First evidence of AXL expression on circulating tumor cells in metastatic breast cancer patients: A proof-of-concept study

BACKGROUND

For several years, the AXL tyrosine kinase receptor, a member of the Tyro3-Axl-Mer (TAM) family, has been considered a new strategic target in oncology. AXL overexpression is common in solid tumors and is associated with poor prognosis. In this context, the detection of a subset of circulating tumor cells (CTCs) that express AXL (AXL+ CTCs) could be clinically relevant.

METHODS

Immunostaining was performed to assess AXL expression in human breast cancer cell lines. The optimal conditions were established using flow cytometry. Spiking experiments were carried out to optimize the parameters of the CellSearch® system detection test. CTC enumeration and AXL expression were evaluated in patients with metastatic breast cancer (mBC) before treatment initiation.

RESULTS

An innovative AXL+ CTC detection assay to be used with the CellSearch® system was developed. In a prospective longitudinal clinical trial, blood samples from 60 patients with untreated mBC were analyzed to detect AXL+ CTCs with this new assay. CTCs were detected in 35/60 patients (58.3%) and AXL+ CTCs were identified in 7 of these 35 patients (11.7% of all patients).

CONCLUSION

This newly established AXL+ CTC assay is a promising tool that can be used for liquid biopsy in future clinical trials to stratify and monitor patients with cancer receiving anti-AXL therapies.

Contraception in breast cancer survivors from the FEERIC case-control study (performed on behalf of the Seintinelles research network)

OBJECTIVE

To compare the prevalence of contraception in breast cancer (BC) patients at risk of unintentional pregnancy (i.e. not currently pregnant or trying to get pregnant) and matched controls.

STUDY DESIGN

The FEERIC study (Fertility, Pregnancy, Contraception after BC in France) is a prospective, multicenter case-control study, including localized BC patients aged 18-43 years, matched for age and parity to cancer-free volunteer controls in a 1:2 ratio. Data were collected through online questionnaires completed on the Seintinelles research platform.

RESULTS

In a population of 1278 women at risk of unintentional pregnancy, the prevalence of contraception at study inclusion did not differ significantly between cases (340/431, 78.9%) and controls (666/847, 78.6%, p = 0.97). Contrarily, the contraceptive methods used were significantly different, with a higher proportion of copper IUD use in BC survivors (59.5% versus 25.0% in controls p < 0.001). For patients at risk of unintentional pregnancy, receiving information about chemotherapy-induced ovary damage at BC diagnosis (OR = 2.47 95%CI [ 1.39-4.37] and anti-HER2 treatment (OR = 2.46, 95% CI [ 1.14-6.16]) were significantly associated with the use of a contraception in multivariate analysis.

CONCLUSION

In this large French study, BC survivors had a prevalence of contraception use similar to that for matched controls, though almost one in five women at risk of unintentional pregnancy did not use contraception. Dedicated consultations at cancer care centers could further improve access to information and contraception counseling.

Correlation of the TIGIT-PVR immune checkpoint axis with clinicopathological features in triple-negative breast cancer

Background

T cell immunoreceptor with Ig and ITIM domains (TIGIT) interacts with poliovirus receptor (PVR) to contribute to cancer immune escape. Recently, TIGIT and PVR have been identified as promising immunotherapy targets. Their gene expression is upregulated in many solid tumors, but their protein expression level is not well documented, particularly in triple negative breast cancer (TNBC), the breast cancer subtype that most benefit from immunotherapy.

Methods

TIGIT and PVR expression levels were assessed by immunohistochemistry in 243 surgically resected localized TNBC and then their relationship with clinical-pathological features and clinical outcome was analyzed.

Results

TIGIT expression was observed in immune cells from the tumor microenvironment, whereas PVR was mainly expressed by tumor cells. High TIGIT expression was significantly associated with age (p=0.010), histological grade (p=0.014), non-lobular histology (p=0.024), adjuvant chemotherapy (p=0.006), and various immune cell populations (tumor infiltrating lymphocytes (TILs), CD3⁺, CD8⁺, PD-1⁺ cells; all p<0.0001), PD-L1⁺ tumor cells (p<0.0001), and PD-L1⁺ stromal cells (p=0.003). Infiltration by TIGIT⁺ cells tended to be higher in non-molecular apocrine tumors (p=0.088). PVR was significantly associated with histological grade (p<0.0001), the basal-like (p=0.003) and non-molecular apocrine phenotypes (p=0.039), high TILs infiltration (p=0.011), CD3⁺ (p=0.002), CD8⁺ (p=0.024) T cells, and PD-L1 expression in tumor (p=0.003) and stromal cells (p=0.001). In univariate analysis, only known prognostic factors (age, tumor size, lymph node status, adjuvant chemotherapy, TILs and CD3⁺ T-cell infiltrate) were significantly associated with relapse-free survival (RFS) and overall survival. High TIGIT and PVR expression levels tended to be associated with longer RFS (p=0.079 and 0.045, respectively). The analysis that included only non-molecular apocrine TNBC revealed longer RFS for tumors that strongly expressed TIGIT or PVR (p=0.025 for TIGIT and 0.032 for PVR).

Conclusions

These results indicated that in TNBC, TIGIT⁺ cells can easily interact with PVR to exert their inhibitory effects. Their wide expression in TNBC and their association with other immune checkpoint components suggest the therapeutic interest of the TIGIT-PVR axis.

Text Mining in Electronic Medical Records Enables Quick and Efficient Identification of Pregnancy Cases Occurring After Breast Cancer

PURPOSE

To apply text mining (TM) technology on electronic medical records (EMRs) of patients with breast cancer (BC) to retrieve the occurrence of a pregnancy after BC diagnosis and compare its performance to manual curation.

MATERIALS AND METHODS

The training cohort (Cohort A) comprised 344 patients with BC age ≤ 40 years old treated at Institut Curie between 2005 and 2007. Manual curation consisted in manually reviewing each EMR to retrieve pregnancies. TM consisted of first applying a keyword filter ("accouch*" or "enceinte," French terms for "deliver*" and "pregnant," respectively) to select a subset of EMRs, and, second, checking manually EMRs to confirm the pregnancy. Then, we applied our TM algorithm on an independent cohort of patients with BC treated between 2008 and 2012 (Cohort B).

RESULTS

In Cohort A, 36 pregnancies were identified among 344 patients (10.5%; 2,829 person-years of EMR). Thirty were identified by manual review versus 35 by TM. TM resulted in a lower percentage of manual checking (26.7% v 100%, respectively) and substantial time gains (time to identify a pregnancy: 13 minutes for TM v 244 minutes for manual curation, respectively). Presence of any of the two TM filters showed excellent sensitivity (97%) and negative predictive value (100%). In Cohort B, 67 pregnancies were identified among 1,226 patients (5.5%; 7,349 person-years of EMR). Similarly, for Cohort B, TM spared 904 (73.7%) EMRs from manual review and quickly generated a cohort of 67 pregnancies after BC. Incidence rate of pregnancy after BC was 0.01 pregnancy per person-year of EMR in both cohorts.

CONCLUSION

TM is highly efficient to quickly identify rare events and is a promising tool to improve rapidity, efficiency, and costs of medical research.

Unraveling the physiological functions of exosome secretion by tumors

To understand the physiological functions of exosomes, we have recently used the inhibition of Rab27a, which prevents exosome release but also alters other secretion pathways. Our work demonstrates that the secretion of exosomes by some tumors in vivo can influence the immune microenvironment to promote tumor progression, but also that this phenomenon cannot be generalized to all tumors and all exosomes.

Rab27a supports exosome-dependent and -independent mechanisms that modify the tumor microenvironment and can promote tumor progression

During progression from single cancer cells to a tumor mass and metastases, tumor cells send signals that can subvert their tissue microenvironment. These signals involve soluble molecules and various extracellular vesicles, including a particular type termed exosomes. The specific roles of exosomes secreted in the tumor microenvironment, however, is unclear. The small GTPases RAB27A and RAB27B regulate exocytosis of multivesicular endosomes, which lead to exosome secretion, in human HeLa cells. Here, we used mouse models to show that Rab27a blockade in mammary carcinoma cells decreased secretion of exosomes characterized by endocytic markers, but also of matrix metalloproteinase 9, which is not associated with exosomes. Rab27a blockade resulted in decreased primary tumor growth and lung dissemination of a metastatic carcinoma (4T1), but not of a nonmetastatic carcinoma (TS/A). Local growth of 4T1 tumors required mobilization of a population of neutrophil immune cells induced by Rab27a-dependent secretion of exosomes together with a specific combination of cytokines and/or metalloproteinases. Our findings offer in vivo validation of the concept that exosome secretion can exert key pathophysiologic roles during tumor formation and progression, but they also highlight the idiosyncratic character of the tumor context.

Diverse subpopulations of vesicles secreted by different intracellular mechanisms are present in exosome preparations obtained by differential ultracentrifugation

Exosomes are extracellular vesicles of 50 to 100 nm in diameter, released by many cell types. Exosomes are formed inside the cell in intracellular endosomal compartments and are secreted upon fusion of these compartments with the plasma membrane. Cells also secrete other types of membrane vesicles, for instance, by outward budding from the plasma membrane, and although some of them clearly differ from exosomes by their structural features (larger size), others are possibly more difficult to separate. Here, using Rab27a inhibition to modulate exosome secretion, we show the existence of at least 2 distinct populations of vesicles after purification by classical ultracentrifugation from mouse tumor cell conditioned medium. Rab27a inhibition lead to decreased vesicular secretion of some conventional markers of exosomes (CD63, Tsg101, Alix and Hsc70) but did not affect secretion of others (CD9 and Mfge8). By electron microscopy, CD9 was observed on vesicles of various sizes, ranging from 30 nm to more than 150 nm in diameter. Flotation onto sucrose gradients showed different proportions of CD63, CD9 and Mfge8 not only in fractions of densities classically described for exosomes (around 1.15 g/ml) but also in fractions of densities over 1.20 g/ml, indicating the presence of heterogenous vesicle populations. CD9 and Mfge8 were also found in large vesicles pelleted at low speed and can thus not be considered as specific components of endosome-derived vesicles. We propose that the most commonly used protocols for exosome preparations co-purify vesicles from endosomal and other origins, possibly the plasma membrane. Future work will be required to improve techniques for accurate purification and characterization of the different populations of extracellular vesicles.

Targeting tumor antigens to secreted membrane vesicles in vivo induces efficient antitumor immune responses

Expression of non-self antigens by tumors can induce activation of T cells in vivo, although this activation can lead to either immunity or tolerance. CD8+ T-cell activation can be direct (if the tumor expresses MHC class I molecules) or indirect (after the capture and cross-presentation of tumor antigens by dendritic cells). The modes of tumor antigen capture by dendritic cells in vivo remain unclear. Here we examine the immunogenicity of the same model antigen secreted by live tumors either in association with membrane vesicles (exosomes) or as a soluble protein. We have artificially addressed the antigen to secreted vesicles by coupling it to the factor VIII-like C1C2 domain of milk fat globule epidermal growth factor-factor VIII (MFG-E8)/lactadherin. We show that murine fibrosarcoma tumor cells that secrete vesicle-bound antigen grow slower than tumors that secrete soluble antigen in immunocompetent, but not in immunodeficient, host mice. This growth difference is due to the induction of a more potent antigen-specific antitumor immune response in vivo by the vesicle-bound than by the soluble antigen. Finally, in vivo secretion of the vesicle-bound antigen either by tumors or by vaccination with naked DNA protects against soluble antigen-secreting tumors. We conclude that the mode of secretion can determine the immunogenicity of tumor antigens and that manipulation of the mode of antigen secretion may be used to optimize antitumor vaccination protocols.