Genetic characterisation of molecular targets in carcinoma of unknown primary

Tumor diagnosis recharacterization enabled by comprehensive genomic profiling to guide precision medicine strategy

Comprehensive genomic profiling (CGP) via next-generation sequencing is standard clinical practice for advanced and metastatic cancers in the U.S. and can help identify clinically actionable alterations in patients who may benefit from targeted therapies. CGP can also complement clinicopathological findings and in certain cases, may lead to diagnostic recharacterization resulting in more precise therapeutic strategies. Here, we highlight examples where molecular findings resulted in tumor re-evaluation and subsequent recharacterization. Twenty-eight cases where CGP results were inconsistent with initial pathological diagnosis and clinical presentation were selected for secondary clinicopathological review to explore alternative diagnostic explanations more consistent with the genomic results. Genomic profiling identified clinically actionable and prognostic variants leading to more accurate therapeutic recommendations based on the updated diagnoses highlighting the value of CGP beyond biomarker detection for therapy selection and supporting its complementary use in diagnostic confirmation to unveil opportunities for precision medicine strategies.

Impact of whole genome sequencing on the care pathway for patients with cancer of unknown primary

BACKGROUND

Patients with metastatic disease and no identifiable primary tumor, thus diagnosed with cancer of unknown primary (CUP), typically have a poor prognosis. Tumor DNA sequencing has recently shown promise in identifying the molecular tissue of origin. This study evaluated the value of whole genome sequencing (WGS) in the CUP care pathway, by comparing patient outcomes with a historical control cohort. Also, the value of whole transcriptome sequencing (WTS) was explored.

PATIENTS AND METHODS

A prospective intervention cohort was established of provisional CUP patients (≥18 years of age) who had WGS carried out on metastatic tissue between August 2021 and August 2023. A control cohort was established of CUP patients (≥18 years of age) diagnosed between December 2016 and April 2021 without the availability of WGS. The CUP predicting algorithm was applied to WGS data, and data on definitive diagnosis, molecular actionable alterations [ESMO Scale for Clinical Actionability of molecular Targets (ESCAT) tier 1-3], therapy, diagnostic timelines, and overall survival (OS) were captured.

RESULTS

A total of 159 provisional CUP patients (n = 54 intervention cohort, n = 105 control cohort) were included. WGS and WTS were successfully carried out in 46 (85%) and 27 patients (50%). A primary tumor diagnosis was established in 76% of the intervention cohort compared with 16% of the control cohort (P < 0.001). WGS contributed to a primary tumor diagnosis in 34 patients (63%) and identified an actionable alteration in 34 patients (63%). WTS contributed to a primary tumor diagnosis in three patients (6%). Following WGS, treatment recommendations could be made for 38 patients (70%), of whom 22 started the recommended therapies (58%). The median OS was 11 and 9 months in the intervention and control cohorts, respectively (P = 0.345).

CONCLUSION

Incorporation of WGS into the CUP care pathway is of significant value for diagnosing a primary tumor of origin and contributed to the identification of actionable alterations in the majority of patients.

When neck lymph nodes metastases do not origin from a head and neck unknown primary

PURPOSE OF REVIEW

The evidence for a standardized approach to the management of cervical metastasis from a distant primary tumour is limited. The objective of this review is to provide an overview of the current status of research in this field and to present the latest diagnostic and therapeutic approaches.

RECENT FINDINGS

Although infraclavicular tumours are typically observed to metastasise to levels IV and V of the neck, all levels may potentially be affected. In conjunction with imaging and immunohistochemical analyses, next-generation sequencing and artificial intelligence-based tools are emerging as potential methods for identifying the primary tumour. Cervical metastasis can be classified as N3 or M1 in accordance with the histology and site of the primary tumour. A neck dissection + adjuvant chemoradiotherapy may prove beneficial in selected patients with breast, nonsmall cell lung, renal cell, oesophageal and testicular cancers, resulting in improved survival rates.

SUMMARY

The diagnosis and subsequent treatment of such cases requires the input of a multidisciplinary team, as the condition is often complex and requires a multifaceted approach. Isolated supraclavicular metastases should prompt the clinician to investigate a distant primary. In select patients with some types of primary tumours, surgical treatment of the neck may improve the prognosis. It is, therefore, essential to control the primary tumour in order to optimize the success of the overall treatment plan.

Synergic activity of FGFR2 and MEK inhibitors in the treatment of FGFR2-amplified cancers of unknown primary

Patients with cancer of unknown primary (CUP) carry the double burden of an aggressive disease and reduced access to therapies. Experimental models are pivotal for CUP biology investigation and drug testing. We derived two CUP cell lines (CUP#55 and #96) and corresponding patient-derived xenografts (PDXs), from ascites tumor cells. CUP cell lines and PDXs underwent histological, immune-phenotypical, molecular, and genomic characterization confirming the features of the original tumor. The tissue-of-origin prediction was obtained from the tumor microRNA expression profile and confirmed by single-cell transcriptomics. Genomic testing and fluorescence in situ hybridization analysis identified FGFR2 gene amplification in both models, in the form of homogeneously staining region (HSR) in CUP#55 and double minutes in CUP#96. FGFR2 was recognized as the main oncogenic driver and therapeutic target. FGFR2-targeting drug BGJ398 (infigratinib) in combination with the MEK inhibitor trametinib proved to be synergic and exceptionally active, both in vitro and in vivo. The effects of the combined treatment by single-cell gene expression analysis revealed a remarkable plasticity of tumor cells and the greater sensitivity of cells with epithelial phenotype. This study brings personalized therapy closer to CUP patients and provides the rationale for FGFR2 and MEK targeting in metastatic tumors with FGFR2 pathway activation.

From pre-clinical to translational brain metastasis research: current challenges and emerging opportunities

Brain metastasis, characterized by poor clinical outcomes, is a devastating disease. Despite significant mechanistic and therapeutic advances in recent years, pivotal improvements in clinical interventions have remained elusive. The heterogeneous nature of the primary tumor of origin, complications in drug delivery across the blood-brain barrier, and the distinct microenvironment collectively pose formidable clinical challenges in developing new treatments for patients with brain metastasis. Although current preclinical models have deepened our basic understanding of the disease, much of the existing research on brain metastasis has employed a reductionist approach. This approach, which often relies on either in vitro systems or in vivo injection models in young and treatment-naive mouse models, does not give sufficient consideration to the clinical context. Given the translational importance of brain metastasis research, we advocate for the design of preclinical experimental models that take into account these unique clinical challenges and align more closely with current clinical practices. We anticipate that aligning and simulating real-world patient conditions will facilitate the development of more translatable treatment regimens. This brief review outlines the most pressing clinical challenges, the current state of research in addressing them, and offers perspectives on innovative metastasis models and tools aimed at identifying novel strategies for more effective management of clinical brain metastasis.

Advances in Cancer Research: Current and Future Diagnostic and Therapeutic Strategies

Cancers of unknown primary (CUP) exhibit significant cellular heterogeneity and malignancy, which poses significant challenges for diagnosis and treatment. Recent years have seen deeper insights into the imaging, pathology, and genetic characteristics of CUP, driven by interdisciplinary collaboration and the evolution of diagnostic and therapeutic strategies. However, due to their insidious onset, lack of evidence-based medicine, and limited clinical understanding, diagnosing and treating CUP remain a significant challenge. To inspire more creative and fantastic research, herein, we report and highlight recent advances in the diagnosis and therapeutic strategies of CUP. Specifically, we discuss advanced diagnostic technologies, including 12-deoxy-2-[fluorine-18]fluoro-D-glucose integrated with computed tomography (18F-FDG PET/CT) or 68Ga-FAPI (fibroblast activation protein inhibitor) PET/CT, liquid biopsy, molecular diagnostics, self-assembling nanotechnology, and artificial intelligence (AI). In particular, the discussion will extend to the effective treatment techniques currently available, such as targeted therapies, immunotherapies, and bio-nanotechnology-based therapeutics. Finally, a novel perspective on the challenges and directions for future CUP diagnostic and therapeutic strategies is discussed.

Clinical features of cancer with unknown primary site (clinical features, treatment, prognosis of cancer with unknown primary site)

Cancer of unknown primary site(CUPs) is a metastatic syndrome with an unidentifiable primary tumor, even after extensive workup to seek the primary site. CUPs accounts for about 3%-5% of the total number of all cancer diagnoses worldwide. The current precision medicine era has reclassified patients with CUPs into the favorable and unfavorable prognostic subset. In this study clinical characteristics and treatment of patients of CUPs were retropactively analysed. Thirty-two patients treated from July 2016 to October 2021 were included in the Affiliated Tumor Hospital of Tianjin Medical University(Tianjin, China).Common symptoms were anemia, fever, enlarged lymph nodes, abdominal pain, edema/multiple serous cavity effusion. Patients with good prognostic factors achieved good outcomes with treatment, conversely, patients with poor prognosis were generally treated empirically and had poorer outcomes. After anti-tumor treatment, the total effective rate was 41 percent(41% was the percentage of patients who achievedtumour respons). To the end of follow-up, after anti-tumor treatment, the median Overall Survival(OS) of patients was 5.4 months.

Refinement of computational identification of somatic copy number alterations using DNA methylation microarrays illustrated in cancers of unknown primary

High-throughput genomic technologies are increasingly used in personalized cancer medicine. However, computational tools to maximize the use of scarce tissues combining distinct molecular layers are needed. Here we present a refined strategy, based on the R-package 'conumee', to better predict somatic copy number alterations (SCNA) from deoxyribonucleic acid (DNA) methylation arrays. Our approach, termed hereafter as 'conumee-KCN', improves SCNA prediction by incorporating tumor purity and dynamic thresholding. We trained our algorithm using paired DNA methylation and SNP Array 6.0 data from The Cancer Genome Atlas samples and confirmed its performance in cancer cell lines. Most importantly, the application of our approach in cancers of unknown primary identified amplified potentially actionable targets that were experimentally validated by Fluorescence in situ hybridization and immunostaining, reaching 100% specificity and 93.3% sensitivity.

Genomic alterations and possible druggable mutations in carcinoma of unknown primary (CUP)

Carcinoma of Unknown Primary (CUP) is a heterogeneous and metastatic disease where the primary site of origin is undetectable. Currently, chemotherapy is the only state-of-art treatment option for CUP patients. The molecular profiling of the tumour, particularly mutation detection, offers a new treatment approach for CUP in a personalized fashion using targeted agents. We analyzed the mutation and copy number alterations profile of 1709 CUP samples deposited in the AACR Project Genomics Evidence Neoplasia Information Exchange (GENIE) cohort and explored potentially druggable mutations. We identified 52 significant mutated genes (SMGs) among CUP samples, in which 13 (25%) of SMGs were potentially targetable with either drugs are approved for the know primary tumour or undergoing clinical trials. The most variants detected were TP53 (43%), KRAS (19.90%), KMT2D (12.60%), and CDKN2A (10.30%). Additionally, using pan-cancer analysis, we found similar variants of TERT promoter in CUP and NSCLC samples, suggesting that these mutations may serve as a diagnostic marker for identifying the primary tumour in CUP. Taken together, the mutation profiling analysis of the CUP tumours may open a new way of identifying druggable targets and consequently administrating appropriate treatment in a personalized manner.

MicroRNA expression profiling with a droplet digital PCR assay enables molecular diagnosis and prognosis of cancers of unknown primary

Metastasis is responsible for the majority of cancer‐related deaths. Particularly, challenging is the management of metastatic cancer of unknown primary site (CUP), whose tissue of origin (TOO) remains undetermined even after extensive investigations and whose therapy is rather unspecific and poorly effective. Molecular approaches to identify the most probable TOO of CUPs can overcome some of these issues. In this study, we applied a predetermined set of 89 microRNAs (miRNAs) to infer the TOO of 53 metastatic cancers of unknown or uncertain origin. The miRNA expression was assessed with droplet digital PCR in 159 samples, including primary tumors from 17 tumor classes (reference set) and metastases of known and unknown origin (test set). We combined two different statistical models for class prediction to obtain the most probable TOOs: the nearest shrunken centroids approach of Prediction Analysis of Microarrays (PAMR) and the least absolute shrinkage and selection operator (LASSO) models. The molecular test was successful for all formalin‐fixed paraffin‐embedded samples and provided a TOO identification within 1 week from the biopsy procedure. The most frequently predicted origins were gastrointestinal, pancreas, breast, lung, and bile duct. The assay was applied also to multiple metastases from the same CUP, collected from different metastatic sites: The predictions showed a strong agreement, intrinsically validating our assay. The final CUPs' TOO prediction was compared with the clinicopathological hypothesis of primary site. Moreover, a panel of 13 miRNAs proved to have prognostic value and be associated with overall survival in CUP patients. Our study demonstrated that miRNA expression profiling in CUP samples could be employed as diagnostic and prognostic test. Our molecular analysis can be performed on request, concomitantly with standard diagnostic workup and in association with genetic profiling, to offer valuable indications about the possible primary site, thereby supporting treatment decisions.

Redefining cancer of unknown primary: Is precision medicine really shifting the paradigm?

The concept of Cancer of Unknown Primary (CUP) has evolved with the advent of medical oncology. CUP can be difficult to diagnose and represents 2 to 5% of new cancers, therefore not exceptionally rare. Within CUPs can be identified a subset of favourable prognosis tumours, however the vast majority of CUP patients belongs to a poor prognosis group. CUP features significant oncological challenges, such as unravelling biological and transversal issues, and most importantly, improving patient's outcomes. In that regard, CUP patients' outcomes regrettably showed minimal improvement for decades and CUP remains a cancer group of very poor prognosis. The biology of CUP has two main hypotheses. One is that CUP is a subgroup of a given primary cancer, where the primary is present but cannot be seen due to its small size. The other, the "true" CUP hypothesis, states that CUP share features that make them a specific entity, whatever their tissue of origin. A true biological signature has not yet been described, but chromosomal instability is a hallmark of poor prognosis CUP group. Precision oncology, despite achieving identifying the putative origin of the CUP, so far failed to globally improve outcomes of patients. Targeting molecular pathways based on molecular analysis in CUP management is under investigation. Immunotherapy has not shown ground-breaking results, to date. Accrual is also a crucial issue in CUP trials. Herein we review CUP history, biological features and remaining questions in CUP biology, the two main approaches of molecular oncology in CUP management, in order to draw perspectives in the enormous challenge of improving CUP patient outcomes.

Cancer of Unknown Primary: Challenges and Progress in Clinical Management

Distant metastases are the main cause of cancer-related deaths in patients with advanced tumors. A standard diagnostic workup usually contains the identification of the tissue-of-origin of metastatic tumors, although under certain circumstances, it remains elusive. This disease setting is defined as cancer of unknown primary (CUP). Accounting for approximately 3-5% of all cancer diagnoses, CUPs are characterized by an aggressive clinical behavior and represent a real therapeutic challenge. The lack of determination of a tissue of origin precludes CUP patients from specific evidence-based therapeutic options or access to clinical trial, which significantly impacts their life expectancy. In the era of precision medicine, it is essential to characterize CUP molecular features, including the expression profile of non-coding RNAs, to improve our understanding of CUP biology and identify novel therapeutic strategies. This review article sheds light on this enigmatic disease by summarizing the current knowledge on CUPs focusing on recent discoveries and emerging diagnostic strategies.

The role of molecular profiling in the diagnosis and management of metastatic undifferentiated cancer of unknown primary✰: Molecular profiling of metastatic cancer of unknown primary

Cancer of unknown primary (CUP) refers to metastatic tumors for which the primary tumor of origin cannot be determined at the time of diagnosis, despite extensive clinicopathologic investigations. Molecular profiling is increasingly able to predict a probable primary tumor type for CUP when clinicopathologic workup is inconclusive. Numerous studies have explored the use of various molecular profiling techniques for identification of site/tissue of origin of CUP. These techniques include gene expression profiling utilizing microarray, reverse transcriptase polymerase chain reaction, RNA-sequencing, somatic gene mutation profiling with next-generation DNA sequencing, and epigenomics including DNA methylation profiling. Despite the generally poor prognosis of CUP, a minority of patients can expect to benefit from targeted therapy despite being agnostic to the tissue of origin. Studies have explored the use of various molecular profiling techniques to predict prognostic and therapeutic biomarkers, with the goal of improving outcome for patients with CUP. However, discordant results between non-randomized and randomized clinical trials in evaluating tumor-type specific therapies raise uncertainties of the benefits of molecularly-predicted tissue of origin-based treatment in routine clinical use. Nevertheless, the current overall trend is in favor of using molecular tools to refine the diagnosis and clinical management of patients with CUP. More large-cohort, randomized prospective studies are needed to assess and validate the utility and feasibility of molecular profiling to uncover potentially targetable genetic alterations. These efforts will also yield further biological insights into the biology and pathogenesis of CUP (Graphical Abstract).

Recommendations for the use of next-generation sequencing (NGS) for patients with metastatic cancers: a report from the ESMO Precision Medicine Working Group

Next-generation sequencing (NGS) allows sequencing of a high number of nucleotides in a short time frame at an affordable cost. While this technology has been widely implemented, there are no recommendations from scientific societies about its use in oncology practice. The European Society for Medical Oncology (ESMO) is proposing three levels of recommendations for the use of NGS. Based on the current evidence, ESMO recommends routine use of NGS on tumour samples in advanced non-squamous non-small-cell lung cancer (NSCLC), prostate cancers, ovarian cancers and cholangiocarcinoma. In these tumours, large multigene panels could be used if they add acceptable extra cost compared with small panels. In colon cancers, NGS could be an alternative to PCR. In addition, based on the KN158 trial and considering that patients with endometrial and small-cell lung cancers should have broad access to anti-programmed cell death 1 (anti-PD1) antibodies, it is recommended to test tumour mutational burden (TMB) in cervical cancers, well- and moderately-differentiated neuroendocrine tumours, salivary cancers, thyroid cancers and vulvar cancers, as TMB-high predicted response to pembrolizumab in these cancers. Outside the indications of multigene panels, and considering that the use of large panels of genes could lead to few clinically meaningful responders, ESMO acknowledges that a patient and a doctor could decide together to order a large panel of genes, pending no extra cost for the public health care system and if the patient is informed about the low likelihood of benefit. ESMO recommends that the use of off-label drugs matched to genomics is done only if an access programme and a procedure of decision has been developed at the national or regional level. Finally, ESMO recommends that clinical research centres develop multigene sequencing as a tool to screen patients eligible for clinical trials and to accelerate drug development, and prospectively capture the data that could further inform how to optimise the use of this technology.

[CUP in the liver]

Hepatic involvement is one of the most common manifestations in cancer of unknown primary (CUP) syndrome. The most frequent secondary neoplasms of the liver are carcinomas and malignant melanomas. Most common carcinoma metastases are adenocarcinomas originating from the digestive system or metastases of breast and lung carcinomas. Therefore, hepatic CUP syndrome is an exclusion diagnosis. Immunohistochemistry and molecular examinations are an important part of histopathological diagnosis. They do not only serve to identify the tissue of histologically origin or possible primary tumor, but also contribute to the selection of a personalized targeted therapy by detecting so-called druggable targets in the interdisciplinary management.

The Quest for Improving Treatment of Cancer of Unknown Primary (CUP) Through Molecularly-Driven Treatments: A Systematic Review

Background: Carcinomas of unknown primary (CUP) account for 3–5% of all malignancy and, despite a reduction in incidence, the overall survival has not improved over the last decade. Chemotherapy regimens have not provided encouraging results. New diagnostic technologies, such as next generation sequencing (NGS), could represent a chance to identify potentially targetable genomic alterations in order to personalize treatment of CUP and provide insights into tumor biology.

Methods: A systematic review of studies of patients with CUP, whose tumor specimen was evaluated through a NGS panel, has been performed on June 10th, 2019 according to PRISMA criteria from PubMed, ASCO meeting library and Clinicaltrial.gov. We have identified potentially targetable alterations for which approved/off-label/in clinical trials drugs are available. Moreover, we have included case reports about CUP patients treated with targeted therapies driven by NGS results in order to explore the clinical role of NGS in this setting.

Results: We have evaluated 15 publications of which eleven studies (9 full-text articles and 2 abstracts) have analyzed the genomic profiling of CUPs through NGS technology, with different platforms and with different patients cohorts, ranging from 16 to 1,806 patients. Among all these studies, 85% of patients demonstrated at least one molecular alteration, the most frequent involving TP53 (41.88%), KRAS (18.81%), CDKN2A (8.8%), and PIK3CA (9.3%). A mean of 47.3% of patients harbored a potentially targetable alteration for which approved/off-label/in clinical trials drugs were available. Furthermore, we have identified 4 case reports in order to evaluate the clinical relevance of a specific targeted therapy identified through NGS.

Conclusions: NGS may represent a tool to improve diagnosis and treatment of CUP by identifying therapeutically actionable alterations and providing insights into tumor biology.

Progress in refining the clinical management of cancer of unknown primary in the molecular era

Cancer of unknown primary (CUP) is an enigmatic disease entity encompassing heterogeneous malignancies without a detectable primary tumour, despite a thorough diagnostic workup. A minority of patients with CUP (15-20%) can be assigned a putative primary tissue of origin according to clinical and histopathological findings and typically have a more favourable prognosis with the use of corresponding tumour type-specific therapies. Thus, the majority of patients with CUP have disease that cannot be assigned to a culprit primary tumour, are treated with empirical chemotherapy and have a poor prognosis. In the molecular era, the use of (epi)genomic or transcriptomic CUP classifiers and DNA or RNA sequencing offers two, sometimes overlapping, therapeutic strategies: tumour type-specific therapy and biomarker-guided therapy. Published data reveal that the accuracy of site-of-origin predictions made using CUP classifiers ranges between 54% and 98% when compared with the assignment made according to the recommended clinicopathological criteria. These advances have led to promising results in non-randomized prospective studies evaluating the efficacy of tumour type-specific therapy; however, the favourable outcomes were not confirmed in randomized controlled studies comparing this approach with standard empirical chemotherapy. Currently, the evidence supporting the use of biomarker-guided therapies is limited to case reports and small case series. In this Review, we discuss the clinical management of CUP in the era of precision medicine. We focus on the advances in understanding the biology of CUP, the implications for the diagnosis and classification of CUP according to the tissue of origin and the shift away from empirical therapy towards tailored therapy.

Integrated clinicomolecular characterization identifies RAS activation and CDKN2A deletion as independent adverse prognostic factors in cancer of unknown primary

Cancer of unknown primary (CUP) denotes a malignancy with histologically confirmed metastatic spread while the primary tumor remains elusive. Here, we address prognostic and therapeutic implications of mutations and copy number variations (CNVs) detected in tumor tissue in the context of a comprehensive clinical risk assessment. Targeted panel sequencing was performed in 252 CUP patients. 71.8% of patients had unfavorable CUP according to ESMO guidelines. 74.7% were adeno- and 13.7% squamous cell carcinomas. DNA was extracted from microdissected formalin-fixed, paraffin-embedded tissues. For library preparation, mostly multiplex PCR-based Ion Torrent AmpliSeq™ technology with Oncomine comprehensive assays was used. Most frequent genetic alterations were mutations/deletions of TP53 (49.6%), CDKN2A (19.0%) and NOTCH1 (14.1%) as well as oncogenic activation of KRAS (23.4%), FGFR4 (14.9%) and PIK3CA (10.7%). KRAS activation was predominantly found in adenocarcinomas (p = 0.01), PIK3CA activation in squamous cell carcinomas (p = 0.03). Male sex, high ECOG score, unfavorable CUP, higher number of involved organs and RAS activation predicted decreased event-free and overall survival in multivariate analysis. Deletions of CDKN2A were prognostically adverse regarding overall survival. TP53 mutations did not significantly influence prognosis in the overall cohort, but worsened prognosis in otherwise favorable CUP subtypes. Although not standard in CUP, for 17/198 (8.6%) patients molecularly targeted treatment was recommended and 10 patients (5.1%) were treated accordingly. In conclusion, besides the identification of drug targets, panel sequencing in CUP is prognostically relevant, with RAS activation and CDKN2A deletion emerging as novel independent risk factors in a comprehensive assessment with clinicopathological data.

Exploring the biological hallmarks of cancer of unknown primary: where do we stand today?

Cancer of unknown primary (CUP) affects a small percentage of the general population. Nonetheless, a substantial number of these patients have a poor prognosis and consequently succumb to their illness within a year of diagnosis. The natural history of CUP is characterised by early metastasis from the unknown primary site, aggressive course and resistance to conventional chemotherapy. Unfortunately, the processes by which this orphan disease originates and progresses have not been fully elucidated and its biology remain unclear. Despite the conceptual progress in genetic and molecular profiling made over the past decade, recognition of the genetic and molecular abnormalities involved in CUP, as well as the identification of the tissue of origin remain unresolved issues. This review will outline the biology of CUP by exploring the hallmarks of cancer in order to rationalise the complexities of this enigmatic syndrome. This approach will help the reader to understand where research efforts currently stand and the pitfalls of this quest.

"Metastatic Cancer of Unknown Primary" or "Primary Metastatic Cancer"?

Cancer of unknown primary (CUP) is an umbrella term used to classify a heterogeneous group of metastatic cancers based on the absence of an identifiable primary tumor. Clinically, CUPs are characterized by a set of distinct features comprising early metastatic dissemination in an atypical pattern, an aggressive clinical course, poor response to empiric chemotherapy and, consequently, a short life expectancy. Two opposing strategies to change the dismal prognosis for the better are pursued. On the one hand, following the traditional tissue-gnostic approach, more and more sophisticated tissue-of-origin (TOO) classifier assays are employed to push identification of the putative primary to its limits with the clear intent of allowing tumor-site specific treatment. However, robust evidence supporting its routine clinical use is still lacking, notably with two recent randomized clinical trials failing to show a patient benefit of TOO-prediction based site-specific treatment over empiric chemotherapy in CUP. On the other hand, with regards to a tissue-agnostic strategy, precision medicine approaches targeting actionable genomic alterations have already transformed the treatment for many known tumor types. Yet, an unmet need remains for well-designed clinical trials to scrutinize its potential role in CUP beyond anecdotal case reports. In the absence of practice changing results, we believe that the emphasis on finding the presumed unknown primary tumor at all costs, implicit in the term CUP, has biased recent research in the field. Focusing on the distinct clinical features shared by all CUPs, we advocate adopting the term primary metastatic cancer (PMC) to denominate a distinct cancer entity instead. In our view, PMC should be considered the archetype of metastatic disease and as such, despite accounting for a mere 2–3% of malignancies, unraveling the mechanisms at play goes beyond improving the prognosis of patients with PMC and promises to greatly enhance our understanding of the metastatic process and carcinogenesis across all cancer types.

Comparative genetic profiling aids diagnosis and clinical decision making in challenging cases of CUP syndrome

Cancer of unknown primary (CUP) denotes cancer cases where metastatic spread is histologically confirmed, but no respective primary tumor can be identified. The challenging diagnosis of CUP is further complicated in cases with previously identified malignancies or with dubious clonal relationship between metastatic sites due to ambiguous histology. Our study aims at elucidating clonal relationships by comparing the respective mutational spectra. Targeted next-generation sequencing (NGS) employing formalin-fixed and paraffin-embedded (FFPE) tumor tissue was performed on 174 consecutive CUP patients. Among these, 43/174 (24.7%) patients had a documented prior malignancy. Data on pairwise targeted NGS testing to address clonal relationships between the previous malignancy and the presumed CUP (n = 11) or between different CUP metastatic sites (n = 7) was available in 18 patients. NGS could clarify clonal relationships in 16/18 cases. Among the 11 CUP patients with antecedent malignancies, four cases were clonally independent of the previous malignancy but harbored deleterious germline mutations in BRCA/BAP1/ATM genes. Seven CUP cases were clonally related to the antecedent malignancy, changing the CUP diagnosis to relapse of the prior malignancy. In the seven CUP cases, with doubtfully related metastatic sites, NGS confirmed clonal relationship in five cases and was inconclusive in two. In conclusion, NGS proved an efficient tool to elucidate clonal relationships in clinically challenging CUP cases. Our study cautions against a premature diagnosis of CUP. Relapses of antecedent malignancies should be carefully considered. CUPs clonally independent from the antecedent malignancy should raise a red flag of a potential cancer-predisposing germline mutation.

Liquid biopsy: a new diagnostic, predictive and prognostic window in cancers of unknown primary

Cancer of unknown primary (CUP) is a heterogeneous group of metastatic cancers characterised by early dissemination of metastases in the absence of any identifiable primary site. Most patients with CUP have poor prognosis with the traditional diagnostic and treatment modalities. Recognising the putative primary tumour is hypothesised to ameliorate the prognosis of patients with CUP by guiding treatment decisions. The active efforts in molecular oncology have shown that gene expression profiling is able to identify the primary tumour site and to determine targetable mutations. In this regard, liquid biopsy opens a new diagnostic, predictive and prognostic window in CUP that may lead to substantial improvement in the management of patients with CUP.