Imaging mass spectrometry--a new and promising method to differentiate Spitz nevi from Spitzoid malignant melanomas

Congenital nevi versus metastatic melanoma in a newborn to a mother with malignant melanoma - diagnosis supported by sex chromosome analysis and Imaging Mass Spectrometry

A 37-year-old pregnant woman presented with a 2-cm irregular reddish nodule on her left upper arm during pregnancy. A biopsy from the lesion showed a 2.2-mm thick malignant melanoma with intravascular invasion, 25 mitosis/mm(2) and no ulceration. Following induction of labor, the patient underwent re-excision with sentinel lymph node biopsy. This showed no residual melanoma and no lymph node metastasis. The newborn boy had multiple pigmented lesions on the trunk, some of which were large and irregular. Two were biopsied and histologic examination showed dense dermal proliferation of medium sized melanocytes with multiple mitotic figures and no maturation with their descent into the dermis, raising suspicion of transplacental metastases. Examination of the placenta failed to show metastatic lesions. Multiplex polymerase chain reaction (PCR)-based genotyping, including testing for amelogenin locus for sex chromosome determination, demonstrated the presence of Y chromosome material in the melanocytes of the newborn's lesions excluding maternal origin. A diagnosis of congenital nevi was rendered. Subsequently, Imaging Mass Spectrometric analysis of the mother's lesion showed proteomic signature expression indicative of malignant melanoma, whereas the two lesions in the newborn showed changes indicative of nevi. This case demonstrates the utility of genotyping and Mass Spectrometry analysis in this challenging clinical scenario.

Comparison of the expression of vimentin and actin in spitz nevi and spitzoid malignant melanomas

INTRODUCTION

The differentiation between Spitz nevi (SN) and Spitzoid malignant melanomas (SMM) represents a challenge to dermatopathologists. We recently demonstrated differential expression of vimentin and Actin in SN and SMM by mass spectrometry (MS). We sought to investigate whether this differential expression could be detected using conventional immunohistochemistry or automated quantitative analysis (AQUA) of histological sections.

METHODS

Cases of SN and SMM, which were previously studied by MS and have readily available blocks and enough material in the block, were selected from the Yale Spitzoid Neoplasm Repository. The cases were stained for vimentin and muscle-specific actin using standard protocols. H-scores were calculated by multiplying the percentage of cells staining and the intensity of staining. Selected cases were also studied for quantitative immunofluorescent staining using the AQUA method.

RESULTS

All 21 cases of SN showed strong and diffuse staining for vimentin; 19 of 21 (91%) cases had an H-score of 300 (average, 294). Similar staining results were observed in SMM; 13 of 14 (93%) cases had an H-score of 300 (average, 297). Muscle-specific actin was weakly and focally positive in 5 of 21 (24%) SN (H-score = 3.3) and 5 of 14 (39%) SMM (H-score = 3.5). The AQUA method showed no significant difference in the staining intensity of SN and SMM for both vimentin and actin.

CONCLUSIONS

There was no difference in the expression of vimentin and actin in SN and SMM shown by conventional immunohistochemistry or the AQUA method. This study shows that MS has much grater sensitivity in detecting the differential expression of these proteins.

MALDI Imaging mass spectrometry: current frontiers and perspectives in pathology research and practice

MALDI Imaging mass spectrometry has entered the field of tissue-based research by providing unique advantages for analyzing tissue specimen in an unprecedented detail. A broad spectrum of analytes ranging from proteins, peptides, protein modification over small molecules, drugs and their metabolites as well as pharmaceutical components, endogenous cell metabolites, lipids, and other analytes are made accessible by this in situ technique in tissue. Some of them were even not accessible in tissues within the histological context before. Thereby, the great advantage of MALDI Imaging is the correlation of molecular information with traditional histology by keeping the spatial localization information of the analytes after mass spectrometric measurement. This method is label-free and allows multiplex analysis of hundreds to thousands of molecules in the very same tissue section simultaneously. Imaging mass spectrometry brings a new quality of molecular data and links the expert discipline of pathology and deep molecular mass spectrometric analysis to tissue-based research. This review will focus on state-of-the-art of MALDI Imaging mass spectrometry, its recent applications by analyzing tissue specimen and the contributions in understanding the biology of disease as well as its perspectives for pathology research and practice.

MALDI TOF imaging mass spectrometry in clinical pathology: a valuable tool for cancer diagnostics (review)

Matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) imaging mass spectrometry (IMS) is an evolving technique in cancer diagnostics and combines the advantages of mass spectrometry (proteomics), detection of numerous molecules, and spatial resolution in histological tissue sections and cytological preparations. This method allows the detection of proteins, peptides, lipids, carbohydrates or glycoconjugates and small molecules.Formalin-fixed paraffin-embedded tissue can also be investigated by IMS, thus, this method seems to be an ideal tool for cancer diagnostics and biomarker discovery. It may add information to the identification of tumor margins and tumor heterogeneity. The technique allows tumor typing, especially identification of the tumor of origin in metastatic tissue, as well as grading and may provide prognostic information. IMS is a valuable method for the identification of biomarkers and can complement histology, immunohistology and molecular pathology in various fields of histopathological diagnostics, especially with regard to identification and grading of tumors.

Hyperspectral imaging of melanocytic lesions

Hyperspectral imaging (HSI) allows the identification of objects through the analysis of their unique spectral signatures. Although first developed many years ago for use in terrestrial remote sensing, this technology has more recently been studied for application in the medical field. With preliminary data favoring a role for HSI in distinguishing normal and lesional skin tissues, we sought to investigate the potential use of HSI as a diagnostic aid in the classification of atypical Spitzoid neoplasms, a group of lesions that often leave dermatopathologists bewildered. One hundred and two hematoxylin and eosin-stained tissue samples were divided into 1 of 4 diagnostic categories (Spitz nevus, Spitz nevus with unusual features, atypical Spitzoid neoplasm, and Spitzoid malignant melanoma) and 1 of 2 control groups (benign melanocytic nevus and malignant melanoma). A region of interest was selected from the dermal component of each sample, thereby maximizing the examination of melanocytes. Tissue samples were examined at ×400 magnification using a spectroscopy system interfaced with a light microscope. The absorbance patterns of wavelengths from 385 to 880 nm were measured and then analyzed within and among groups. All tissue groups demonstrated 3 common absorbance spectra at 496, 533, and 838 nm. Each sample group contained at least one absorption point that was unique to that group. The Spitzoid malignant melanoma category had the highest number of total and unique absorption points for any sample group. The data were then clustered into 12 representative spectral classes. Although each of the sample groups contained all 12 spectral vectors, they did so in differing proportions. These preliminary results reveal differences in the spectral signatures of the Spitzoid lesions examined in this study. Further investigation into a role for HSI in classifying atypical Spitzoid neoplasms is encouraged.

Optimization and comparison of multiple MALDI matrix application methods for small molecule mass spectrometric imaging

The matrix application technique is critical to the success of a matrix-assisted laser desorption/ionization (MALDI) experiment. This work presents a systematic study aiming to evaluate three different matrix application techniques for MALDI mass spectrometric imaging (MSI) of endogenous metabolites from legume plant, Medicago truncatula, root nodules. Airbrush, automatic sprayer, and sublimation matrix application methods were optimized individually for detection of metabolites in the positive ionization mode exploiting the two most widely used MALDI matrices, 2,5-dihydroxybenzoic acid (DHB) and α-cyano-4-hydroxycinnamic acid (CHCA). Analytical reproducibility and analyte diffusion were examined and compared side-by-side for each method. When using DHB, the optimized method developed for the automatic matrix sprayer system resulted in approximately double the number of metabolites detected when compared to sublimation and airbrush. The automatic sprayer method also showed more reproducible results and less analyte diffusion than the airbrush method. Sublimation matrix deposition yielded high spatial resolution and reproducibility but fewer analytes in the higher m/z range (500-1000 m/z). When the samples were placed in a humidity chamber after sublimation, there was enhanced detection of higher mass metabolites but increased analyte diffusion in the lower mass range. When using CHCA, the optimized automatic sprayer method and humidified sublimation method resulted in double the number of metabolites detected compared to standard airbrush method.

Comparative proteomic analysis reveals unique tumor protein composition among the melanoma subtypes pure desmoplastic and superficial spreading

The U.S. death rate for melanoma has not decreased, despite the use of depth at biopsy and sentinel lymph node status to determine the risk of metastasis. Additional prognostic indicators and therapeutic targets are required, and identification of candidate proteins was the goal of this study. We utilized comparative mass spectrometry to compare five samples of each of two forms of melanoma, pure desmoplastic, which by depth at diagnosis has a favorable prognosis, and superficial spreading. Ontological analysis was applied to identify proteins and networks that were increased in one of the two subtypes. Analysis revealed a protein signature increase in pure desmoplastic melanoma associated with cell-to-cell binding and a signature increase in superficial spreading melanoma responsible for the cellular stress response including a constellation of heat shock proteins. The two subtypes of melanoma compared in this study have two unique protein compositions that correlate with their phenotypes. Further validation studies are warranted to evaluate the utility of identified proteins as prognostic markers and therapeutic targets.

Diabetic nephropathy induces alterations in the glomerular and tubule lipid profiles

Diabetic nephropathy (DN) is a major life-threatening complication of diabetes. Renal lesions affect glomeruli and tubules, but the pathogenesis is not completely understood. Phospholipids and glycolipids are molecules that carry out multiple cell functions in health and disease, and their role in DN pathogenesis is unknown. We employed high spatial resolution MALDI imaging MS to determine lipid changes in kidneys of eNOS(-/-) db/db mice, a robust model of DN. Phospholipid and glycolipid structures, localization patterns, and relative tissue levels were determined in individual renal glomeruli and tubules without disturbing tissue morphology. A significant increase in the levels of specific glomerular and tubular lipid species from four different classes, i.e., gangliosides, sulfoglycosphingolipids, lysophospholipids, and phosphatidylethanolamines, was detected in diabetic kidneys compared with nondiabetic controls. Inhibition of nonenzymatic oxidative and glycoxidative pathways attenuated the increase in lipid levels and ameliorated renal pathology, even though blood glucose levels remained unchanged. Our data demonstrate that the levels of specific phospho- and glycolipids in glomeruli and/or tubules are associated with diabetic renal pathology. We suggest that hyperglycemia-induced DN pathogenic mechanisms require intermediate oxidative steps that involve specific phospholipid and glycolipid species.

Imaging mass spectrometry: a new tool for pathology in a molecular age

Mass spectrometry (MS) provides unique advantages for the analysis of clinical specimens, and these capabilities have been critical to the advancement of diagnostic medicine. To date, LC-MS is the MS platform most commonly used for diagnostics; however, LC-MS based proteomics is very labor intensive and costly to implement for high volume assays. Furthermore, when analyzing tissue samples, additional laborious sample preparation steps must be employed (e.g. extraction methods or laser microdissection). The direct analysis of cells and tissues by MALDI imaging MS has developed significant momentum for applications that have diagnostic potential. MALDI imaging MS provides molecular information from specific cell types within tissue sections; however, this laser-based approach significantly reduces the analysis time for each location sampled. This Viewpoint discusses the technologies for direct analysis of tissues, the potential for diagnostic applications using MALDI imaging MS, and the challenges faced in the transfer of the technology to the clinical laboratory.

Clinicopathologic features and survival in Spitzoid malignant melanoma and conventional malignant melanoma

BACKGROUND

Although recent advances in genetics have revealed distinct mutational profiles and molecular signaling pathways associated with Spitzoid malignant melanoma (SMM), less is known about the clinicopathologic characteristics and behavior of SMM compared with conventional melanoma.

OBJECTIVE

We sought to determine the clinicopathologic characteristics and mortality risk associated with SMM and conventional malignant melanoma.

METHODS

We conducted a retrospective study of 30 patients with SMM and 30 patients with conventional melanoma. The two groups were matched by age, gender, and depth of tumor invasion. Additional patient- and tumor-level characteristics were compared between groups and regression modeling was used to assess relative mortality risk.

RESULTS

Unadjusted analyses of SMM and conventional malignant melanoma revealed no significant differences in clinical impression, anatomic location, mitotic rate, and presence of ulceration. Sentinel lymph node biopsy, completion lymphadenectomy, and visceral metastases did not differ between groups. Cox proportional hazards regression showed no differences in mortality between Spitzoid and conventional melanoma.

LIMITATIONS

Small sample size, short follow-up duration, and residual confounding may limit the accuracy and generalizability of our results.

CONCLUSIONS

SMM and conventional malignant melanoma differ in some clinicopathologic features. We did not find a statistically significant difference in mortality between the two.

Imaging mass spectrometry to discriminate breast from pancreatic cancer metastasis in formalin-fixed paraffin-embedded tissues

Diagnosis of the origin of metastasis is mandatory for adequate therapy. In the past, classification of tumors was based on histology (morphological expression of a complex protein pattern), while supportive immunohistochemical investigation relied only on few "tumor specific" proteins. At present, histopathological diagnosis is based on clinical information, morphology, immunohistochemistry, and may include molecular methods. This process is complex, expensive, requires an experienced pathologist and may be time consuming. Currently, proteomic methods have been introduced in various clinical disciplines. MALDI imaging MS combines detection of numerous proteins with morphological features, and seems to be the ideal tool for objective and fast histopathological tumor classification. To study a special tumor type and to identify predictive patterns that could discriminate metastatic breast from pancreatic carcinoma MALDI imaging MS was applied to multitissue paraffin blocks. A statistical classification model was created using a training set of primary carcinoma biopsies. This model was validated on two testing sets of different breast and pancreatic carcinoma specimens. We could discern breast from pancreatic primary tumors with an overall accuracy of 83.38%, a sensitivity of 85.95% and a specificity of 76.96%. Furthermore, breast and pancreatic liver metastases were tested and classified correctly.

Mass spectrometry-based tissue imaging of small molecules

Mass spectrometry imaging (MSI) of tissue samples is a promising analytical tool that has quickly become associated with biomedical and pharmacokinetic studies. It eliminates several labor-intensive protocols associated with more classical imaging techniques and provides accurate histological data at a rapid pace. Because mass spectrometry is used as the readout, MSI can be applied to almost any molecule, especially those that are biologically relevant. Many examples of its utility in the study of peptides and proteins have been reported; here we discuss its value in the mass range of small molecules. We explore its success and potential in the analysis of lipids, medicinals, and metal-based compounds by featuring representative studies from MSI laboratories around the globe.

MSiMass list: a public database of identifications for protein MALDI MS imaging

The clinical application of mass spectrometry imaging has developed into a sizable subdiscipline of proteomics and metabolomics because its seamless integration with pathology enables biomarkers and biomarker profiles to be determined that can aid patient and disease stratification (diagnosis, prognosis, and response to therapy). Confident identification of the discriminating peaks remains a challenge owing to the presence of nontryptic protein fragments, large mass-to-charge ratio ions that are not efficiently fragmented via tandem mass spectrometry or a high density of isobaric species. A public database of identifications has been initiated to aid the clinical development and implementation of mass spectrometry imaging. The MSiMass list database ( www.maldi-msi.org/mass ) enables users to assign identities to the peaks observed in their experiments and provides the methods by which the identifications were obtained. In contrast with existing protein databases, this list is designed as a community effort without a formal review panel. In this concept, authors can freely enter data and can comment on existing entries. In such, the database itself is an experiment on sharing knowledge, and its ability to rapidly provide quality data will be evaluated in the future.

MALDI imaging on large-scale tissue microarrays identifies molecular features associated with tumour phenotype in oesophageal cancer

AIMS

Matrix-assisted laser desorption/ionisation mass spectrometry imaging (MALDI-MSI) and tissue microarray (TMA) technologies were jointly utilized to search for molecular features associated with clinicopathological parameters in oesophageal cancer.

METHODS AND RESULTS

Two TMAs from formalin-fixed tissue samples, including 300 adenocarcinomas and 177 squamous cell carcinomas with clinical follow-up data, were analysed. MALDI-MSI analysis revealed 72 distinct mass per charge (m/z) signals associated with tumour cells, 48 of which were found in squamous cell carcinomas only, and 12 of which were specific for adenocarcinomas. In adenocarcinomas, six signals were linked to early-stage (pT1-T2) tumours (two signals) and the presence (one signal) or absence (three signals) of lymph node metastasis. In squamous cell carcinomas, 24 signals were strongly linked to different phenotypic features, including tumour stage (four signals), histological grade (four signals), and lymph node metastasis (three signals).

CONCLUSIONS

The high number of m/z signals that were found to be significantly linked to one or more phenotypic features of oesophageal cancer highlights the power of MALDI-MSI in the analysis of high-density TMAs. The data also emphasise substantial biological differences between adenocarcinomas and squamous cell carcinomas.

Matrix-assisted laser desorption ionization imaging mass spectrometry: in situ molecular mapping

Matrix-assisted laser desorption ionization imaging mass spectrometry (IMS) is a relatively new imaging modality that allows mapping of a wide range of biomolecules within a thin tissue section. The technology uses a laser beam to directly desorb and ionize molecules from discrete locations on the tissue that are subsequently recorded in a mass spectrometer. IMS is distinguished by the ability to directly measure molecules in situ ranging from small metabolites to proteins, reporting hundreds to thousands of expression patterns from a single imaging experiment. This article reviews recent advances in IMS technology, applications, and experimental strategies that allow it to significantly aid in the discovery and understanding of molecular processes in biological and clinical samples.

Analysis of the formalin-fixed paraffin-embedded tissue proteome: pitfalls, challenges, and future prospectives

Formalin-fixed paraffin-embedded (FFPE) tissues are a real treasure for retrospective analysis considering the amount of samples present in hospital archives, combined with pathological, clinical, and outcome information available for every sample. Although unlocking the proteome of these tissues is still a challenge, new approaches are being developed. In this review, we summarize the different mass spectrometry platforms that are used in human clinical studies to unravel the FFPE proteome. The different ways of extracting crosslinked proteins and the analytical strategies are pointed out. Also, the pitfalls and challenges concerning the quality of FFPE proteomic approaches are depicted. We also evaluated the potential of these analytical methods for future clinical FFPE proteomics applications.

A vision for better health: mass spectrometry imaging for clinical diagnostics

BACKGROUND

Mass spectrometry imaging (MSI) is a powerful tool that grants the ability to investigate a broad mass range of molecules from small molecules to large proteins by creating detailed distribution maps of selected compounds. Its usefulness in biomarker discovery towards clinical applications has obtained success by correlating the molecular expression of tissues acquired from MSI with well-established histology.

RESULTS

To date, MSI has demonstrated its versatility in clinical applications, such as biomarker diagnostics of different diseases, prognostics of disease severities and metabolic response to drug treatment, etc. These studies have provided significant insight in clinical studies over the years and current technical advances are further facilitating the improvement of this field. Although the underlying concept is simple, factors such as choice of ionization method, sample preparation, instrumentation and data analysis must be taken into account for successful applications of MSI. Herein, we briefly reviewed these key elements yet focused on the clinical applications of MSI that cannot be addressed by other means.

CONCLUSIONS

Challenges and future perspectives in this field are also discussed to conclude that the ever-growing applications with continuous development of this powerful analytical tool will lead to a better understanding of the biology of diseases and improvements in clinical diagnostics.

Imaging mass spectrometry in biomarker discovery and validation

Biomarker discovery and validation involves the consideration of many issues and challenges in order to be effectively used for translation from bench to bedside. Imaging mass spectrometry (IMS) is a new technology to assess spatial molecular arrangements in tissue sections, going far beyond microscopy in providing hundreds of different molecular images from a single scan without the need of target-specific reagents. The possibility to correlate distribution maps of multiple analytes with histological and clinical features makes it an ideal tool to discover diagnostic and prognostic markers of diseases. Some recently published studies that show the usefulness and advantages of this technology in the field of cancer research are highlighted.