %) were diagnosed with presumed CH (pCH) due to a diagnosis of a myeloproliferative neoplasm, negative ancillary tissue testing, clinical phenotype not meeting LFS criteria, no cancer, and/or no first cancer age<50. Of the 19 patients with biological offspring, nine had either partial or complete offspring testing, all negative. CONCLUSIONS: Determining the etiology of low VAF TP53 PVs requires ancillary tissue testing and incorporation of clinical phenotype. Discerning PZM versus CH is important to provide optimal care and follow-up.

Sequential activation of E2F via Rb degradation and c-Myc drives resistance to CDK4/6 inhibitors in breast cancer.

Cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) are key therapeutic agents in the management of metastatic hormone-receptor-positive breast cancer. However, the emergence of drug resistance limits their long-term efficacy. Here, we show that breast cancer cells develop CDK4/6i resistance via a sequential two-step process of E2F activation. This process entails retinoblastoma (Rb)-protein degradation, followed by c-Myc-mediated amplification of E2F transcriptional activity. CDK4/6i treatment halts cell proliferation in an Rb-dependent manner but dramatically reduces Rb-protein levels. However, this reduction in Rb levels insufficiently induces E2F activity. To develop CDK4/6i resistance, upregulation or activating mutations in mitogenic or hormone signaling are required to stabilize c-Myc levels, thereby augmenting E2F activity. Our analysis of pre-treatment tumor samples reveals a strong correlation between c-Myc levels, rather than Rb levels, and poor therapeutic outcomes after CDK4/6i treatment. Moreover, we propose that proteasome inhibitors can potentially reverse CDK4/6i resistance by restoring Rb levels.

A genotype-first approach identifies high incidence of NF1 pathogenic variants with distinct disease associations.

Loss of function variants in the NF1 gene cause neurofibromatosis type 1 (NF1), a genetic disorder characterized by complete penetrance, prevalence of 1 in 3,000, characteristic physical exam findings, and a substantially increased risk for malignancy. However, our understanding of the disorder is entirely based on patients ascertained through phenotype-first approaches. Leveraging a genotype-first approach in two large patient cohorts, we demonstrate unexpectedly high prevalence (1 in 450-750) of NF1 pathogenic variants. Half were identified in individuals lacking clinical features of NF1, with many appearing to have post-zygotic mosaicism for the identified variant. Incidentally discovered variants were not associated with classic NF1 features but were associated with an increased incidence of malignancy compared to a control population. Our findings suggest that NF1 pathogenic variants are substantially more common than previously thought, often characterized by somatic mosaicism and reduced penetrance, and are important contributors to cancer risk in the general population.

Genetic Ancestry Correlates with Somatic Differences in a Real-World Clinical Cancer Sequencing Cohort.

Accurate ancestry inference is critical for identifying genetic contributors of cancer disparities among populations. Although methods to infer genetic ancestry have historically relied upon genome-wide markers, the adaptation to targeted clinical sequencing panels presents an opportunity to incorporate ancestry inference into routine diagnostic workflows. We show that global ancestral contributions and admixture of continental populations can be quantitatively inferred using markers captured by the MSK-IMPACT clinical panel. In a pan-cancer cohort of 45,157 patients, we observed differences by ancestry in the frequency of somatic alterations, recapitulating known associations and revealing novel associations. Despite the comparable overall prevalence of driver alterations by ancestry group, the proportion of patients with clinically actionable alterations was lower for African (30%) compared with European (33%) ancestry. Although this result is largely explained by population-specific cancer subtype differences, it reveals an inequity in the degree to which different populations are served by existing precision oncology interventions. SIGNIFICANCE: We performed a comprehensive analysis of ancestral associations with somatic mutations in a real-world pan-cancer cohort, including >5,000 non-European individuals. Using an FDA-authorized tumor sequencing panel and an FDA-recognized oncology knowledge base, we detected differences in the prevalence of clinically actionable alterations, potentially contributing to health care disparities affecting underrepresented populations. This article is highlighted in the In This Issue feature, p. 2483.

Genomic characterization of metastatic patterns from prospective clinical sequencing of 25,000 patients.

Metastatic progression is the main cause of death in cancer patients, whereas the underlying genomic mechanisms driving metastasis remain largely unknown. Here, we assembled MSK-MET, a pan-cancer cohort of over 25,000 patients with metastatic diseases. By analyzing genomic and clinical data from this cohort, we identified associations between genomic alterations and patterns of metastatic dissemination across 50 tumor types. We found that chromosomal instability is strongly correlated with metastatic burden in some tumor types, including prostate adenocarcinoma, lung adenocarcinoma, and HR+/HER2+ breast ductal carcinoma, but not in others, including colorectal cancer and high-grade serous ovarian cancer, where copy-number alteration patterns may be established early in tumor development. We also identified somatic alterations associated with metastatic burden and specific target organs. Our data offer a valuable resource for the investigation of the biological basis for metastatic spread and highlight the complex role of chromosomal instability in cancer progression.

HER2 + breast cancers evade anti-HER2 therapy via a switch in driver pathway.

Inhibition of HER2 in HER2-amplified breast cancer has been remarkably successful clinically, as demonstrated by the efficacy of HER-kinase inhibitors and HER2-antibody treatments. Whilst resistance to HER2 inhibition is common in the metastatic setting, the specific programs downstream of HER2 driving resistance are not established. Through genomic profiling of 733 HER2-amplified breast cancers, we identify enrichment of somatic alterations that promote MEK/ERK signaling in metastatic tumors with shortened progression-free survival on anti-HER2 therapy. These mutations, including NF1 loss and ERBB2 activating mutations, are sufficient to mediate resistance to FDA-approved HER2 kinase inhibitors including tucatinib and neratinib. Moreover, resistant tumors lose AKT dependence while undergoing a dramatic sensitization to MEK/ERK inhibition. Mechanistically, this driver pathway switch is a result of MEK-dependent activation of CDK2 kinase. These results establish genetic activation of MAPK as a recurrent mechanism of anti-HER2 therapy resistance that may be effectively combated with MEK/ERK inhibitors.

Clonal hematopoiesis is associated with risk of severe Covid-19.

Acquired somatic mutations in hematopoietic stem and progenitor cells (clonal hematopoiesis or CH) are associated with advanced age, increased risk of cardiovascular and malignant diseases, and decreased overall survival. These adverse sequelae may be mediated by altered inflammatory profiles observed in patients with CH. A pro-inflammatory immunologic profile is also associated with worse outcomes of certain infections, including SARS-CoV-2 and its associated disease Covid-19. Whether CH predisposes to severe Covid-19 or other infections is unknown. Among 525 individuals with Covid-19 from Memorial Sloan Kettering (MSK) and the Korean Clonal Hematopoiesis (KoCH) consortia, we show that CH is associated with severe Covid-19 outcomes (OR = 1.85, 95%=1.15-2.99, p = 0.01), in particular CH characterized by non-cancer driver mutations (OR = 2.01, 95% CI = 1.15-3.50, p = 0.01). We further explore the relationship between CH and risk of other infections in 14,211 solid tumor patients at MSK. CH is significantly associated with risk of Clostridium Difficile (HR = 2.01, 95% CI: 1.22-3.30, p = 6×10-3) and Streptococcus/Enterococcus infections (HR = 1.56, 95% CI = 1.15-2.13, p = 5×10-3). These findings suggest a relationship between CH and risk of severe infections that warrants further investigation.

Clonal hematopoiesis is associated with risk of severe Covid-19.

Acquired somatic mutations in hematopoietic stem and progenitor cells (clonal hematopoiesis or CH) are associated with advanced age, increased risk of cardiovascular and malignant diseases, and decreased overall survival. 1-4 These adverse sequelae may be mediated by altered inflammatory profiles observed in patients with CH. 2,5,6 A pro-inflammatory immunologic profile is also associated with worse outcomes of certain infections, including SARS-CoV-2 and its associated disease Covid-19. 7,8 Whether CH predisposes to severe Covid-19 or other infections is unknown. Among 515 individuals with Covid-19 from Memorial Sloan Kettering (MSK) and the Korean Clonal Hematopoiesis (KoCH) consortia, we found that CH was associated with severe Covid-19 outcomes (OR=1.9, 95%=1.2-2.9, p=0.01). We further explored the relationship between CH and risk of other infections in 14,211 solid tumor patients at MSK. CH was significantly associated with risk of Clostridium Difficile (HR=2.0, 95% CI: 1.2-3.3, p=6×10 -3 ) and Streptococcus/Enterococcus infections (HR=1.5, 95% CI=1.1-2.1, p=5×10 -3 ). These findings suggest a relationship between CH and risk of severe infections that warrants further investigation.

Examining the cost-effectiveness of baseline left ventricular function assessment among breast cancer patients undergoing anthracycline-based therapy.

BACKGROUND: There is a lack of consensus to guide which breast cancer patients require left ventricular function assessment (LVEF) prior to anthracycline therapy; the cost-effectiveness of screening this patient population has not been previously evaluated. METHODS: We performed a retrospective analysis of the Yale Nuclear Cardiology Database, including 702 patients with baseline equilibrium radionuclide angiography (ERNA) scan prior to anthracycline and/or trastuzumab therapy. We sought to examine associations between abnormal baseline LVEF and potential cardiac risk factors. Additionally, we designed a Markov model to determine the incremental cost-effectiveness ratio (ICER) of ERNA screening for women aged 55 with stage I-III breast cancer from a payer perspective over a lifetime horizon. RESULTS: An abnormal LVEF was observed in 2% (n = 14) of patients. There were no significant associations on multivariate analysis performed on self-reported risk factors. Our analysis showed LVEF screening is cost-effective with ICER of $45,473 per QALY gained. For a willingness-to-pay threshold of $100,000/ QALY, LVEF screening had an 81.9% probability of being cost-effective. Under the same threshold, screening was cost-effective for non-anthracycline cardiotoxicity risk of RR ≤ 0.58, as compared to anthracycline regimens. CONCLUSIONS: Age, preexisting cardiac risk factors and coronary artery disease did not predict a baseline abnormal LVEF. While the prevalence of an abnormal baseline LVEF is low in patients with breast cancer, our results suggest that cardiac screening prior to anthracycline is cost-effective.

Immune microenvironment of triple-negative breast cancer in African-American and Caucasian women.

PURPOSE: African-American (AA) patients with triple-negative breast cancer (TNBC) are less likely to achieve pathologic complete response from neoadjuvant chemotherapy and have poorer prognosis than Caucasian patients with TNBC, suggesting potential biological differences by race. Immune infiltration is the most consistent predictive marker for chemotherapy response and improved prognosis in TNBC. In this study, we test the hypothesis that the immune microenvironment differs between AA and Caucasian patients. METHODS: RNA-seq expression data were obtained from The Cancer Genome Atlas (TCGA) database for 162 AA and 697 Caucasian breast cancers. Estrogen receptor (ER)-positive, human epidermal growth factor receptor-2 (HER2)-positive, and TNBC subtypes were included in the analyses. Tumor infiltrating lymphocyte (TIL) counts, immunomodulatory scores, and molecular subtypes were obtained from prior publications for a subset of the TNBC cases. Differences in immune cell distributions and immune functions, measured through gene expression and TIL counts, as well as neoantigen, somatic mutation, amplification, and deletion loads, were compared by race and tumor subtype. RESULTS: Immune metagene analysis demonstrated marginal immune attenuation in AA TNBC relative to Caucasian TNBC that did not reach statistical significance. The distributions of immune cell populations, lymphocyte infiltration, molecular subtypes, and genomic aberrations between AA and Caucasian subtypes were also not significantly different. The MHC1 metagene demonstrated increased expression in AA ER-positive cancers relative to Caucasian ER-positive cancers. CONCLUSIONS: This study suggests that the immunological differences between AA and Caucasian breast cancers represented by TCGA data are subtle, if they exist at all. We observed no consistent racial differences in immune gene expression or TIL counts in TNBC by race. However, this study cannot rule out small differences in immune cell subtype distribution and activity status that may not be apparent in bulk RNA analysis.

Immune Gene Expression Is Associated with Genomic Aberrations in Breast Cancer.

The presence of tumor-infiltrating lymphocytes (TIL) is a favorable prognostic factor in breast cancer, but what drives immune infiltration remains unknown. Here we examine if clonal heterogeneity, total mutation load, neoantigen load, copy number variations (CNV), gene- or pathway-level somatic mutations, or germline polymorphisms (SNP) are associated with immune metagene expression in breast cancer subtypes. Thirteen published immune metagenes correlated separately with genomic metrics in the three major breast cancer subtypes. We analyzed RNA-Seq, DNA copy number, mutation and germline SNP data of 627 ER+, 207 HER2+, and 191 triple-negative (TNBC) cancers from The Cancer Genome Atlas. P-values were adjusted for multiple comparisons, and permutation testing was used to assess false discovery rates. Increased immune metagene expression associated significantly with lower clonal heterogeneity estimated by MATH score in all subtypes and with a trend for lower overall mutation, neoantigen, and CNV loads in TNBC and HER2+ cancers. In ER+ cancers, mutation load, neoantigen load, and CNV load weakly but positively associated with immune infiltration, which reached significance for overall mutation load only. No highly recurrent single gene or pathway level mutations associated with immune infiltration. High immune gene expression and lower clonal heterogeneity in TNBC and HER2+ cancers suggest an immune pruning effect and equilibrium between immune surveillance and clonal expansion. Thus, immune checkpoint inhibitors may tip the balance in favor of immune surveillance in these cancers. Cancer Res; 77(12); 3317-24. ©2017 AACR.

Systematic Drug Screening Identifies Tractable Targeted Combination Therapies in Triple-Negative Breast Cancer.

Triple-negative breast cancer (TNBC) remains an aggressive disease without effective targeted therapies. In this study, we addressed this challenge by testing 128 FDA-approved or investigational drugs as either single agents or in 768 pairwise drug combinations in TNBC cell lines to identify synergistic combinations tractable to clinical translation. Medium-throughput results were scrutinized and extensively analyzed for sensitivity patterns, synergy, anticancer activity, and were validated in low-throughput experiments. Principal component analysis revealed that a fraction of all upregulated or downregulated genes of a particular targeted pathway could partly explain cell sensitivity toward agents targeting that pathway. Combination therapies deemed immediately tractable to translation included ABT-263/crizotinib, ABT-263/paclitaxel, paclitaxel/JQ1, ABT-263/XL-184, and paclitaxel/nutlin-3, all of which exhibited synergistic antiproliferative and apoptotic activity in multiple TNBC backgrounds. Mechanistic investigations of the ABT-263/crizotinib combination offering a potentially rapid path to clinic demonstrated RTK blockade, inhibition of mitogenic signaling, and proapoptotic signal induction in basal and mesenchymal stem-like TNBC. Our findings provide preclinical proof of concept for several combination treatments of TNBC, which offer near-term prospects for clinical translation. Cancer Res; 77(2); 566-78. ©2016 AACR.

New Strategies in Breast Cancer: Immunotherapy.

More than 70% of breast cancers contain lymphocytic infiltration in the stroma, and preclinical studies suggest that immunoediting and partial control of cancer progression by the local immune microenvironment operate in most breast cancers. Consistent with this hypothesis, a large number of studies demonstrated a favorable prognostic and chemotherapy response predictive role for immune infiltration in breast cancer. The evidence is particularly strong for triple-negative and HER2-positive cancers. The development of clinically effective immune checkpoint inhibitors now provides an opportunity to test the therapeutic potential of augmenting the local antitumor immune response. Several phase I clinical trials using single-agent anti-PD-1 and anti-PD-L1 antibodies demonstrated objective tumor response rates, with remarkably durable responses, in heavily pretreated, metastatic, triple-negative cancers and somewhat lower responses in estrogen receptor-positive cancers. Currently, close to 50 ongoing, or soon to open, clinical trials evaluate the role of this new treatment modality in breast cancer. Clin Cancer Res; 22(9); 2105-10. ©2016 AACR.

Assessing cost-utility of predictive biomarkers in oncology: a streamlined approach.

Evaluation of cost-utility is critical in assessing the medical utility of predictive or prognostic biomarkers. Current methods involve complex state-transition models, requiring comprehensive data inputs. We propose a simplified decision-analytic tool to explore the relative effect of factors contributing to the cost-utility of a biomarker. We derived a cost-utility metric, the "test incremental cost-effectiveness ratio" (TICER) for biomarker-guided treatment compared to no biomarker use. This method uses data inputs readily accessible through clinical literature. We compared our results with traditional cost-effectiveness analysis of predictive biomarkers for established (HER2-guided trastuzumab, ALK-guided crizotinib, OncotypeDX-guided adjuvant chemotherapy) and emerging (ROS1-guided crizotinib) targeted treatments. We conducted sensitivity analysis to determine which factors had the greatest impact on TICER estimates. Base case TICER for HER2 was $149,600/quality-adjusted life year (QALY), for ALK was $22,200/QALY, and for OncotypeDX was $11,600/QALY, consistent with literature-reported estimates ($180,000/QALY, $202,800/QALY, $8900/QALY, respectively). Base case TICER for ROS1-guided crizotinib was $205,900/QALY. Generally, when treatment cost is considerably greater than biomarker testing costs, TICER is driven by clinical outcomes and health-related quality of life, while biomarker prevalence and treatment cost have a lesser effect. Our simplified decision-analytic approach produces values consistent with existing cost-effectiveness analyses. Our results suggest that biomarker value is mostly driven by the clinical efficacy of the targeted agent. A user-friendly web tool for complete TICER analysis has been made available for open use at http://medicine.yale.edu/lab/pusztai/ticer/ .