Genetically heterogeneous and clonally unrelated metastases may arise in patients with cutaneous melanoma

Mapping cancer biology in space: applications and perspectives on spatial omics for oncology

Technologies to decipher cellular biology, such as bulk sequencing technologies and single-cell sequencing technologies, have greatly assisted novel findings in tumor biology. Recent findings in tumor biology suggest that tumors construct architectures that influence the underlying cancerous mechanisms. Increasing research has reported novel techniques to map the tissue in a spatial context or targeted sampling-based characterization and has introduced such technologies to solve oncology regarding tumor heterogeneity, tumor microenvironment, and spatially located biomarkers. In this study, we address spatial technologies that can delineate the omics profile in a spatial context, novel findings discovered via spatial technologies in oncology, and suggest perspectives regarding therapeutic approaches and further technological developments.

Intertumoral Genetic Heterogeneity Generates Distinct Tumor Microenvironments in a Novel Murine Synchronous Melanoma Model

Simple Summary

Metastatic melanoma patients may present with multiple, simultaneous metastases that are genetically different. This intertumoral heterogeneity can cause these tumors to respond differently to the same systemic therapy. Progression of any one tumor, even when others regress, eventually leads to therapy termination. The mechanism underlying these mixed responses remains unknown due to a lack of clinically representative animal models. In a novel murine model of synchronous melanoma that recapitulates human intertumoral heterogeneity, we show that intertumoral genetic heterogeneity leads to the simultaneous generation of distinct tumor immune microenvironments within the same mouse. Furthermore, each tumor can independently regulate local PD-1 (programmed cell death protein 1) and PD-L1 (PD-1 ligand) expressions, an immunosuppressive axis targeted by popular checkpoint immunotherapies. This model is useful for furthering the study of intertumoral heterogeneity and of lesion-specific therapeutic responses.

Abstract

Metastatic melanoma portends a poor prognosis and patients may present with multiple, simultaneous tumors. Despite recent advances in systemic immunotherapy, a majority of patients fail to respond, or exhibit lesion-specific responses wherein some metastases respond as others progress within the same patient. While intertumoral heterogeneity has been clinically associated with these mixed lesion-specific therapeutic responses, no clear mechanism has been identified, largely due to the scarcity of preclinical models. We developed a novel murine synchronous melanoma model that recapitulates this intertumoral genetic and microenvironmental heterogeneity. We show that genetic differences between tumors are sufficient to generate distinct tumor immune microenvironments (TIME) simultaneously in the same mouse. Furthermore, these TIMEs lead to the independent regulation of PD-1/PD-L1 (programmed cell death protein 1/PD-1 ligand), a popular axis targeted by immune checkpoint therapy, in response to ongoing anti-tumor immunity and the presence of interferon-gamma. Currently, therapeutic selection for metastatic melanoma patients is guided by a single biopsy, which may not represent the immune status of all tumors. As a result, patients can display heterogeneous lesion-specific responses. Further investigations into this synchronous melanoma model will provide mechanistic insight into the effects of intertumoral heterogeneity and guide therapeutic selection in this challenging patient population.

Metastatic Melanoma With Features of Desmoplastic Melanoma in a Patient With Primary Cutaneous Superficial Spreading Melanoma With Epithelioid Features

ABSTRACT

The synchronous incidence of 2 different subtypes of melanoma is very rare. Desmoplastic melanoma (DM) can be a diagnostic challenge because of its frequent appearance as a dermal banal spindle cell proliferation. We present a case of a 30-year-old man who developed an irregular, purple, tender plaque measuring 2.5 cm on the right pretibial region. Wide excision of the right leg lesion showed superficial spreading melanoma with epithelioid cells and no spindle cell component. Sentinel lymph node (SLN) biopsy showed an atypical melanocytic proliferation involving one inguinal lymph node with subcapsular and intraparenchymal components. There were spindled tumor cells in lymph node capsule with hyperchromatic nuclei, which were nested within desmoplastic stroma, and were S100- and SOX10-positive and MART1- and HMB-45 negative; in addition to epithelioid tumor cells, which were S100-, SOX10-, and MART1-positive. Multiple discontinuous foci, subcapsular atypical melanocytes, and extracapsular extension helped in excluding capsular nevus. These findings were consistent with DM. Herein, we present an unusual case of primary cutaneous superficial spreading melanoma of the right leg with a predominantly epithelioid morphology that developed metastases to the SLN. The metastasis exhibited divergent differentiation, including both epithelioid morphology identical to the primary, but with additional features of DM that were nonoverlapping with the primary lesion.

Spatially Resolved Transcriptomics Enables Dissection of Genetic Heterogeneity in Stage III Cutaneous Malignant Melanoma

Cutaneous malignant melanoma (melanoma) is characterized by a high mutational load, extensive intertumoral and intratumoral genetic heterogeneity, and complex tumor microenvironment (TME) interactions. Further insights into the mechanisms underlying melanoma are crucial for understanding tumor progression and responses to treatment. Here we adapted the technology of spatial transcriptomics (ST) to melanoma lymph node biopsies and successfully sequenced the transcriptomes of over 2,200 tissue domains. Deconvolution combined with traditional approaches for dimensional reduction of transcriptome-wide data enabled us to both visualize the transcriptional landscape within the tissue and identify gene expression profiles linked to specific histologic entities. Our unsupervised analysis revealed a complex spatial intratumoral composition of melanoma metastases that was not evident through morphologic annotation. Each biopsy showed distinct gene expression profiles and included examples of the coexistence of multiple melanoma signatures within a single tumor region as well as shared profiles for lymphoid tissue characterized according to their spatial location and gene expression profiles. The lymphoid area in close proximity to the tumor region displayed a specific expression pattern, which may reflect the TME, a key component to fully understanding tumor progression. In conclusion, using the ST technology to generate gene expression profiles reveals a detailed landscape of melanoma metastases. This should inspire researchers to integrate spatial information into analyses aiming to identify the factors underlying tumor progression and therapy outcome.Significance: Applying ST technology to gene expression profiling in melanoma lymph node metastases reveals a complex transcriptional landscape in a spatial context, which is essential for understanding the multiple components of tumor progression and therapy outcome. Cancer Res; 78(20); 5970-9. ©2018 AACR.

Multiclonal tumor origin: Evidence and implications

An accurate understanding of the clonal origins of tumors is critical for designing effective strategies to treat or prevent cancer and for guiding the field of cancer risk assessment. The intent of this review is to summarize evidence of multiclonal tumor origin and, thereby, contest the commonly held assumption of monoclonal tumor origin. This review describes relevant studies of X chromosome inactivation, analyses of tumor heterogeneity using other markers, single cell sequencing, and lineage tracing studies in aggregation chimeras and engineered rodent models. Methods for investigating tumor clonality have an inherent bias against detecting multiclonality. Despite this, multiclonality has been observed within all tumor stages and within 53 different types of tumors. For myeloid tumors, monoclonal tumor origin may be the predominant path to cancer and a monoclonal tumor origin cannot be ruled out for a fraction of other cancer types. Nevertheless, a large body of evidence supports the conclusion that most cancers are multiclonal in origin. Cooperation between different cell types and between clones of cells carrying different genetic and/or epigenetic lesions is discussed, along with how polyclonal tumor origin can be integrated with current perspectives on the genesis of tumors. In order to develop biologically sound and useful approaches to cancer risk assessment and precision medicine, mathematical models of carcinogenesis are needed, which incorporate multiclonal tumor origin and the contributions of spontaneous mutations in conjunction with the selective advantages conferred by particular mutations and combinations of mutations. Adherence to the idea that a growth must develop from a single progenitor cell to be considered neoplastic has outlived its usefulness. Moving forward, explicit examination of tumor clonality, using advanced tools, like lineage tracing models, will provide a strong foundation for future advances in clinical oncology and better training for the next generation of oncologists and pathologists.

Prognostic impact and concordance of TERT promoter mutation and protein expression in matched primary and metastatic cutaneous melanoma

Background:

TERT promoter mutations are frequent in melanoma. Here we analysed the concordance and prognostic impact of TERT mutation and telomerase reverse transcriptase (TERT) protein expression in a large melanoma series.

Methods:

In 194 primary nodular melanomas with 72 matched loco-regional metastases, TERT promoter mutation status was assessed by Sanger sequencing and TERT protein expression by immunohistochemistry.

Results:

TERT mutations were found in 68% of primary melanomas and 64% of metastases, and the mutation status was discordant between primary tumour and metastasis in 24% of the cases. 6 of the 10 cases with discordant and wild-type metastases were also TERT wild type when re-tested in other intra-tumour regions, whereas 4 cases were mutation positive. TERT-mutated tumours tended to be thicker, have a higher mitotic count and higher patient age than TERT wild-type cases, but there was no significant association with reduced survival. TERT protein expression did not correlate with mutation status, but showed a similar discordancy between the primary and first metastatic lesion, and was significantly associated with reduced survival.

Conclusions:

TERT promoter mutations showed inter- and intra-tumoural discordancy, whereas only expression of TERT protein was associated with reduced patient survival.

Intratumor and Intertumor Heterogeneity in Melanoma

Melanoma is a cancer that exhibits one of the most aggressive and heterogeneous features. The incidence rate escalates. A high number of clones harboring various mutations contribute to an exceptional level of intratumor heterogeneity of melanoma. It also refers to metastases which may originate from different subclones of primary lesion. Such component of the neoplasm biology is termed intertumor and intratumor heterogeneity. These levels of tumor heterogeneity hinder accurate diagnosis and effective treatment. The increasing number of research on the topic reflects the need for understanding limitation or failure of contemporary therapies. Majority of analyses concentrate on mutations in cancer-related genes. Novel high-throughput techniques reveal even higher degree of variations within a lesion. Consolidation of theories and researches indicates new routes for treatment options such as targets for immunotherapy. The demand for personalized approach in melanoma treatment requires extensive knowledge on intratumor and intertumor heterogeneity on the level of genome, transcriptome/proteome, and epigenome. Thus, achievements in exploration of melanoma variety are described in details. Particularly, the issue of tumor heterogeneity or homogeneity given BRAF mutations is discussed.

Müllerian Adenosarcoma of the Urinary Bladder: Clinicopathologic and Immunohistochemical Features With Novel Genetic Aberrations

BACKGROUND

Müllerian adenosarcoma is a biphasic neoplasm most commonly occurring in the uterus and less frequently of the ovary. It has been rarely described to occur in other sites such as peritoneum and liver.

PATIENTS AND METHODS

In this study, we report the clinicopathologic, immunohistochemical and molecular features of a primary Müllerian adenosarcoma of the urinary bladder in a 62-year-old woman. To our knowledge, this is the first report of detailed pathologic characterization of Müllerian adenosarcoma primary to the urinary bladder in the literature.

RESULTS

Light microscopy showed a biphasic epithelial and stromal tumor with benign-appearing glands surrounded by densely cellular endometrial-type stroma that is densely cellular with increased mitotic figures. The stroma surrounding the glands was more cellular than the intervening areas, which were more loose and edematous. Immunohistochemistry staining revealed positive staining for Pax-2/8 within the glands, for positive CD10 and WT-1 within the spindle cell stroma, and for estrogen and progesterone receptors in both. Staining for desmin, GATA3, p63, and human papillomavirus was negative. Molecular analyses identified mutations in protein kinase B E17K, fms related tyrosine kinase 3 D835N, KRAS proto-oncogene, GTPase G12D, and HRAS proto-oncogene, GTPase G12S. These novel molecular aberrations have yet to be reported in the medical literature. X chromosome inactivation analysis revealed a clonal pattern in the stromal component and a nonclonal pattern in the epithelial component. Currently, the patient is disease/recurrence-free after regular follow-up of approximately 84 months.

CONCLUSION

This case represents, to our knowledge, the first reported diagnosis of Müllerian adenosarcoma arising in the urinary bladder with extensive clinicopathologic, immunohistochemical, and molecular analyses.

In Situ Metabolomics in Cancer by Mass Spectrometry Imaging

Metabolomics is a rapidly evolving and a promising research field with the expectation to improve diagnosis, therapeutic treatment prediction, and prognosis of particular diseases. Among all techniques used to assess the metabolome in biological systems, mass spectrometry imaging is the method of choice to qualitatively and quantitatively analyze metabolite distribution in tissues with a high spatial resolution, thus providing molecular data in relation to cancer histopathology. The technique is ideally suited to study tissues molecular content and is able to provide molecular biomarkers or specific mass signatures which can be used in classification or the prognostic evaluation of tumors. Recently, it was shown that FFPE tissue samples are also suitable for metabolic analyses. This progress in methodology allows access to a highly valuable resource of tissues believed to widen and strengthen metabolic discovery-driven studies.

High Intra- and Inter-Tumoral Heterogeneity of RAS Mutations in Colorectal Cancer

Approximately 30% of patients with wild type RAS metastatic colorectal cancer are non-responders to anti-epidermal growth factor receptor monoclonal antibodies (anti-EGFR mAbs), possibly due to undetected tumoral subclones harboring RAS mutations. The aim of this study was to analyze the distribution of RAS mutations in different areas of the primary tumor, metastatic lymph nodes and distant metastasis. A retrospective cohort of 18 patients with a colorectal cancer (CRC) was included in the study. Multiregion analysis was performed in 60 spatially separated tumor areas according to the pathological tumor node metastasis (pTNM) staging and KRAS, NRAS and BRAF mutations were tested using pyrosequencing. In primary tumors, intra-tumoral heterogeneity for RAS mutation was found in 33% of cases. Inter-tumoral heterogeneity for RAS mutation between primary tumors and metastatic lymph nodes or distant metastasis was found in 36% of cases. Moreover, 28% of tumors had multiple RAS mutated subclones in the same tumor. A high proportion of CRCs presented intra- and/or inter-tumoral heterogeneity, which has relevant clinical implications for anti-EGFR mAbs prescription. These results suggest the need for multiple RAS testing in different parts of the same tumor and/or more sensitive techniques.

Inhibition of the CRAF/prohibitin interaction reverses CRAF-dependent resistance to vemurafenib

Activating BRAF mutations promote constitutive activation of the mitogen-activated protein kinase (MAPK) signaling pathway and are common in a variety of human malignancies, including melanoma and colon cancer. Several small molecule BRAF inhibitors such as vemurafenib have been developed and demonstrate remarkable clinical efficacy. However, resistance typically emerges in most melanoma patients. Studies have demonstrated that reactivation of MAPK signaling via CRAF overexpression and dysregulation is a mechanism for vemurafenib resistance in melanoma. Prohibitins (PHBs) are highly conserved proteins that are thought to control the cell cycle, senescence and tumor suppression. PHB1 is essential for CRAF-mediated ERK1/2 activation through direct binding to CRAF. We developed a CRAF-mediated model of vemurafenib resistance in melanoma cells to assess the importance of the interaction between CRAF and PHB1 in resistance to BRAF-targeting agents. We demonstrate that CRAF overexpression renders melanoma cells resistant to BRAF-targeting agents. Moreover, treatment with the natural compound rocaglamide A disrupts the interaction between PHB and CRAF in melanoma cells, thus reducing MEK1/2 and ERK1/2 signaling, inhibiting melanoma cell growth and inducing apoptosis. The efficacy of these compounds was also demonstrated in a human melanoma xenograft model. Taken together, these data suggest that PHB1 may serve as a novel, druggable target in CRAF-mediated vemurafenib resistance.

Pancreatic cancer metastasis: are we being pre-EMTed?

Pancreatic cancer, often considered a metastatic disease at the time of clinical diagnosis due to lack of any reliable early diagnostic marker(s), is refractory to conventional chemo- and radiotherapy and has a dismal 5-year survival rate of only 6%. Although surgical removal of the primary tumor is considered to be curative, the 5-year survival rate is no more than 20% even in patients with clear resection margins (R0). The recurrence of local and metastatic disease (primarily liver metastasis) post resection is considered to be the leading cause of mortality in these patients. In addition, instances of metastatic disease without any local recurrence post resection have also been observed. Cancer metastasis is the primary cause of mortality in cancer patients and is classically viewed as a late event during the progression of the disease, which is supported by the genetic studies used to understand the evolution of pancreatic cancer. However, this view has recently been challenged by studies using mathematical modeling and genetically labeled mouse models of pancreatic cancer to understand the dynamics of tumor cell dissemination and epithelial to mesenchymal transition (EMT) of tumor cells well before the primary tumor is formed. Given that EMT is a hallmark process that initiates the metastatic seeding of cancer cells and the dismal prognosis of pancreatic cancer patients even after efficient removal of the primary tumor (99.9%), an early dissemination hypothesis of cancer cells cannot be undermined. In this review, we will discuss the current views regarding pancreatic cancer metastasis with particular emphasis on the epithelial to mesenchymal transition, its influence on the selection of patients for surgical resection and the therapeutic intervention.

Discordancy in BRAF mutations among primary and metastatic melanoma lesions: clinical implications for targeted therapy

Systemic targeted molecular therapy, in the form of a selective BRAF inhibitor with or without a MEK inhibitor, is a standard treatment for patients with BRAF V600 mutation-positive melanoma with unresectable stage III and IV disease. Patients with BRAF mutation-negative primary tumors may manifest BRAF mutation-positive metastatic disease. It is unclear whether all metastatic lesions carry the same BRAF mutation status found in the primary tumor and if discordancy exists, in what frequency it occurs. Primary and matched metastatic lesions in 25 melanoma patients were tested for the BRAF V600E/Ec, V600K, V600D, and V600R mutations using a BRAF RGQ PCR kit (Qiagen). Four patients (16%) had discrepancies between their primary and metastatic melanoma BRAF status. Of these patients, 2 (8%) had BRAF mutation-positive primary melanomas with BRAF mutation-negative metastatic lesions and 2 (8%) patient had BRAF mutation-negative melanoma with a BRAF mutation-positive metastatic lesion. In summary, discordancy of BRAF mutation status is not an infrequent finding between primary and metastatic melanoma. It may be prudent in previously negative patients to determine BRAF mutation status of new metastatic tumors for proper allocation of BRAF inhibitor therapy. Discordant BRAF status may have a role in the varying patterns of response and inevitable resistance seen with BRAF inhibitor therapies.

Intratumoral heterogeneity in a Trp53-null mouse model of human breast cancer

Intratumoral heterogeneity correlates with clinical outcome and reflects the cellular complexity and dynamics within a tumor. Such heterogeneity is thought to contribute to radio- and chemoresistance because many treatments may target only certain tumor cell subpopulations. A better understanding of the functional interactions between various subpopulations of cells, therefore, may help in the development of effective cancer treatments. We identified a unique subpopulation of tumor cells expressing mesenchymal-like markers in a Trp53-null mouse model of basal-like breast cancer using fluorescence-activated cell sorting and microarray analysis. Both in vitro and in vivo experiments revealed the existence of cross-talk between these "mesenchymal-like" cells and tumor-initiating cells. Knockdown of genes encoding ligands upregulated in the mesenchymal cells and their corresponding receptors in the tumor-initiating cells resulted in reduced tumorigenicity and increased tumor latency. These studies illustrate the non-cell-autonomous properties and importance of cooperativity between tumor subpopulations.

SIGNIFICANCE

Intratumoral heterogeneity has been considered one important factor in assessing a patient's initial response to treatment and selecting drug regimens to effectively increase tumor response rate. Elucidating the functional interactions between various subpopulations of tumor cells will help provide important new insights in understanding treatment response and tumor progression.

Intra-tumor heterogeneity of BRAF V600E mutation in lung adenocarcinomas

BRAF mutations exist in numerous types of cancer, including melanomas, colorectal cancers and lung cancers. The V600E-specific inhibitor vemurafenib has marked clinical activity in patients with BRAF V600E-mutated melanoma. However, there are many cases of resistance to vemurafenib. This may be due to the reported intra-tumor heterogeneity of the BRAF V600E mutation in primary melanomas. BRAF mutations are found in 1-5% of non-small cell carcinomas (NSCLCs), almost exclusively in adenocarcinoma. A few cases have been reported in which vemurafenib was effective against BRAF V600E-mutated lung cancers. In a previous study, five lung adenocarcinomas with BRAF V600E mutation were detected by direct sequencing. The present study analyzed these tumors for the percentage of mutation (%mutation) by competitive allele-specific polymerase chain reaction (CAST-PCR) assay. In addition, sections of all components of the adenocarcinomas were obtained by laser microdissection and analyzed. The %mutations of BRAF V600E within the macrodissected tumors (cases 1-5) were: Case 1, 10.0%; case 2, 8.0%; case 3, 8.9%; case 4, 21.5%; and case 5, 14.9%. In four cases (cases 2-5), the %mutations of each adenocarcinoma component were as follows: Case 2, lepidic growth 6.5-24.5%, papillary 1.3-11.2% and acinar 9.8%; case 3, solid 2.5-69.9%, acinar 12.4-27.1% and papillary 3.7-17.4%; case 4, acinar 10.0-45.0% and papillary 44.0%; and case 5, papillary 3.7-93.4%. Sensitive BRAF mutation detection methods were used and evidence for heterogeneity of the BRAF V600E mutation in these lung adenocarcinoma cases was observed. Targeted therapy with a BRAF V600E inhibitor such as vemurafenib may have potential in the treatment of lung cancer with this mutation; however, it is necessary to consider how the treatment effect of and drug resistance to BRAF V600E inhibitors are affected by the presence of heterogeneity in future studies.

Comparing BRAF mutation status in matched primary and metastatic cutaneous melanomas: implications on optimized targeted therapy

BACKGROUND

Selective BRAF inhibitors have shown dramatic results with regard to improving outcome in patients with melanoma. Testing the BRAF status in matched primary and metastatic melanomas to optimize individual targeted therapy is not well investigated.

METHODS

Extended BRAF testing using PCR for 9 mutations and VE1 immunohistochemistry for BRAF V600E detection on 95 lesions including 40 primary melanomas with their matched metastases (n = 42), recurrences (n = 9) and second primaries (n = 4) was performed. Nine patients had multiple metastases.

RESULTS

V600E was the only identified mutation type; 35.4% of primary vs. 18.9% of metastatic melanomas. The overall primary-metastatic BRAF status discordance rate was 32.3% using PCR and 27.5% with immunohistochemistry, and was significantly more frequent in primary lesions with mutant BRAF (67%). Males and patients with metastasis to lymph nodes were less likely to be discordant compared to females and those with metastasis to other sites (p = 0.023). Discordant BRAF mutation status was predicted by multivariate binary logistic regression: the presence of a mutant BRAF in the primary melanoma [OR (95% C.I.) = 23.4 (2.4-229.7)] and female gender [OR = 10.6 (1.08-95)]. Inter-metastases BRAF concordance was 100% (6 comparisons).

CONCLUSION

A high discordant rate implies the need for clinical trials addressing the response to targeted therapy in patients with discordant BRAF statuses between their primary and metastatic lesions.

Molecular pathology of malignant melanoma: changing the clinical practice paradigm toward a personalized approach

Melanocytic proliferations are notoriously difficult lesions to evaluate histologically, even among experts, as there is a lack of objective, highly reproducible criteria, which can be broadly applied to the wide range of melanocytic lesions encountered in daily practice. These difficult diagnoses are undeniably further compounded by the substantial medicolegal risks of an "erroneous" diagnosis. Molecular information and classification of melanocytic lesions is already vast and constantly expanding. The application of molecular techniques for the diagnosis of benignity or malignancy is, at times, confusing and limits its utility if not used properly. In addition, current and future therapies will necessitate molecular classification of melanoma into one of several distinct subtypes for appropriate patient-specific therapy. An understanding of what different molecular markers can and cannot predict is of the utmost importance. We discuss both mutational analysis and chromosomal gains/losses to help clarify this continually developing and confusing facet of pathology.

Molecular and genetic diversity in the metastatic process of melanoma

Diversity between metastatic melanoma tumours in individual patients is known; however, the molecular and genetic differences remain unclear. To examine the molecular and genetic differences between metastatic tumours, we performed gene-expression profiling of 63 melanoma tumours obtained from 28 patients (two or three tumours/patient), followed by analysis of their mutational landscape, using targeted deep sequencing of 1697 cancer genes and DNA copy number analysis. Gene-expression signatures revealed discordant phenotypes between tumour lesions within a patient in 50% of the cases. In 18 of 22 patients (where matched normal tissue was available), we found that the multiple lesions within a patient were genetically divergent, with one or more melanoma tumours harbouring 'private' somatic mutations. In one case, the distant subcutaneous metastasis of one patient occurring 3 months after an earlier regional lymph node metastasis had acquired 37 new coding sequence mutations, including mutations in PTEN and CDH1. However, BRAF and NRAS mutations, when present in the first metastasis, were always preserved in subsequent metastases. The patterns of nucleotide substitutions found in this study indicate an influence of UV radiation but possibly also DNA alkylating agents. Our results clearly demonstrate that metastatic melanoma is a molecularly highly heterogeneous disease that continues to progress throughout its clinical course. The private aberrations observed on a background of shared aberrations within a patient provide evidence of continued evolution of individual tumours following divergence from a common parental clone, and might have implications for personalized medicine strategies in melanoma treatment.

Inter- and intra-patient heterogeneity of response and progression to targeted therapy in metastatic melanoma

Background

MAPK inhibitors (MAPKi) are active in BRAF-mutant metastatic melanoma patients, but the extent of response and progression-free survival (PFS) is variable, and complete responses are rare. We sought to examine the patterns of response and progression in patients treated with targeted therapy.

Methods

MAPKi-naïve patients treated with combined dabrafenib and trametinib had all metastases ≥5 mm (lymph nodes ≥15 mm in short axis) visible on computed tomography measured at baseline and throughout treatment.

Results

24 patients had 135 measured metastases (median 4.5/patient, median diameter 16 mm). Time to best response (median 5.5 mo, range 1.7–20.1 mo), and the degree of best response (median −70%, range +9 to −100%) varied amongst patients. 17% of patients achieved complete response (CR), whereas 53% of metastases underwent CR, including 42% ≥10 mm. Metastases that underwent CR were smaller than non-CR metastases (median 11 vs 20 mm, P<0.001). PFS was variable among patients (median 8.2 mo, range 2.6–18.3 mo), and 50% of patients had disease progression in new metastases only. Only 1% (1/71) of CR-metastases subsequently progressed. Twelve-month overall survival was poorer in those with a more heterogeneous initial response to therapy than less heterogeneous (67% vs 93%, P = 0.009).

Conclusion

Melanoma response and progression with MAPKi displays marked inter- and intra-patient heterogeneity. Most metastases undergo complete response, yet only a small proportion of patients achieve an overall complete response. Similarly, disease progression often occurs only in a subset of the tumor burden, and often in new metastases alone. Clinical heterogeneity, likely reflecting molecular heterogeneity, remains a barrier to the effective treatment of melanoma patients.

Concordance of c-kit mutational status in matched primary and metastatic cutaneous canine mast cell tumors at baseline

Background

Mutation analysis of proto‐oncogene c‐kit (c‐kit) is advisable before starting treatment with tyrosine kinase inhibitors in dogs with mast cell tumor (MCT), including those with metastatic disease. Testing is usually performed on primary tumors, assuming that c‐kit mutation status does not change in metastasis.

Hypothesis/Objectives

To give an insight into the mutational processes and to make a recommendation on the use of c‐kit mutational analysis in the clinical setting.

Animals

Twenty‐one client‐owned dogs with metastatic MCT.

Methods

Dogs undergoing resection or biopsy for both primary and matched metastatic MCT were prospectively enrolled. Total RNA or DNA was extracted from primary MCT and corresponding metastases. Exons 8, 9, and 11 were amplified by PCR and sequenced. Genetic features between primary MCT and metastases were compared. Their correlation with clinicopathologic features was investigated.

Results

Concordance (mutated or wild‐type) of mutational status, evaluable in 21 primary and matched metastatic (20 nodal and 1 splenic) MCTs, was 100%. Three new c‐kit mutations were identified. No significant correlation was detected between c‐kit mutation and clinicopathologic features.

Conclusions and Clinical Importance

Proto‐oncogene c‐kit mutational status is conserved between any primary and its matched secondary tumor, suggesting that both can be used for c‐kit mutational testing. Targeted therapies might be also used to treat metastatic disease.

Biological resonance for cancer metastasis, a new hypothesis based on comparisons between primary cancers and metastases

Many hypotheses have been proposed to try to explain cancer metastasis. However, they seem to be contradictory and have some limitations. Comparisons of primary tumors and matched metastases provide new insight into metastasis. The results show high concordances and minor differences at multiple scales from organic level to molecular level. The concordances reflect the commonality between primary cancer and metastasis, and also mean that metastatic cancer cells derived from primary cancer are quite conservative in distant sites. The differences reflect variation that cancer cells must acquire new traits to adapt to foreign milieu during the course of evolving into a new tumor in second organs. These comparisons also provided new information on understanding mechanism of vascular metastasis, organ-specific metastasis, and tumor dormancy. The collective results suggest a new hypothesis, biological resonance (bio-resonance) model. The hypothesis has two aspects. One is that primary cancer and matched metastasis have a common progenitor. The other is that both ancestors of primary cancer cells and metastatic cancer cells are under similar microenvironments and receive similar or same signals. When their interactions reach a status similar to primary cancer, metastasis will occur. Compared with previous hypotheses, the bio-resonance hypothesis seems to be more applicable for cancer metastasis to explain how, when and where metastasis occurs. Thus, it has important implications for individual prediction, prevention and treatment of cancer metastasis.

Low frequency KRAS mutations in colorectal cancer patients and the presence of multiple mutations in oncogenic drivers in non-small cell lung cancer patients

Intratumor heterogeneity can confound the results of mutation analyses in oncodriver genes using traditional methods thereby challenging the application of targeted cancer therapy strategies for patients Ultradeep sequencing can detect low frequency and expanded clonal mutations in primary tumors to better inform treatment decisions. KRAS coding exons in 61 treatment-naive colorectal cancer (CRC) tumors and KRAS, EGFR, ALK, and MET in lung tumors from three Chinese non-small cell lung cancer (NSCLC) patients were sequenced using ultradeep sequencing methods. Forty-one percent of CRC patients (25/61) harbored mutations in the KRAS active domain, eight of which (13%) were not detected by Sanger sequencing. Three (of eight) had frequencies less than 10% and one patient harbored more than one mutation. Low frequency KRAS active (G12R) and EGFR kinase domain mutations (G719A) were identified in one NSCLC patient. A second NSCLC patient showed an EML4-ALK fusion with ALK, EGFR, and MET mutations. A third NSCLC patient harbored multiple low frequency mutations in KRAS, EGFR, and MET as well as ALK gene copy number increases. Within the same patient, multiple low frequency mutations occurred within a gene. A complex pattern of intrinsic low frequency driver mutations in well-known tumor oncogenes may exist prior to treatment, resulting in resistance to targeted therapies. Ultradeep sequencing can characterize intratumor heterogeneity and identify such mutations to ultimately affect treatment decisions.

Towards personalized therapy for patients with malignant melanoma: molecular insights into the biology of BRAF mutations

BRAF mutations have been identified as the most common oncogene mutation in melanomas, especially important in those originating on nonchronically sun-damaged skin. There is a large and continually growing body of evidence regarding the importance of this mutation in targeted therapy for melanoma. In this review, we outline these findings including: molecular pathways used by BRAF, the importance in nonmalignant neoplasms, histologic associations, the relationship of BRAF to KIT and NRAS mutations, and their impact on survival, as well as resistance mechanisms to BRAF inhibitors employed by melanoma. Understanding these topics and how they relate to one another may facilitate the development of new treatments and eventually improve the prognosis for those patients afflicted with this disease.

Biopsies: next-generation biospecimens for tailoring therapy

The majority of samples in existing tumour biobanks are surgical specimens of primary tumours. Insights into tumour biology, such as intratumoural heterogeneity, tumour-host crosstalk, and the evolution of the disease during therapy, require biospecimens from the primary tumour and those that reflect the patient's disease in specific contexts. Next-generation 'omics' technologies facilitate deep interrogation of tumours, but the characteristics of the samples can determine the ultimate accuracy of the results. The challenge is to biopsy tumours, in some cases serially over time, ensuring that the samples are representative, viable, and adequate both in quantity and quality for subsequent molecular applications. The collection of next-generation biospecimens, tumours, and blood samples at defined time points during the disease trajectory--either for discovery research or to guide clinical decisions--presents additional challenges and opportunities. From an organizational perspective, it also requires new additions to the multidisciplinary therapeutic team, notably interventional radiologists, molecular pathologists, and bioinformaticians. In this Review, we describe the existing procedures for sample procurement and processing of next-generation biospecimens, and highlight the issues involved in this endeavour, including the ethical, logistical, scientific, informational, and financial challenges accompanying next-generation biobanking.

Laser-assisted microdissection in translational research: theory, technical considerations, and future applications

Molecular profiling already exerts a profound influence on biomedical research and disease management. Microdissection technologies contribute to the molecular profiling of diseases, enabling investigators to probe genetic characteristics and dissect functional physiology within specific cell populations. Laser-capture microdissection (LCM), in particular, permits collation of genetic, epigenetic, and gene expression differences between normal, premalignant, and malignant cell populations. Its selectivity for specific cell populations promises to greatly improve the diagnosis and management of many human diseases. LCM has been extensively used in cancer research, contributing to the understanding of tumor biology by mutation detection, clonality analysis, epigenetic alteration assessment, gene expression profiling, proteomics, and metabolomics. In this review, we focus on LCM applications for DNA, RNA, and protein analysis in specific cell types and on commercially available LCM platforms. These analyses could clinically be used as aids to cancer diagnosis, clinical management, genomic profile studies, and targeted therapy. In this review, we also discuss the technical details of tissue preparation, analytical yields, tissue selection, and selected applications using LCM.

(18)F-labelled fluorodeoxyglucose-positron emission tomography (FDG-PET) heterogeneity of response is prognostic in dabrafenib treated BRAF mutant metastatic melanoma

BACKGROUND

Little is known about the prevalence and clinical significance of heterogeneity of positron emission tomography with (18)F-labelled fluorodeoxyglucose-positron emission tomography (FDG-PET) response. We aim to determine the prevalence, and clinicopathologic correlates of intra-patient heterogeneity of FDG-PET response in metastatic melanoma treated with dabrafenib, and to determine whether heterogeneity predicts clinical outcome.

METHODS

Patients with BRAF mutant metastatic melanoma and ≥ 2 FDG avid lesions treated on the Phase I trial of dabrafenib at a single institution (n=23) were included. FDG-PET response was assessed by comparing baseline PET scans with scans at day 15. A heterogeneous response was defined as responding and new or metabolically progressing lesion(s) in a patient, or >10% of lesions with a stable metabolic response and responding lesions in a patient.

RESULTS

Six (26%) patients had a heterogeneous PET response. The median time to progression (TTP) was 7.4 months (95% confidence interval (CI): 6.5-8.3) for PET homogeneous responders and 3.0 months (95%CI: 0.6-5.4) for PET heterogeneous responders. There were no homogeneous non-responders. Age, BRAF mutation genotype, dose, and lactate dehydrogenase, did not predict for heterogeneity of PET response. Heterogeneity did not correlate with tumour response. Lung metastases were more likely to respond than other visceral metastatic sites.

CONCLUSIONS

Heterogeneous FDG-PET responses are common in metastatic melanoma treated with dabrafenib, and heterogeneity is associated with a shorter TTP. FDG-PET heterogeneity may predict molecular heterogeneity, and FDG-PET directed biopsies may facilitate investigation into mechanisms of resistance to signal pathway inhibitors.

Differing von hippel lindau genotype in paired primary and metastatic tumors in patients with clear cell renal cell carcinoma

In sporadic clear cell renal cell carcinoma (CCRCC), the von Hippel Lindau (VHL) gene is inactivated by mutation or methylation in the majority of primary (P) tumors. Due to differing effects of wild-type (WT) and mutant (MT) VHL gene on downstream signaling pathways regulating angiogenesis, VHL gene status could impact clinical outcome. In CCRCC, comparative genomic hybridization analysis studies have reported genetic differences between paired P and metastatic (M) tumors. We thus sequenced the VHL gene in paired tumor specimens from 10 patients to determine a possible clonal relationship between the P tumor and M lesion(s) in patients with CCRCC. Using paraffin-embedded specimens, genomic DNA from microdissected samples (>80% tumor) of paired P tumor and M lesions from all 10 patients, as well as in normal tissue from 6 of these cases, was analyzed. The DNA was used for PCR-based amplification of each of the 3 exons of the VHL gene. Sequences derived from amplified samples were compared to the wild-type VHL gene sequence (GenBank Accession No. AF010238). Methylation status of the VHL gene was determined using VHL methylation-specific PCR primers after DNA bisulfite modification. In 4/10 (40%) patients the VHL gene status differed between the P tumor and the M lesion. As expected, when the VHL gene was mutated in both the P tumor and M lesion, the mutation was identical. Further, while the VHL genotype differed between the primary tumor in different kidneys or multiple metastatic lesions in the same patient, the VHL germline genotype in the normal adjacent tissue was always wild-type irrespective of the VHL gene status in the P tumor. These results demonstrate for the first time that the VHL gene status can be different between paired primary and metastatic tissue in patients with CCRCC.

Cancer stem cells in tumor heterogeneity

Cancer cells within a given tumor were long regarded as a largely homogeneous group of cells originating from a common progenitor cell. However, it is increasingly appreciated that there is a considerable heterogeneity within tumors also on the tumor cell level. This heterogeneity extends to virtually all measurable properties of cancer cells, ranging from differentiation state, proliferation rate, migratory and invasive capacity to size, and therapeutic response. Such heterogeneity likely represents a major therapeutic hurdle, but the mechanisms underlying its emergence remain poorly understood and a controversial topic. The cancer stem cell model of tumor progression has gained increasing support during the past several years. In this review, I will discuss some major implications of the cancer stem cell hypothesis on the origins of tumor heterogeneity, focusing both on heterogeneity within the tumor cells proper and on potential transdifferentiation of cancer stem cells into stromal and endothelial lineages, as well as on heterogeneity of the therapeutic response. Evidence for and against a direct and causal role of cancer stem cells in the emergence of tumor heterogeneity will be weighed and alternative explanations for apparently contradictory observations discussed. Finally, I will discuss the potential origins of cancer stem cells and the various implications of origin to the contribution to tumor heterogeneity, and outline some future directions.

Intra- and inter-tumor heterogeneity of BRAF(V600E))mutations in primary and metastatic melanoma

The rationale for using small molecule inhibitors of oncogenic proteins as cancer therapies depends, at least in part, on the assumption that metastatic tumors are primarily clonal with respect to mutant oncogene. With the emergence of BRAF(V600E) as a therapeutic target, we investigated intra- and inter-tumor heterogeneity in melanoma using detection of the BRAF(V600E) mutation as a marker of clonality. BRAF mutant-specific PCR (MS-PCR) and conventional sequencing were performed on 112 tumors from 73 patients, including patients with matched primary and metastatic specimens (n = 18). Nineteen patients had tissues available from multiple metastatic sites. Mutations were detected in 36/112 (32%) melanomas using conventional sequencing, and 85/112 (76%) using MS-PCR. The better sensitivity of the MS-PCR to detect the mutant BRAF(V600E) allele was not due to the presence of contaminating normal tissue, suggesting that the tumor was comprised of subclones of differing BRAF genotypes. To determine if tumor subclones were present in individual primary melanomas, we performed laser microdissection and mutation detection via sequencing and BRAF(V600E)-specific SNaPshot analysis in 9 cases. Six of these cases demonstrated differing proportions of BRAF(V600E)and BRAF(wild-type) cells in distinct microdissected regions within individual tumors. Additional analyses of multiple metastatic samples from individual patients using the highly sensitive MS-PCR without microdissection revealed that 5/19 (26%) patients had metastases that were discordant for the BRAF(V600E) mutation. In conclusion, we used highly sensitive BRAF mutation detection methods and observed substantial evidence for heterogeneity of the BRAF(V600E) mutation within individual melanoma tumor specimens, and among multiple specimens from individual patients. Given the varied clinical responses of patients to BRAF inhibitor therapy, these data suggest that additional studies to determine possible associations between clinical outcomes and intra- and inter-tumor heterogeneity could prove fruitful.

Normal stem cells and cancer stem cells: similar and different

The functional capabilities of normal stem cells and tumorigenic cancer cells are conceptually similar in that both cell types are able to proliferate extensively. Indeed, mechanisms that regulate the defining property of normal stem cells - self-renewal - also frequently mediate oncogenesis. These conceptual links are strengthened by observations in some cancers that tumorigenic cells can not only renew their malignant potential but also generate bulk populations of non-tumorigenic cells in a manner that parallels the development of differentiated progeny from normal stem cells. But cancer cells are not normal. Although tumorigenic cells and normal stem cells are similar in some ways, they are also fundamentally different in other ways. Understanding both shared and distinguishing mechanisms that regulate normal stem cell proliferation and tumor propagation is likely to reveal opportunities for improving the treatment of patients with cancer.

Genetic disparity between primary tumours, disseminated tumour cells, and manifest metastasis

Recent genetic analyses of paired samples from primary tumours and disseminated tumour cells have uncovered a bewildering genetic disparity. It was therefore proposed that ectopically residing tumour cells disseminate early and develop independently into metastases parallel to the primary tumour. Alternatively, these cells may represent an irrelevant cell population unable to spawn metastases whereas only cells that disseminated late in primary tumour development (which therefore are similar to the primary tumour) will form manifest metastasis. Here, we review comparative analyses of paired samples from primary tumours and disseminated tumour cells or primary tumours and metastases. The data demonstrate a striking disparity, questioning the use of primary tumours as surrogate for the genetics of systemic cancer. In the era of molecular therapies that build upon genetic defects of tumour cells, these data call for a direct diagnostic pathology of systemic cancer.

Parallel progression of primary tumours and metastases

Systemic cancer progression is accounted for in two basic models. The prevailing archetype places the engine of cancer progression within the primary tumour before metastatic dissemination of fully malignant cells. The second posits parallel, independent progression of metastases arising from early disseminated tumour cells. This Perspective draws together data from disease courses, tumour growth rates, autopsy studies, clinical trials and molecular genetic analyses of primary and disseminated tumour cells in support of the parallel progression model. Consideration of this model urges review of current diagnostic and therapeutic routines.

Evaluation of the clonal origin of multiple primary melanomas using molecular profiling

Numerous investigations have been conducted using molecular profiling to evaluate the possible clonal origin of second malignancies in various cancer types. However, to date no study assessing clonality of multiple primaries has been conducted in melanoma. In this investigation using patients treated at a specialist melanoma treatment center, we compared the somatic mutational profiles of pairs of melanomas designated as independent on the basis of thorough assessment of their clinical and pathologic characteristics. We used a set of highly polymorphic genetic markers selected on the basis of their chromosomal positions and the frequencies of reported allelic losses at these genetic loci. Our statistical testing strategy showed no significant evidence of clonal origin of the two primaries in 17 of the 19 patients examined. The results suggest that most second melanomas designated as independent primary tumors on the basis of their clinicopathologic features are indeed independent occurrences of the disease, supporting the validity of the criteria used by experienced pathologists in distinguishing new primaries from metastases.

Cell-to-cell fusion as a link between viruses and cancer

The ability to fuse cells is shared by many viruses, including common human pathogens and several endogenous viruses. Here we will discuss how cell fusion can link viruses to cancer, what types of cancers it can affect, how the existence of this link can be tested and how the hypotheses that we propose might affect the search for human oncogenic viruses. In particular, we will focus on the ability of cell fusion that is caused by viruses to induce chromosomal instability, a common affliction of cancer cells that has been thought to underlie the malignant properties of cancerous tumours.

Clonal relationships between epidermotropic metastatic melanomas and their primary lesions: a loss of heterozygosity and X-chromosome inactivation-based analysis

Loss of heterozygosity (LOH) has previously been demonstrated at multiple chromosome microsatellites in primary and metastatic melanomas. Epidermotropic metastases of melanoma are unique in their varied histopathologic appearance, which can mimic a primary lesion. Our objective was to compare LOH profiles in primary and epidermotropic metastatic melanoma to delineate their clonal relationship. We examined the pattern of allelic loss in the primary melanomas of nine patients in addition to the 21 corresponding epidermotropic metastatic melanomas (average 2.3 metastases per patient). DNA samples were prepared from formalin-fixed, paraffin-embedded tissue sections using laser capture microdissection. Eight DNA microsatellite markers on six different chromosomes were analyzed: D1S214 (1p), D6S305 (6q), D9S171 (9p), D9S157 (9p), IFNA (9p), D10S212 (10q), D11S258 (11q), D18S70 (18q). In addition, X-chromosome inactivation analysis was performed in tumors from four women. LOH was seen in 67% (6/9) of primary melanomas and 81% (17/21) of epidermotropic metastatic melanomas. The most frequent allelic losses in informative cases occurred at 10q (33%), 9p (22%), and 11q (22%) in primary melanomas, and at 10q (50%), 1p (44%), and 6q (39%) in epidermotropic metastatic melanomas. Primary lesions demonstrating LOH had concordant allelic loss in at least one locus in a corresponding epidermotropic metastatic melanoma in 83% (5/6) of cases. X-chromosome analysis showed nonrandom inactivation in 75% (3/4) and 71% (5/7) of primary melanoma and epidermotropic metastatic melanoma cases, respectively. Our LOH and X-chromosome inactivation analysis data suggest that epidermotropically metastatic melanomas are clonally related to their primary lesion in many cases. Our data also indicated that some cases diagnosed as epidermotropic metastatic melanoma might be divergent clones or new primaries rather than metastatic disease.