Involvement of the kynurenine pathway in breast cancer: updates on clinical research and trials

Breast cancer (BrCa) is the leading cause of cancer incidence and mortality in women worldwide. While BrCa treatment has been shown to be highly successful if detected at an early stage, there are few effective strategies to treat metastatic tumours. Hence, metastasis remains the main cause in most of BrCa deaths, highlighting the need for new approaches in this group of patients. Immunotherapy has been gaining attention as a new treatment for BrCa metastasis and the kynurenine pathway (KP) has been suggested as one of the potential targets. The KP is the major biochemical pathway in tryptophan (TRP) metabolism, catabolising TRP to nicotinamide adenine dinucleotide (NAD+). The KP has been reported to be elevated under inflammatory conditions such as cancers and that its activity suppresses immune surveillance. Dysregulation of the KP has previously been reported implicated in BrCa. This review aims to discuss and provide an update on the current mechanisms involved in KP-mediated immune suppression and cancer growth. Furthermore, we also provide a summary on 58 studies about the involvement of the KP and BrCa and five clinical trials targeting KP enzymes and their outcome.

Differential kynurenine pathway metabolism in highly metastatic aggressive breast cancer subtypes: beyond IDO1-induced immunosuppression

Background

Immunotherapy has recently been proposed as a promising treatment to stop breast cancer (BrCa) progression and metastasis. However, there has been limited success in the treatment of BrCa with immune checkpoint inhibitors. This implies that BrCa tumors have other mechanisms to escape immune surveillance. While the kynurenine pathway (KP) is known to be a key player mediating tumor immune evasion and while there are several studies on the roles of the KP in cancer, little is known about KP involvement in BrCa.

Methods

To understand how KP is regulated in BrCa, we examined the KP profile in BrCa cell lines and clinical samples (n = 1997) that represent major subtypes of BrCa (luminal, HER2-enriched, and triple-negative (TN)). We carried out qPCR, western blot/immunohistochemistry, and ultra-high pressure liquid chromatography on these samples to quantify the KP enzyme gene, protein, and activity, respectively.

Results

We revealed that the KP is highly dysregulated in the HER2-enriched and TN BrCa subtype. Gene, protein expression, and KP metabolomic profiling have shown that the downstream KP enzymes KMO and KYNU are highly upregulated in the HER2-enriched and TN BrCa subtypes, leading to increased production of the potent immunosuppressive metabolites anthranilic acid (AA) and 3-hydroxylanthranilic acid (3HAA).

Conclusions

Our findings suggest that KMO and KYNU inhibitors may represent new promising therapeutic targets for BrCa. We also showed that KP metabolite profiling can be used as an accurate biomarker for BrCa subtyping, as we successfully discriminated TN BrCa from other BrCa subtypes.

Stromal cell diversity associated with immune evasion in human triple-negative breast cancer

The tumour stroma regulates nearly all stages of carcinogenesis. Stromal heterogeneity in human triple-negative breast cancers (TNBCs) remains poorly understood, limiting the development of stromal-targeted therapies. Single-cell RNA sequencing of five TNBCs revealed two cancer-associated fibroblast (CAF) and two perivascular-like (PVL) subpopulations. CAFs clustered into two states: the first with features of myofibroblasts and the second characterised by high expression of growth factors and immunomodulatory molecules. PVL cells clustered into two states consistent with a differentiated and immature phenotype. We showed that these stromal states have distinct morphologies, spatial relationships and functional properties in regulating the extracellular matrix. Using cell signalling predictions, we provide evidence that stromal-immune crosstalk acts via a diverse array of immunoregulatory molecules. Importantly, the investigation of gene signatures from inflammatory-CAFs and differentiated-PVL cells in independent TNBC patient cohorts revealed strong associations with cytotoxic T-cell dysfunction and exclusion, respectively. Such insights present promising candidates to further investigate for new therapeutic strategies in the treatment of TNBCs.

Programmed death ligand 1 expression in triple-negative breast cancer is associated with tumour-infiltrating lymphocytes and improved outcome

AIMS

Triple-negative breast cancer (TNBC) patients generally have a poor outcome; there is a pressing need to identify more effective therapeutic strategies. Clinical trials targeting programmed death 1/programmed death ligand 1 (PD1/PDL1) in melanoma and non-small-cell lung cancer have reported high response rates, and tumoral PDL1 expression has been suggested as a potential biomarker to enrich for patient response to these treatments. There are only very limited data to date reporting the expression of PDL1 in TNBC.

METHODS AND RESULTS

PDL1 immunohistochemistry was performed on 161 primary TNBCs and assessed in the tumour as well as immune cells in the stromal compartment. PDL1 expression was very common in TNBC, expressed in the tumour cell membrane (64%), cytoplasm (80%) and stromal (93%) cellular compartments. Cytoplasmic tumoral expression of PDL1 was associated with a lower risk of breast cancer-specific death [hazard ratio (HR) 0.45, P = 0.035] while stromal PDL1 expression was associated with a lower rate of deaths from all causes (HR 0.305, P = 0.0042). Membranous expression of PDL1 was not associated with outcome. While both PDL1 expression and tumour-infiltrating lymphocytes were associated with a better outcome, only lymphovascular invasion and high tumour-infiltrating lymphocytes were independently prognostic for breast cancer-specific death.

CONCLUSION

While PDL1 expression is frequent in TNBC, it was not independently prognostic. There were differences in outcome depending on the cellular compartment of PDL1 expression. These data provide further impetus for investigating the utility of immune checkpoint therapies in TNBC, given the clinical significance of tumour-infiltrating lymphocytes (TILs) and PDL1 expression in this cohort.

Microscopic diffusion properties of fixed breast tissue: Preliminary findings

PURPOSE

To investigate the microscopic diffusion properties of formalin-fixed breast tissue.

METHODS

Diffusion microimaging was performed at 16.4T with 40-μm isotropic voxels on two normal and two cancer tissue samples from four patients. Results were correlated with histology of the samples.

RESULTS

Diffusion-weighted images and mean diffusivity maps demonstrated distinct diffusivity differences between breast tissue components. Mean diffusivity (MD) in normal tissue was 0.59 ± 0.24 μm(2) /ms for gland lobule (voxels containing epithelium and intralobular stroma) and 1.23 ± 0.34 μm(2) /ms for interlobular fibrous stroma. In the cancer samples, MD = 0.45 ± 0.23 μm(2) /ms for invasive ductal carcinoma (voxels contain epithelium and intralobular stroma) and 0.61 ± 0.35 μm(2) /ms for ductal carcinoma in situ. There were significant MD differences between all tissue components (P < 0.005), except between gland lobule and ductal carcinoma in situ (P = 0.71). The low diffusivity of epithelium-rich cancer tissue and of normal epithelium relative to its supporting fibrous stroma was similar to that reported for prostate tissue and the esophageal wall.

CONCLUSION

Diffusion microimaging demonstrates distinct diffusivity differences between breast tissue glandular structures. Low diffusivity may be a distinctive feature of mammalian epithelia.

Cell cycle marker expression in benign and malignant intraductal papillary lesions of the breast

AIMS

The diagnosis of intraductal papillary lesions of the breast on core biopsy remains challenging in pathology, with most patients requiring formal surgical excision for a definitive diagnosis. The aim of this study was to determine whether a representative panel of proliferative cell cycle immunohistochemical markers (cyclin A2, cyclin B1 and cyclin D1) could improve the specificity of pathological diagnosis of these lesions.

METHODS

A series of 68 surgically excised intraductal papillary lesion cases were retrospectively selected, and immunohistochemistry for cyclin A2, cyclin B1 and cyclin D1 was performed.

RESULTS

Cyclin B1 (OR 1.80, 95% CI 1.01 to 3.2, p=0.046) and cyclin D1 (OR 1.13, 95% CI 1.05 to 1.22, p=0.002) expression was independently associated with a diagnosis of malignancy in papillary lesions, although expression was frequently heterogeneous and only focal. Cyclin A2 expression (OR 0.76, 95% CI 0.41 to 1.4, p=0.38) was not associated with a malignant diagnosis in multivariable logistic regression models. All three cyclins displayed high sensitivity (80%-95%) for a diagnosis of malignancy, although cyclin B1 showed a superior specificity of 72.7% compared with the low specificity of cyclins A2 and D1.

CONCLUSIONS

Our study has identified for the first time that the expression of key cell cycle markers differs between benign and malignant papillary breast lesions and identified changes to the mitotic marker, cyclin B1, as particularly significant. However, given the low level and heterogeneous nature of expression of these markers, there remains a significant risk of undersampling in core biopsies and thus they are unlikely to be useful in routine clinical practice.

Tubular carcinoma of the breast: axillary involvement and prognostic factors

BACKGROUND

Tubular carcinoma (TC) of the breast has a very favourable prognosis. The role for axillary staging in small TC was questioned. This study investigated the frequency of axillary metastases and prognostic factors in pure TC of the breast. It involved a retrospective review of prospectively collected data.

METHODS

A consecutive series of patients presenting to The Strathfield Breast Centre (TSBC) between 1988 and 2011 were reviewed. Only pure TC was included. Information collected included demographics, surgery, pathology, adjuvant therapy and survival.

RESULTS

Pure TC accounted for 146 out of 6110 cases of operable breast cancer. Ninety-five per cent were node negative (micrometastases and isolated tumour cells excluded). Ninety-eight per cent of those with known oestrogen receptor status were oestrogen receptor positive. Median tumour size was 10 mm (range 1-52 mm). Ten-year survival was 97%. Twelve per cent of patients had more than one tumour (either ipsilateral or contralateral). Eight patients had recurrent disease. All were node negative. Three of these patients died of their disease.

CONCLUSION

Axillary metastases are uncommon in pure TC. Recurrent disease is not readily predicted by tumour size or node status.

SPECT/CT scans allow precise anatomical location of sentinel lymph nodes in breast cancer and redefine lymphatic drainage from the breast to the axilla

BACKGROUND

Historical studies of lymphatic drainage of the breast have suggested that the lymphatic drainage of the breast was to lymph nodes lying in the antero-pectoral group of nodes in the axilla just lateral to the pectoral muscles. The purpose of this study was to confirm this is not correct.

METHODS

The hybrid imaging method of SPECT/CT allows the exact anatomical position of the sentinel lymph node (SLN) in the axilla to be documented during pre-operative lymphoscintigraphy (LS) in patients with breast cancer. We have done this in a series of 741 patients. The Level I axillary nodes were defined as anterior, mid or posterior. This was related to the anatomical location of the primary cancer in the breast.

RESULTS

A SLN was found in the axilla in 97.8% of our patients. Just under 50% of SLNs located in the axilla were not in the anterior group and lay in the mid or posterior group of Level I axillary nodes. There was a SLN in a single node field in 460 patients (63%), two node fields in 261(36%), three node fields in 6 and four node fields in 1 patient.

CONCLUSION

Axillary lymphatic drainage from the breast is not exclusively to the anterior (or antero-pectoral) group of Level I nodes.

SYNOPSIS

SPECT/CT lymphoscintigraphy shows that the breast does not always drain to the anterior group of Level I lymph nodes in the axilla but may drain to the mid axilla and/or posterior group in about 50% of patients with breast cancer regardless of the location of the cancer in the breast. These data redefine lymph drainage from the breast to axillary lymph nodes.

Patterns of breast cancer relapse

AIMS

Although breast cancer is the major cause of cancer-related death in women, there is little comprehensive information on long-term outcomes, particularly pertaining to site of relapse. The Strathfield Breast Centre (TSBC) is a multidisciplinary breast clinic that has collected patient data prospectively over 14 years.

METHODS

All women with invasive, non-metastatic breast cancer, referred to TSBC from 1989 until 2002, were studied (n=2509). After initial treatment, patients were reviewed at 3-12-month intervals, including annual mammography and/or breast ultrasound. Information was collected on demographics, pre- and post-operative management and patient outcomes. Survival was analysed by the method of Kaplan and Meier.

RESULTS

The mean age was 58 years and median follow-up 4 years (range <1-14) with complete data for 81%. In total, 456 patients (18%) had a local, nodal or distant relapse. The most common site of first relapse was to bone (in 125 patients), followed by local recurrence (124), lung (73) and liver (57). The median interval from primary breast surgery until recurrence was 2.3 years and disease-free intervals correlated to survival (p<0.0001). After local recurrence the 5-year survival was 41%, vs. 20% for nodal and 13% for distant recurrence (p<0.0001). Following breast-conserving surgery, the 5-year disease-free survival after local recurrence was 49.4%, vs. 33.1% after chest wall recurrence (p=0.0361). Of distant relapses, bone metastases had the best prognosis, with median survival 2.4 years.

CONCLUSION

These data provide information on treatment outcomes in a multidisciplinary setting and statistical information that will be useful when discussing the fears and expectations of patients after the diagnosis of breast cancer.

Magnetic resonance in surgical oncology: II - literature review

Ex vivo and in vivo applications of magnetic resonance spectroscopy have been developed which aid in distinguishing malignant from normal tissues. Studies of breast, colon, cervix, oesophageal and prostate cancer reveal both the successes and failings of present technology. Verification that these non-invasive tests might supplant conventional histology in obtaining spatial diagnostic and chemical prognostic information remains for the time being illusive.

MAGNETIC RESONANCE IN SURGICAL ONCOLOGY: I - ON THE ORIGIN OF THE SPECTRUM

The discovery of the phenomenon of nuclear magnetic resonance occurred just 60 years ago. The profusion of subsequent discoveries in this domain has led to the development of magnetic resonance spectroscopy - refined as an analytical tool to discern molecular structure - and magnetic resonance imaging, a cornerstone of modern radiology. Observable alterations in cellular structure and metabolism can be discerned using the non-destructive chemical analysis of magnetic resonance spectroscopy in vitro or in vivo. Differences may thus be discerned between malignant and normal tissues.

Specificity of choline metabolites for in vivo diagnosis of breast cancer using 1H MRS at 1.5�T

The purpose was to determine if in vivo proton magnetic resonance spectroscopy ((1)H MRS) at 1.5 T can accurately provide the correct pathology of breast disease. Forty-three asymptomatic volunteers including three lactating mothers were examined and compared with 21 breast cancer patients. Examinations were undertaken at 1.5 T using a purpose-built transmit-receive single breast coil. Single voxel spectroscopy was undertaken using echo times of 135 and 350 ms. The broad composite resonance at 3.2 ppm, which includes contributions from choline, phosphocholine (PC), glycerophosphocholine (GPC), myo-inositol and taurine, was found not to be a unique marker for malignancy providing a diagnostic sensitivity and specificity of 80.0 and 86.0%, respectively. This was due to three of the asymptomatic volunteers and all of the lactating mothers also generating the broad composite resonance at 3.2 ppm. Optimised post-acquisitional processing of the spectra resolved a resonance at 3.22 ppm, consistent with PC, in patients with cancer. In contrast the spectra recorded for three false-positive volunteers, and the three lactating mothers had a resonance centred at 3.28 ppm (possibly taurine, myo-inositol or GPC). This improved the specificity of the test to 100%. Careful referencing of the spectra and post-acquisitional processing intended to optimise spectral resolution of in vivo MR proton spectra from human breast tissue resolves the composite choline resonance. This allows the distinction of patients with malignant disease from volunteers with a sensitivity of 80% and specificity of 100%. Therefore, resolution of the composite choline resonance into its constituent components improves the specificity of the in vivo (1)H MRS method, but does not overcome the problem of 20% false-negatives.

Intraoperative magnetic resonance: the future of surgery

Intraoperative magnetic resonance imaging (iMRI) is a new development in medicine that bridges the specialties of surgery and radiology. Deficiencies in the visualization of anatomical architecture and the perception of tumour boundaries in conventional open surgery have led to the integration of imaging within surgery. The superior soft tissue and multiplanar imaging features of magnetic resonance (MR) make this imaging modality superior to that of alternatives. The unique properties of MR to detect heat change and perfusion, and diffusion characteristics of tissue enhance the usefulness of this medium. Concurrent developments in computer aided image guidance and thermoablative technology, herald the era of minimally invasive tumour ablation. Applications have been developed for areas such as neurosurgery, general surgery, gynaecology and urology.

Diagnosis and prognosis of breast cancer by magnetic resonance spectroscopy of fine-needle aspirates analysed using a statistical classification strategy

BACKGROUND

The aim was to develop robust classifiers to analyse magnetic resonance spectroscopy (MRS) data of fine-needle aspirates taken from breast tumours. The resulting data could provide computerized, classification-based diagnosis and prognostic indicators.

METHODS

Fine-needle aspirate biopsies obtained at the time of surgery for both benign and malignant breast diseases were analysed by one-dimensional proton MRS at 8.5 Tesla. Diagnostic correlation was performed between the spectra and standard pathology reports, including the presence of vascular invasion by the primary cancer and involvement of the excised axillary lymph nodes.

RESULTS

Malignant tissue was distinguished from benign lesions with an overall accuracy of 93 per cent. From the same spectra, lymph node involvement was predicted with an overall accuracy of 95 per cent, and tumour vascular invasion with an overall accuracy of 94 per cent.

CONCLUSION

The pathology, nodal involvement and tumour vascular invasion were predicted by computerized statistical classification of the proton MRS spectrum from a fine-needle aspirate biopsy taken from the primary breast lesion.

Comparison of outcomes following transhiatal or Ivor Lewis esophagectomy for esophageal carcinoma

Transhiatal esophagectomy (THO) may be a valid alternative to the traditional Ivor Lewis (ILO) procedure, but there have been reservations about procedure mortality, nodal clearance, and survival. ILO is preferred for bulky midesophageal lesions and THO in frail patients, making randomization difficult. This retrospective study compares results of a 10-year period from January 1985 with a minimum follow-up period of 12 months. Four patients were lost to follow-up. Preoperative nutritional markers were similar in the two groups, as were the age and sex distribution. Altogether 33 ILOs and 65 THOs were performed. TNM staging was similar between groups, there being 43% stage II and 45% stage III lesions among the ILO patients and 53% stage II and 32% stage III disease in the THO group. Operating time was shorter for THO (256 +/- 58 minutes vs. 279 +/- 50 minutes) (p = 0.05); if two surgeons operated concurrently, THO could be performed 40 minutes quicker than THO or ILO performed by a single surgeon (p = 0.018). The mean initial intensive care unit stay was 2.9 days for ILO versus 1.7 days for THO (p = 0.014). The 30-day mortality was 5.1%; total in-hospital mortality was 7.1% with no difference for operation type. There were similar morbidity rates for the procedures. Kaplan-Meier survival analysis indicated no significant effect of surgical technique; there were no apparent advantages for either operation when patients were compared by tumor type or matched for stage. Hence THO is a valid alternative to ILO, particularly for stage II and III cancer.