GNAS1 mutations occur more commonly than previously thought in intramuscular myxoma

The prevalence, diagnostic accuracy and genotype-phenotype correlation of GNAS mutations in fibrous dysplasia: a meta-analysis

Background

There is inconsistent evidence regarding the accuracy of GNAS mutations identification for the diagnosis of FD/MAS. This study was performed to estimate the prevalence and diagnostic accuracy of GNAS mutations detection and to preliminarily investigate the genotype-phenotype correlation in FD patients.

Methods

Five electronic databases were searched from 1995 to 2024 using search terms related to GNAS and fibrous dysplasia. Observational studies of FD patients undergoing GNAS mutation detection in FD were included.

Results

A total of 878 FD patients were included. The pooled prevalence of GNAS mutations in FD based on the random effects model was 74% (95% CI = 64%-83%). Regarding diagnostic accuracy, a sensitivity of 0.83 (95% CI, 0.65-0.96), specificity of 0.99 (95% CI, 0.98-1.00) and the area under the receiver operating characteristic curve of 98.38% were found. Additionally, meta-analysis and Fisher's test showed the GNAS mutation types were significantly associated with FD types (OR = 3.51, 95% CI = 1.05 to 11.72; p < 0.05).

Conclusion

A high detection rate of GNAS mutations occurred in FD, and its detection is reliable for diagnosing FD. Additionally, GNAS mutation type was types were significantly associated with FD type.

Systematic Review Registration

Identifier CRD42024553469.

Genetic characterization of intramuscular myxomas

Introduction: Intramuscular myxomas are benign tumors that are challenging to diagnose, especially on core needle biopsies. Acquired chromosomal aberrations and pathogenic variants in codon 201 or codon 227 in GNAS complex locus gene (GNAS) have been reported in these tumors. Here we present our genetic findings in a series of 22 intramuscular myxomas. Materials and methods: The tumors were investigated for the presence of acquired chromosomal aberrations using G-banding and karyotyping. Pathogenic variants in codon 201 or codon 227 of GNAS were assessed using direct cycle Sanger sequencing and Ion AmpliSeq Cancer Hotspot Panel v2 methodologies. Results: Eleven tumors carried chromosomal abnormalities. Six tumors had numerical, four had structural, and one had both numerical and structural chromosomal aberrations. Gains of chromosomes 7 and 8 were the most common abnormalities being found in five and four tumors respectively. Pathogenic variants in GNAS were detected in 19 myxomas (86%) with both methodologies. The detected pathogenic variants were p.R201H in nine cases (seven with abnormal and two with normal karyotypes), p.R201C in five cases, all with normal karyotypes, p.R201S in three cases (two with abnormal and one with normal karyotype), p.R201G in one case with a normal karyotype, and p.Q227E in one case with a normal karyotype. Conclusion: Firstly, our data indicate a possible association between chromosomal abnormalities and GNAS pathogenic variants in intramuscular myxomas. Secondly, the presence of the rare pathogenic variants R201S, p.R201G and p.Q227E in 26% (5 out of 19) of myxomas with GNAS pathogenic variants shows that methodologies designed to detect only the common "hotspot" of p.R201C and p.R201H will give false negative results. Finally, a comparison between Ion AmpliSeq Cancer Hotspot Panel v2 and direct cycle Sanger sequencing showed that direct cycle Sanger sequencing provides a quick, reliable, and relatively cheap method to detect GNAS pathogenic variants, matching even the most cutting-edge sequencing methods.

Molecular testing of soft tissue tumors

BACKGROUND

The diagnosis of soft tissue tumors is challenging, especially when the evaluable material procured is limited. As a result, diagnostic ancillary testing is frequently needed. Moreover, there is a trend in soft tissue pathology toward increasing use of molecular results for tumor classification and prognostication. Hence, diagnosing newer tumor entities such as CIC-rearranged sarcoma explicitly requires molecular testing. Molecular testing can be accomplished by in situ hybridization, polymerase chain reaction, as well as next generation sequencing, and more recently such testing can even be accomplished leveraging an immunohistochemical proxy.

CONCLUSION

This review evaluates the role of different molecular tests in characterizing soft tissue tumors belonging to various cytomorphologic categories that have been sampled by small biopsy and cytologic techniques.

Intramuscular Eyelid Myxoma

Myxomas are a heterogeneous group of mesenchymal tumors. Soft tissue myxomas are divided into myocardial, intramuscular, juxta-articular, superficial, aggressive, and nerve sheath myxomas. Although benign, myxomas have site-specific biologic behavior and syndromic associations, which can influence prognosis and management. In addition, myxomas need to be distinguished from malignant neoplasms, such as myxofibrosarcomas, low-grade fibromyxoid sarcomas, myxoid liposarcomas, and peripheral nerve sheath tumors. While myxomas can occur throughout the body, these tumors arise more commonly in the thigh, shoulder, buttocks, and upper extremity, and less often in the head and neck. Rarely, myxomas can arise in a periocular location, typically in the conjunctiva and eyelid skin. In this case report, we present a patient with recurrent intramuscular myxoma of the eyelid and discuss the differential diagnosis and syndromic associations of this neoplasm. To our knowledge, there have been no prior reports of intramuscular myxoma of the eyelid and orbit.

Extent of Extraskeletal Manifestations of Fibrous Dysplasia/McCune-Albright Syndrome in Patients with Mazabraud's Syndrome

Mazabraud's syndrome (MZB) is a rare condition in which fibrous dysplasia of bone/the McCune-Albright syndrome (FD/MAS) co-exists with intramuscular myxomas. Both FD and the myxomas harbor the GNAS-mutation. Recent studies have shown that extraskeletal, GNAS-related features are associated with a more severe phenotype of FD/MAS. However, patients with MZB are often only seen by orthopedic surgeons. We therefore evaluated MZB patients seen in tertiary referral centers from the Netherlands (LUMC), USA (National Institutes of Health) and France (INSERM UMR 1033 (Lyos), Hôpital Edouard Herriot). All FD/MAS patients known in these centers with an additional diagnosis of a myxoma were included. Demographic information and data on disease extent and extraskeletal manifestations of FD/MAS such as precocious puberty (PP) or café-au-lait patches (CAL) were retrieved from patient's medical records. Thirty MZB patients were included: 20 women (67%) and 10 men (33%). Patients received a diagnosis of MZB (median 42 years, range 16-19) significantly later than the diagnosis of FD/MAS (median 30 years, range 0-60), p < 0.01. Twenty-six patients were diagnosed with polyostotic disease (87%). In 97% the myxoma was located near the skeletal FD lesion. The combination of MZB and MAS was made in 13 patients in whom PP (n = 7), CAL (n = 7), GH-excess (n = 3) and hyperthyroidism (n = 3) were present. Other extraskeletal features were (multinodular) goiter (n = 2) and thyroid cysts (n = 1). Furthermore, in this cohort of patients with MZB several (pre-)malignant tumors were observed; ductal carcinoma in situ of the breast in 3 patients (10%), breast cancer in 1 patient (3.3%), intra pancreatic mucinous neoplasms in 3 patients (10%) and liver adenomas in 2 patients (6.6%). A total of 47% of patients with MZB had an additional extraskeletal feature such as an endocrinopathy. In MZB, 87% of patients suffer from polyostotic FD, 43% of patients have extraskeletal GNAS-features such as an hyperfunctioning endocrinopathy and 30% (pre-)malignant tumors. We therefore advocate that MZB patients should undergo a complete screening and long-term follow-up for extent of bone disease, but also extraskeletal GNAS features of FD/MAS.

Circulating tumour DNA is a promising biomarker for risk stratification of central chondrosarcoma with IDH1/2 and GNAS mutations

Chondrosarcoma (CS) is a rare tumour type and the most common primary malignant bone cancer in adults. The prognosis, currently based on tumour grade, imaging and anatomical location, is not reliable, and more objective biomarkers are required. We aimed to determine whether the level of circulating tumour DNA (ctDNA) in the blood of CS patients could be used to predict outcome. In this multi-institutional study, we recruited 145 patients with cartilaginous tumours, of which 41 were excluded. ctDNA levels were assessed in 83 of the remaining 104 patients, whose tumours harboured a hotspot mutation in IDH1/2 or GNAS. ctDNA was detected pre-operatively in 31/83 (37%) and in 12/31 (39%) patients postoperatively. We found that detection of ctDNA was more accurate than pathology for identification of high-grade tumours and was associated with a poor prognosis; ctDNA was never associated with CS grade 1/atypical cartilaginous tumours (ACT) in the long bones, in neoplasms sited in the small bones of the hands and feet or in tumours measuring less than 80 mm. Although the results are promising, they are based on a small number of patients, and therefore, introduction of this blood test into clinical practice as a complementary assay to current standard-of-care protocols would allow the assay to be assessed more stringently and developed for a more personalised approach for the treatment of patients with CS.

Surgical Treatment of Intramuscular Myxoma

PURPOSE

Intramuscular myxoma (IM) is a rare benign myxoid tumor that may be challenging to differentiate from sarcoma in small amounts of biopsied material. Although IM appears to be well-circumscribed macroscopically, it infiltrates the adjacent edematous muscle microscopically. The recommended treatment is resection, but there is controversy with regard to the appropriate surgical margin. This study aimed to clarify which surgical procedure that should be applied when the preoperative diagnosis is IM and how to manage treatment if the postoperative diagnosis turns out to be a sarcoma.

METHODS

We retrospectively examined 55 IM patients treated from January 1982 to December 2014. Patient characteristics, tumor location, tumor size, radiograph, preoperative and postoperative pathological reports, surgical techniques, treatment outcome, and complications were reviewed. The patients were followed up on for at least 5 years. All patients were confirmed not to have Mazabraud syndrome.

RESULTS

In the 55 IM patients examined, the mean patient age was 48 years and most were female. The most common tumor locations were in the muscles of the thighs (47%) and buttocks (20%). The mean tumor diameter was 5 cm. Wide resection and marginal resection were performed in 24 and 31 patients, respectively. The mean follow-up duration was 19 years. No local recurrence, malignant transformation, or complications were observed.

CONCLUSIONS

Marginal resection is suitable in patients whose preoperative diagnosis is IM, as it is able to prevent local recurrence and allows for the preservation of muscle and muscle fascia. If the postoperative diagnosis turns out to be myxoid sarcoma, minimum surgical contamination makes additional wide resection less invasive.

Pediatric Obturator Internus Muscle Myxoma

Intramuscular myxoma is a rare benign tumor that presents as a slow-growing, deeply seated mass confined within a skeletal muscle. Histologically, these lesions most resemble umbilical cord tissue. They mostly occur in people between 40 and 70 years old, with a 57% female predilection. These tumors are very rare in children. Only one pediatric intramuscular myxoma case is reported in the literature. The goal of this study is to report the case of a 13-year-old girl who presented to our hospital emergency department in 2018 with right hip pain, elevated inflammatory markers, and fever; her initial differential diagnosis was hip septic arthritis, pelvic osteomyelitis, and pelvic abscess. A pelvic MRI revealed a well-defined enhancing round lesion in the right obturator internus muscle. The diagnosis was conformed with a CT-guided core biopsy. The patient's symptoms improved with conservative management, and she continues to be doing well 2 years later. Pediatric pelvic intramuscular myxomas are extremely rare; however, they can have a presentation that mimic a more serious condition such as hip septic arthritis, pelvic osteomyelitis, and pelvic abscess and should be considered in the differential diagnosis in a pediatric patient presenting with hip pain.

Myxoid neoplasms of bone and soft tissue: a pattern-based approach

INTRODUCTION

The accurate diagnosis of musculoskeletal neoplasms is difficult but a pattern-based approach combined with ancillary testing has been shown to improve diagnostic accuracy. The pattern-based approach is particularly appropriate for myxoid lesions.

MATERIALS AND METHODS

The authors reviewed their personal experience of over 3 decades of diagnosing myxoid neoplasms of musculoskeletal lesions.

RESULTS

The authors found that myxoid lesions can be accurately classified based on cell type, nuclear atypia, presence of blood vessel fragments, as well as the results of immunohistochemical and molecular testing.

CONCLUSIONS

Musculoskeletal lesions with a prominence of myxoid or chondroid material in the background can be accurately diagnosed using pattern analysis and ancillary testing.

Oral intramuscular myxoma: case report and brief review of the literature

OBJECTIVE

Myxomas are rare benign mesenchymal soft tissue tumors that seldom affect the head and neck area. The present report describes a rare case of intramuscular myxoma of the oral cavity and briefly reviews the literature regarding the occurrence of these lesions in the maxillofacial area.

STUDY DESIGN

A 59-year-old patient was referred for the development of a slow-growing tumefaction in the right buccal mucosa in the previous 12 months. Magnetic resonance imaging was performed to characterize the lesion's dimensions and its relationship with the surrounding structures, and it revealed intramuscular localization in correspondence with the medial pterygoid muscle. Incisional biopsy was carried out to aid in the final diagnosis.

RESULTS

Histology revealed the presence of an intramuscular myxoma, characterized by discontinuous margins and locally infiltrating muscular fibers. A second surgery was performed to totally remove the lesion. Follow-up at 6 months did not show any signs of recurrence. A literature search was performed to retrieve data on the incidence of oral intramuscular myxomas.

CONCLUSIONS

To the best of our knowledge, this is the first case of intramuscular myxoma of the medial pterygoid muscle reported in the literature. Although rarely encountered, intramuscular myxomas should be considered when performing differential diagnoses of soft tissue masses at the level of the masticatory muscles.

Next generation sequencing for GNAS uncovers CD34 as a sensitive marker for intramuscular myxoma

BACKGROUND

Intramuscular myxoma is a soft tissue myxoid tumor with a broad morphological differential diagnosis and recent developments have led to the identification of markers that can exclude some, but not all, differential diagnostic entities. However, a sensitive confirmatory marker for intramuscular myxoma has not been clearly identified. Since there is some evidence that mutations in the GNAS gene could be such a marker, we evaluated our results of next-generation sequencing testing for GNAS mutations performed in recent years on our series of intramuscular myxoma.

MATERIALS AND METHODS

Next-generation sequencing was performed on 10 cases of intramuscular myxoma diagnosed between 2015 and 2019, using either the TruSight Tumor 26 panel or an in-house developed 97 cancer gene panel. Additionally, immunohistochemistry for CD34 was performed on all cases.

RESULTS

All intramuscular myxomas showed a diffuse and strong expression of CD34 and a GNAS mutation was found in 88% of cases, making this a very sensitive positive test for the diagnosis of intramuscular myxoma.

CONCLUSIONS

Under the condition that contemporary next-generation sequencing is applied as testing method, searching for GNAS mutations is a very sensitive confirmatory test for the diagnosis of intramuscular myxoma, obviating the necessity to perform tests that exclude other entities by the virtue of their negative result. The molecular tests results also identified strong and diffuse CD34 expression as a sensitive, albeit non-specific, marker for intramuscular myxoma.

Correlation of molecular and morphological features of appendiceal epithelial neoplasms

AIMS

The aims of this study were to identify the genetic features of appendiceal epithelial neoplasms and correlate the genetic features with morphology.

METHODS AND RESULTS

We analysed the genetic features of a series of 47 appendiceal epithelial neoplasms of various morphologies by using targeted next-generation sequencing of 11 genes commonly mutated in gastrointestinal neoplasms. Seven of nine serrated polyps harboured BRAF mutations, which are rare in other types of appendiceal tumours. Most cases of low-grade appendiceal mucinous neoplasms (LAMNs) exhibited GNAS and KRAS mutations. LAMNs with a coexisting serrated polyp were all KRAS mutated. Four LAMNs with mutations in the Wnt/β-catenin pathway, either through inactivating mutations in APC or RNF43 or activating mutations in CTNNB1, had focal proliferation of mucin-poor low-grade tumour cells, reminiscent of colorectal adenomas. Mutations in the Wnt/β-catenin pathway were also identified in high-grade appendiceal mucinous neoplasms, suggesting that Wnt/β-catenin pathway activation is the driving force for the progression of LAMN to a higher-grade lesion. Adenomatous polyps of the appendix frequently had APC, KRAS and TP53 mutations and were morphologically and molecularly similar to adenomatous polyps of the colorectum.

CONCLUSIONS

Our results indicate a close association between morphology and genetic events in appendiceal neoplasms and suggest a phylogenetic relationship between different entities.

A case of a myxoma within the obturator externus muscle

Intramuscular myxomas (IM) are rare benign tumors of mesenchymal origin. These tumors have a high myxoid content and a nonspecific radiologic appearance. Here we describe the case of a patient with an IM in an infrequent location; within the obturator externus muscle. A singular approach was utilized for the resection of this tumor in such rare location.

Despite IM being benign tumors, patients may require a surgical excision due to the difficulty of differentiating these tumors, with unreliable imaging features, from other myxoid soft tissue masses.

Identification of novel GNAS mutations in intramuscular myxoma using next-generation sequencing with single-molecule tagged molecular inversion probes

Background

Intramuscular myxoma (IM) is a hypocellular benign soft tissue neoplasm characterized by abundant myxoid stroma and occasional hypercellular areas. These tumors can, especially on biopsy material, be difficult to distinguish from low-grade fibromyxoid sarcoma or low-grade myxofibrosarcoma. GNAS mutations are frequently involved in IM, in contrast to these other malignant tumors. Therefore, sensitive molecular techniques for detection of GNAS aberrations in IM, which frequently yield low amounts of DNA due to poor cellularity, will be beneficial for differential diagnosis.

Methods

In our study, a total of 34 IM samples from 33 patients were analyzed for the presence of GNAS mutations, of which 29 samples were analyzed using a gene-specific TaqMan genotyping assay for the detection of GNAS hotspot mutations c.601C > T and c602G > A in IM, and 32 samples using a novel next generation sequencing (NGS)-based approach employing single-molecule tagged molecular inversion probes (smMIP) to identify mutations in exon 8 and 9 of GNAS. Results between the two assays were compared for their ability to detect GNAS mutations with high confidence.

Results

In total, 23 of 34 samples were successfully analyzed with both techniques showing GNAS mutations in 12 out of 23 (52%) samples. The remaining 11 samples were analyzed with either TaqMan assay or smMIP assay only. The TaqMan assay revealed GNAS mutations in 16 out of 29 samples (55%), with six samples c.601C > T (p.R201C; 38%) and ten samples c.602G > A (p.R201H; 62%) missense mutations. The smMIP assay identified mutations in 16 out of 28 samples (57%), with five samples c.601C > T (p.R201C; 31%) and seven samples c.602G > A (p.R201H; 44%) missense mutations. In addition, four samples (25%) revealed novel IM-associated mutations, including c.601C > A (p.R201S), c.602G > T (p.R201L), c.602G > C (p.R201P) and c.680A > G (p.Q227R). Combining the results of both tests, 23 out of 34 sporadic IM samples (68%) showed a GNAS mutation.

Conclusions

Both the TaqMan and the smMIP assay a show a high degree of concordance in detecting GNAS hotspot mutations in IM with comparable sensitivity. However, since the NGS-based smMIP assay permits mutation detection in whole exons of GNAS, a broader range of GNAS mutations can be identified by the smMIP approach.

Prevalence and Clinical Features of Mazabraud Syndrome: A Multicenter European Study

BACKGROUND

Mazabraud syndrome is a rare disorder, characterized by the presence of fibrous dysplasia (FD) with associated intramuscular myxomas. Data are scarce on the prevalence, clinical features, and natural history of this disorder and outcomes. In this multicenter study, we evaluated a series of patients from 6 European centers.

METHODS

All centers affiliated with the European Musculo-Skeletal Oncology Society (EMSOS) were invited to include data on all patients with Mazabraud syndrome who were seen between 1980 and 2015. The study investigated the prevalence of Mazabraud syndrome, the type, severity, and localization of FD lesions in relation to myxomas, the histopathology of myxomas, and results of GNAS-mutation analysis, when available.

RESULTS

Thirty-two patients (22 female) from 6 centers were included. The prevalence of Mazabraud syndrome was 2.2% in the combined cohort of 1,446 patients with FD, and the syndrome was diagnosed at a mean of 10.1 years after diagnosis of FD. The myxomas were predominantly localized in the upper leg. Excision was performed in 20 patients, recurrence occurred in 6 of these patients (30%) at a median of 8.5 years (range, 1.9 to 16.0 years), and revision surgery was necessary in 5 (25%). High cellularity of myxomas was associated with recurrence (p < 0.05). A GNAS mutation was identified in the myxoma tissue of 5 (83%) of 6 patients with GNAS-mutation analysis.

CONCLUSIONS

This study is the first, to our knowledge, to provide data on the prevalence of Mazabraud syndrome in a relatively large cohort. Although the outcomes of surgical resection were good, a quarter of the patients required revision surgery despite clear resection margins. High cellularity of myxomas was associated with recurrence. GNAS mutations were identified in 83% (5 of 6), emphasizing the shared origin of FD and myxomas. Our data show that patients with FD who have disproportionate complaints, irrespective of FD type, extent, or severity, should be investigated for the possible presence of myxomas.

LEVEL OF EVIDENCE

Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Mutational analysis of high-grade spindle cell sarcoma of the femur in Mazabraud's syndrome

Mazabraud's syndrome is a rare disorder characterised by the association of fibrous dysplasia with intramuscular myxomas. We present a 36-year-old woman with right anterior knee pain and a buttock mass. Imaging showed aggressive bone destruction within an area of fibrous dysplasia in the right femur and a mass with myxoid signal characteristics in the right adductor region. Biopsy of the femur revealed both fibrous dysplasia and a high-grade spindle cell sarcoma. Biopsy of the adductor mass confirmed a soft-tissue myxoma. Molecular genetic analysis revealed an identical R201H substitution in the GNAS1 gene in the sarcoma, the myxoma, and also the conventional fibrous dysplasia.

An update of molecular pathology of bone tumors. Lessons learned from investigating samples by next generation sequencing

The last decade has seen the majority of primary bone tumor subtypes become defined by molecular genetic alteration. Examples include giant cell tumour of bone (H3F3A p.G34W), chondroblastoma (H3F3B p.K36M), mesenchymal chondrosarcoma (HEY1-NCOA2), chondromyxoid fibroma (GRM1 rearrangements), aneurysmal bone cyst (USP6 rearrangements), osteoblastoma/osteoid osteoma (FOS/FOSB rearrangements), and synovial chondromatosis (FN1-ACVR2A and ACVR2A-FN1). All such alterations are mutually exclusive. Many of these have been translated into clinical service using immunohistochemistry or FISH. 60% of central chondrosarcoma is characterised by either isocitrate dehydrogenase (IDH) 1 or IDH2 mutations distinguishing them from other cartilaginous tumours. In contrast, recurrent alterations which are clinically helpful have not been found in high grade osteosarcoma. High throughput next generation sequencing has also proved valuable in identifying germ line alterations in a significant proportion of young patients with primary malignant bone tumors. These findings will play an increasing role in reaching a diagnosis and in patient management.

Applications of Ancillary Testing in the Cytologic Diagnosis of Soft Tissue Neoplasms

Soft tissue neoplasms are diagnostically challenging, although many advances in ancillary testing now enable accurate classification of fine-needle aspiration biopsies by detection of characteristic immunophenotypes (including protein correlates of molecular alterations) and molecular features. Although there are many useful diagnostic immunohistochemical markers and molecular assays, their diagnostic utility relies on correlation with clinical and morphologic features, judicious application, and appropriate interpretation because no single test is perfectly sensitive or specific. This review discusses applications of ancillary testing for commonly encountered soft tissue neoplasms in cytopathologic practice in the context of a pattern-based approach.

Detection of GNAS mutations in intramuscular / cellular myxomas as diagnostic tool in the classification of myxoid soft tissue tumors

BACKGROUND

Intramuscular / cellular myxomas and low-grade myxofibrosarcomas are two different tumor entities with a significant histological overlap, especially if dealing with small biopsies. Despite the morphological similarities, they differ considerably in their biological behaviour. Intramuscular / cellular myxoma rarely shows signs of recurrence and never metastasizes, in contrast to myxofibrosarcoma that tends to recur more aggressively and to metastasize haematologically. Therefore, it is of great importance to distinguish these lesions - evaluation of GNAS mutation status could be of tremendous help.

METHODS

We reviewed 13 cases with intramuscular / cellular myxomas. The 13 cases included 5 men and 8 women, aged from 33 to 71 years (mean age 55.5 years). Immunohistochemistry was performed as well as next generation sequencing. Ten cases were located in the lower extremities and three cases were located in the upper extremities. Two lesions were initially misdiagnosed as a low-grade myxofibrosarcoma.

RESULTS

Performing next generation sequencing 12 out of 13 specimens showed a GNAS mutation.

CONCLUSIONS

Our findings demonstrate that GNAS mutations are more common in intramuscular / cellular myxomas, than had been reported in literature in the past. Next generation sequencing for determining GNAS mutation status on small biopsies or diagnostically challenging cases facilitates the diagnosis of intramuscular / cellular myxoma and separates this tumor entity from its mimics.

The curious case of Gαs gain-of-function in neoplasia

BACKGROUND

Mutations activating the α subunit of heterotrimeric Gs protein are associated with a number of highly specific pathological molecular phenotypes. One of the best characterized is the McCune Albright syndrome. The disease presents with an increased incidence of neoplasias in specific tissues.

MAIN BODY

A similar repertoire of neoplasms can develop whether mutations occur spontaneously in somatic tissues during fetal development or after birth. Glands are the most "permissive" tissues, recently found to include the entire gastrointestinal tract. High frequency of activating Gαs mutations is associated with precise diagnoses (e.g., IPMN, Pyloric gland adenoma, pituitary toxic adenoma). Typically, most neoplastic lesions, from thyroid to pancreas, remain well differentiated but may be a precursor to aggressive cancer.

CONCLUSIONS

Here we propose the possibility that gain-of-function mutations of Gαs interfere with signals in the microenvironment of permissive tissues and lead to a transversal neoplastic phenotype.

COLD-PCR Technologies in the Area of Personalized Medicine: Methodology and Applications

Somatic mutations bear great promise for use as biomarkers for personalized medicine, but are often present only in low abundance in biological material and are therefore difficult to detect. Many assays for mutation analysis in cancer-related genes (hotspots) have been developed to improve diagnosis, prognosis, prediction of drug resistance, and monitoring of the response to treatment. Two major approaches have been developed: mutation-specific amplification methods and methods that enrich and detect mutations without prior knowledge on the exact location and identity of the mutation. CO-amplification at Lower Denaturation temperature Polymerase Chain Reaction (COLD-PCR) methods such as full-, fast-, ice- (improved and complete enrichment), enhanced-ice, and temperature-tolerant COLD-PCR make use of a critical temperature in the polymerase chain reaction to selectively denature wild-type-mutant heteroduplexes, allowing the enrichment of rare mutations. Mutations can subsequently be identified using a variety of laboratory technologies such as high-resolution melting, digital polymerase chain reaction, pyrosequencing, Sanger sequencing, or next-generation sequencing. COLD-PCR methods are sensitive, specific, and accurate if appropriately optimized and have a short time to results. A large variety of clinical samples (tumor DNA, circulating cell-free DNA, circulating cell-free fetal DNA, and circulating tumor cells) have been studied using COLD-PCR in many different applications including the detection of genetic changes in cancer and infectious diseases, non-invasive prenatal diagnosis, detection of microorganisms, or DNA methylation analysis. In this review, we describe in detail the different COLD-PCR approaches, highlighting their specificities, advantages, and inconveniences and demonstrating their use in different fields of biological and biomedical research.

Long-term health outcomes of adults with McCune-Albright syndrome

CONTEXT

McCune-Albright syndrome (MAS) is associated with numerous health problems. Comprehensive long-term health problems of adults with MAS are less well defined in the literature.

OBJECTIVE

Our objective is to report comprehensive health outcomes of adults with MAS (>18 years).

DESIGN

Retrospective case note review of 16 adults with MAS managed by one clinician. Results expressed as median (range).

RESULTS

The study included 16 adults (seven males) with MAS. Median current age is 29 years (20, 46). Twelve of 16 had craniofacial fibrous dysplasia with five of 12 (42%) with progressive facial asymmetry. Growth hormone excess was observed in six of 16 (38%) and T3-toxicosis in five of 16 (31.3%). Six of the seven men (86%) had abnormalities on testicular ultrasound with one man exhibiting marked atrophy of germ and sertoli cells with reduction in spermatogenesis. Six of the 16 (38%) had cardiorespiratory complications including high output cardiac failure (n,3), hypertension (n,2) and one man with congestive cardiac failure and restrictive lung disease. Six of eight (66%) who had screening endoscopy for upper gastrointestinal polyps show increasing numbers of polyps, with benign histology to date. One woman with a previous history of early puberty presented with early aggressive breast carcinoma, which was positive for GNAS. Two patients had GNAS-positive muscle myomas. Platelet dysfunction with bleeding tendency responsive to platelet transfusion during surgery was seen in four.

CONCLUSION

A range of complex health problems is encountered in adults with MAS. These have important implications for transition of patients with MAS and adult care. Long-term cancer risk is currently unknown but requires careful follow-up.

Post-biopsy MRI changes in the size and enhancement of intramuscular myxomas: A report of two cases

Intramuscular myxomas are benign soft-tissue tumors, characterized by bland spindle-shaped cells and fibroblasts within an abundant mucoid matrix on histologic examination. Classically, these are slowly enlarging masses which may occasionally cause pain, paresthesia, and muscle weakness secondary to mass effect. We present an interesting phenomenon of two histologically confirmed cases of intramuscular myxomas that exhibited size and enhancement changes on follow-up imaging after image-guided biopsy. To our knowledge, this is the first report to describe size and enhancement changes of intramuscular myxomas after biopsy.

Karyotyping and analysis of GNAS locus in intramuscular myxomas

Intramuscular myxoma is a benign soft tissue tumor about which very limited genetic information exists. We studied 68 intramuscular myxomas by means of chromosome banding analysis finding abnormal karyotypes in 21 of them. The most clearly nonrandom involvement was of chromosome 8 which was found gained in seven tumors (+8 was the sole change in five myxomas) and structurally rearranged in another two. Since mutation of the gene GNAS (20q13) has been implicated in the pathogenesis of both solitary and hereditary multiple myxomas, we assessed the transcription and mutation status of this gene in five tumors from which we had suitable RNA. All five intramuscular myxomas expressed biallelic transcripts. The mutated GNAS allele found in one tumor was also biallelically transcribed. In none of the five myxomas were maternally expressed transcripts detected. Collectively, the data suggest that intramuscular myxomas have acquired genetic abnormalities that often include chromosome 8 changes but may also involve alterations of GNAS. To what extent these aberrations are pathogenetically important, remains uncertain.

Digital PCR analysis of circulating tumor DNA: a biomarker for chondrosarcoma diagnosis, prognostication, and residual disease detection

Conventional chondrosarcoma is the most common primary bone tumor in adults. Prognosis corresponds with tumor grade but remains variable, especially for individuals with grade (G) II disease. There are currently no biomarkers available for monitoring or prognostication of chondrosarcoma. Circulating tumor DNA (ctDNA) has recently emerged as a promising biomarker for a broad range of tumor types. To date, little has been done to study the presence of ctDNA and its potential utility in the management of sarcomas, including chondrosarcoma. In this study, we have assessed ctDNA levels in a cohort of 71 patients, 32 with sarcoma, including 29 individuals with central chondrosarcoma (CS) and 39 with locally aggressive and benign bone and soft tissue tumors, using digital PCR. In patients with CS, ctDNA was detected in pretreatment samples in 14/29 patients, which showed clear correlation with tumor grade as demonstrated by the detection of ctDNA in all patients with GIII and dedifferentiated disease (n = 6) and in 8/17 patients with GII disease, but never associated with GI CS. Notably detection of ctDNA preoperatively in GII disease was associated with a poor outcome. A total of 14 patients with CS had ctDNA levels assessed at multiple time points and in most patients there was a clear reduction following surgical removal. This research lays the foundation for larger studies to assess the utility of ctDNA for chondrosarcoma diagnosis, prognostication, early detection of residual disease and monitoring disease progression.

Frequency of GNAS R201H substitution mutation in polyostotic fibrous dysplasia: Pyrosequencing analysis in tissue samples with or without decalcification

Guanine nucleotide-binding protein/α-subunit (GNAS) mutations are involved in fibrous dysplasia (FD) pathogenesis. Here, we analyzed GNAS mutations in FD which were performed by pyrosequencing DNA isolated from formalin-fixed paraffin-embedded (FFPE) tissue. The mutation detection rate was determined in FD specimens with and without decalcification. GNAS mutation was identified in 28 cases out of 87 FDs (32.18%) [p.R201C (N = 14) and p.R201H (N = 14)]. GNAS mutation was more likely to occur in polyostotic FD (7/28, 25.0%); FD without GNAS mutation was mostly monostotic form (56/59, 94.9%, P = 0.011). The G > A (R201H) mutation was more frequent in polyostotic FD (6/14 patients, 42.9%) than the C > T (R201C) mutation (1/14, 7.1%) (P = 0.077). We divided the FD cases into two subgroups: tissue specimens that were not decalcified (N = 35, 40.2%), and tissue specimens that were decalcified (N = 52, 59.8%). GNAS mutation was more frequently identified in FD specimens that were not subjected to decalcification (23/35, 65.7%) than in FD specimens that were decalcified (5/52, 9.6%) (P = 0.001). In conclusion, mutation analysis of GNAS by pyrosequencing has diagnostic value in FFPE tissue of patients with FD, especially in specimens that were not decalcified. The R201H substitution mutation of GNAS may be involved in the pathogenesis of polyostotic FD.

An Interesting Case of Intramuscular Myxoma with Scapular Bone Lysis

Introduction. Intramuscular myxoma is a rare benign primitive tumor of the mesenchyme founded at the skeletal muscle level; it presents itself like an unpainful, slow-growing mass. Myxomas with bone lysis are even more rare; only 7 cases have been reported in the English literature, but never at the shoulder level. Case Presentation. We describe an 83-year-old patient with a growing mass in the deltoid muscle with unique scapular lysis, without any symptom. Magnetic resonance imaging (MRI) and a biopsy were performed and the diagnosis of intramuscular myxoma has been retained. In front of this diagnosis of nonmalignant lesion, the decision of a simple follow-up was taken. One year after this decision, the patient was still asymptomatic. Conclusion. In the presence of an intramuscular growing mass with associated bone lysis, intramuscular myxoma as well as malignant tumor should be evoked. MRI has to be part of the initial radiologic appraisal but biopsy is essential to confirm the diagnosis. By consensus, the standard treatment is surgical excision but conservative treatment with simple follow-up can be an option.

Claudin 6 expression is useful to distinguish myxofibrosarcomas from other myxoid soft tissue tumors

Myxofibrosarcoma (MFS) is characterized by abundant myxoid stroma, a wide spectrum of cytological atypia, and frequent local recurrence. Some soft tissue tumors with myxoid stroma can histologically mimic MFS, but have different biological behaviors. Here we sought to identify a useful diagnostic marker for MFS. After our analysis of the gene expression dataset from the Gene Expression Omnibus database, we focused on claudin 6 (CLDN 6). The status of CLDN 6 was assessed by immunohistochemistry in 61 samples of MFS and other (benign) myxoid soft tissue tumors (28 myxoma samples, 12 nodular fasciitis samples), 18 low-grade fibromyxoid sarcoma, 30 myxoid liposarcoma, 29 extraskeletal myxoid chondrosarcoma and 27 dedifferentiated liposarcoma with myxoid feature samples. The correlation between the expression of CLDN 6 and clinicopathological findings in MFS was also investigated. Immunohistochemically, high expression of CLDN 6 was observed in approx. 65% of the MFSs, whereas the benign soft tissue tumors did not show a high expression of CLDN 6. The expression of CLDN 6 in the MFS was significantly higher than those of other tumor specimens. Among the MFSs, the high expression of CLDN 6 was correlated with high FNCLCC grades and high AJCC stages. CLDN 6 may be useful for the differential diagnosis from benign myxoid tumor and for predicting the aggressive biological behavior of MFS.

Novel Association of Odontogenic Myxoma with Constitutional Chromosomal 1q21 Microduplication: Case Report and Review of the Literature

Odontogenic myxoma (OM) is a rare, benign, and locally aggressive tumor. It tends to occur in the posterior maxilla and mandible and is often associated with root resorption and perforation of cortex. Histopathologically, there is a proliferation of spindle, bipolar, and stellate cells, with bland nuclei within a myxoid to infrequently fibromyxoid extracellular matrix. Long, thin residual bony trabeculae are often seen floating within the spindle cell proliferation because of the infiltrating nature of this tumor, and these trabeculae impart a "soap bubble" or "tennis-racket" radiologic appearance. No syndromic association of OM has been reported. Although similar histopathologic features are shared with cardiac myxoma and soft tissue myxoma, mutations in the GNAS gene have not been identified in OM to date, and only 2 of 17 OMs showed mutations in the PRKAR1A gene. In this report, we describe a case of OM in a patient with constitutional 1q21 microduplication, a locus that harbors genes encoding certain proteins in the cAMP-dependent protein kinase A (PKA) signaling pathway, including G-protein-coupled receptors and 1 phosphodiesterase interacting protein. Review of the literature describes the key clinical features and molecular pathogenesis of 1q21 microduplication, as well as highlighting the role of PKA signaling pathway in the pathogenesis of myxomas in general.

Benign soft tissue lesions that may mimic malignancy

Soft tissue lesions which mimic malignancy (pseudosarcomas), represent a significant diagnostic challenge for pathologists. Many features often associated with malignancy including rapid and infiltrative growth, increased cellularity and mitotic activity, and nuclear pleomorphism are present in benign and reactive conditions. This review highlights repair reactions including nodular fasciitis, proliferative fasciitis/myositis, intravascular papillary endothelial hyperplasia, and fat necrosis; lipoma and spindle cell/pleomorphic lipoma; fibroepithelial stromal (pseudosarcomatoid) polyp; phosphaturic mesenchymal tumor; and myxoma. While not inclusive of every pseudoneoplastic soft tissue lesion, this review emphasizes important diagnostic pitfalls and stresses the value of clinical, pathologic, and radiologic correlation.

GNAS(R201H) and Kras(G12D) cooperate to promote murine pancreatic tumorigenesis recapitulating human intraductal papillary mucinous neoplasm

Intraductal papillary mucinous neoplasm (IPMN), the most common pancreatic cystic neoplasm, is known to progress to invasive ductal adenocarcinoma. IPMNs commonly harbor activating somatic mutations in GNAS and KRAS, primarily GNAS(R201H) and KRAS(G12D). GNAS encodes the stimulatory G-protein α subunit (Gsα) that mediates a stimulatory signal to adenylyl cyclase to produce cyclic adenosine monophosphate (cAMP), subsequently activating cAMP-dependent protein kinase A. The GNAS(R201H) mutation results in constitutive activation of Gsα. To study the potential role of GNAS in pancreatic tumorigenesis in vivo, we generated lines of transgenic mice in which the transgene consisted of Lox-STOP-Lox (LSL)-GNAS(R201H) under the control of the CAG promoter (Tg(CAG-LSL-GNAS)). These mice were crossed with pancreatic transcription factor 1a (Ptf1a)-Cre mice (Ptf1a(Cre/+)), generating Tg(CAG-LSL-GNAS);Ptf1a(Cre/+) mice. This mouse line showed elevated cAMP levels, small dilated tubular complex formation, loss of acinar cells and fibrosis in the pancreas; however, no macroscopic tumorigenesis was apparent by 2 months of age. We then crossed Tg(CAG-LSL-GNAS);Ptf1a(Cre/+) mice with LSL-Kras(G12D) mice, generating Tg(CAG-LSL-GNAS);LSL-Kras(G12D);Ptf1a(Cre/+) mice. We used these mice to investigate a possible cooperative effect of GNAS(R201H) and Kras(G12D) in pancreatic tumorigenesis. Within 5 weeks, Tg(CAG-LSL-GNAS);LSL-Kras(G12D);Ptf1a(Cre/+) mice developed a cystic tumor consisting of marked dilated ducts lined with papillary dysplastic epithelia in the pancreas, which closely mimicked the human IPMN. Our data strongly suggest that activating mutations in GNAS and Kras cooperatively promote murine pancreatic tumorigenesis, which recapitulates IPMN. Our mouse model may serve as a unique in vivo platform to find biomarkers and effective drugs for diseases associated with GNAS mutations.

Cell cycle and apoptosis regulatory proteins, proliferative markers, cell signaling molecules, CD209, and decorin immunoreactivity in low-grade myxofibrosarcoma and myxoma

The histologic differential diagnosis between intramuscular myxoma and low-grade myxofibrosarcoma can be quite difficult in some cases. To identify a diagnostic immunohistochemical marker, we compared the staining profiles of 19 different antigens, including cell cycle proteins, apoptosis proteins, and proliferative markers, and selected other signaling and structural proteins in these two tumors. Ten cases each of intramuscular myxoma and low-grade myxofibrosarcoma were stained with antibodies directed against apoptosis regulatory proteins (Bcl2, activated caspase-3, phospho-H2A.X, and cleaved PARP), cell cycle regulatory proteins (Rb1, Cyclin-A, CDKN1B, and Cdt1), proliferative markers (KI67, MCM2, phospho-histone H3, and geminin), cell signalling molecules (c-Myc, EGF, EGFR, PLA2G4A, and HSP90), a dendritic cell marker (CD209), and the extracellular matrix proteoglycan decorin. Staining patterns of myxoma and myxofibrosarcoma were compared using Fisher's exact test and the Mann-Whitney test. For each potential diagnostic marker studied, the proportions of cases scored as positive on both dichotomous or ordinal scales were not significantly different between myxoma and myxofibrosarcoma. Myxoma and myxofibrosarcoma share a common immunophenotype for each of the markers studied. Distinction between these tumors is still predominantly based on morphologic criteria.

GNAS mutation is a frequent event in pancreatic intraductal papillary mucinous neoplasms and associated adenocarcinomas

In contrast to pancreatic ductal adenocarcinomas (PDAs), intraductal papillary mucinous neoplasms (IPMNs) frequently harbour GNAS mutations. To characterise GNAS-mutated pancreatic carcinomas, we examined mutations of GNAS and KRAS in 290 pancreatic adenocarcinomas and 77 pancreatic intraepithelial neoplasias (PanINs). In 64 % (39/61) of IPMNs and 37 % (11/30) of IPMN-associated adenocarcinomas, a GNAS mutation was found. GNAS mutations were frequent (78 %, 7/9) in mucinous carcinomas, with or without associated IPMN. In contrast, GNAS mutations were rarely observed in PDAs (1 %, 1/88) and PanINs (3 %, 2/77), and not at all in mucinous cystic neoplasms (MCNs) (0/10), neuroendocrine neoplasms (0/52), acinar cell neoplasms (0/16), serous cystadenomas (0/10), and solid-pseudopapillary neoplasms (0/14). We found GNAS mutations in 55/91 IPMNs with or without associated invasive carcinoma, solely in intestinal-type (78 %, 21/27) and gastric-type (62 %, 34/55) IPMNs. Of the IPMN-associated adenocarcinomas, mucinous-subtype tumours harboured GNAS mutations more frequently (83 %, 5/6) than tubular-subtype tumours (25 %, 6/24) (p = 0.02). We separately analysed GNAS in the adenocarcinoma and the IPMN component in the IPMN-associated adenocarcinomas. In all mucinous-subtype tumours, the two components exhibited identical genotypes. In contrast, the two components in 8 of 24 tubular-subtype tumours exhibited different genotypes, indicating intratumour heterogeneity. In conclusion, mucinous carcinomas with or without associated IPMN as well as IPMNs frequently harbour a GNAS mutation, reinforcing the notion that these constitute a spectrum of pancreatic tumours. Clinically and pathologically, these tumours are associated, but GNAS mutation sheds further light on this spectrum.

Enhanced ratio of signals enables digital mutation scanning for rare allele detection

The use of droplet digital PCR (ddPCR) for low-level DNA mutation detection in cancer, prenatal diagnosis, and infectious diseases is growing rapidly. However, although ddPCR has been implemented successfully for detection of rare mutations at pre-determined positions, no ddPCR adaptation for mutation scanning exists. Yet, frequently, clinically relevant mutations reside on multiple sequence positions in tumor suppressor genes or complex hotspot mutations in oncogenes. Here, we describe a combination of coamplification at lower denaturation temperature PCR (COLD-PCR) with ddPCR that enables digital mutation scanning within approximately 50-bp sections of a target amplicon. Two FAM/HEX-labeled hydrolysis probes matching the wild-type sequence are used during ddPCR. The ratio of FAM/HEX-positive droplets is constant when wild-type amplicons are amplified but deviates when mutations anywhere under the FAM or HEX probes are present. To enhance the change in FAM/HEX ratio, we employed COLD-PCR cycling conditions that enrich mutation-containing amplicons anywhere on the sequence. We validated COLD-ddPCR on multiple mutations in TP53 and in EGFR using serial mutation dilutions and cell-free circulating DNA samples, and demonstrate detection down to approximately 0.2% to 1.2% mutation abundance. COLD-ddPCR enables a simple, rapid, and robust two-fluorophore detection method for the identification of multiple mutations during ddPCR and potentially can identify unknown DNA variants present in the target sequence.

[Myxoid tumors of deep soft tissues]

Myxoid soft tissue tumors form a heterogeneous group. Their biological potential encompasses the whole spectrum from benign to highly malignant. The present article focuses on myxoid tumors of the deep soft tissues: myxofibrosarcoma, low-grade fibromyxoid sarcoma, myxoma, myxoid liposarcoma, extraskeletal myxoid chondrosarcoma and nodular fasciitis. The last two decades have brought into practice multiple powerful tools that support pathologists in making precise diagnoses, even on small incisional biopsies: detection of fusion transcripts by rt-PCR, detection of chromosomal fusion or breakpoint by FISH, detection of point mutations by PCR and expression of specific markers by immunohistochemistry. Conventional morphology remains the mainstay of diagnosis, and it is essential to obtain adequate clinical and radiological information before interpreting small incisional biopsies. The present article is a summary of morphologic features used to diagnose the most common tumors of the deep soft tissues.

Molecular and genetic aspects of odontogenic lesions

In this article we outline the molecular findings of select odontogenic tumors. In each section, we briefly review selected the clinicoradiographic, histologic, immunologic features, focusing on the molecular findings and their applications in practice. The understanding of molecular pathobiology at various other organ sites has developed quite rapidly in recent years, however much remains unknown about the genetic profile of odontogenic tumors. Improved understanding of mutations in odontogenic tumors may clarify classification schema and elucidate targets for novel therapies. Molecular testing will no doubt improve our understanding of odontogenic tumor pathogenesis and will likely be, someday, an important component of routine clinical practice and its role will only increase in the coming years.

GNAS is frequently mutated in both low-grade and high-grade disseminated appendiceal mucinous neoplasms but does not affect survival

We analyzed a series of 55 disseminated appendiceal mucinous neoplasms treated at our institution for GNAS and KRAS mutations in an attempt to correlate mutation status with clinicopathological findings and patient survival. GNAS mutations (p.R201H, c.602G>A and p.R201C, and c.602C>T) were identified in 17 (31%) of 55 of disseminated mucinous neoplasms and were found in 8 (35%) of 23 low-grade mucinous neoplasms, 7 (37%) of 19 high-grade mucinous adenocarcinomas lacking a signet ring cell component, and 2 (15%) of 13 high-grade mucinous adenocarcinomas with a signet ring cell component. All 7 mucinous adenocarcinomas composed of pure (>95%) signet ring cells harbored wild-type GNAS. There was no significant association between GNAS mutations and sex and age (both with P > .05) or between GNAS mutations and individual adverse histologic features including cytologic grade, destructive invasion, tumor cellularity, angiolymphatic invasion, perineural invasion, and signet ring cells (all with P > .05). KRAS mutations were identified in 22 (40%) of 55 disseminated mucinous neoplasms. GNAS-mutated disseminated appendiceal mucinous neoplasms more frequently harbored concurrent KRAS mutations compared with GNAS wild-type tumors (65% versus 29%, P = .018). GNAS mutations were not significantly associated with overall survival (both with P > .05). Only overall tumor grade was an independent predictor of overall survival in the multivariate analysis (P = .01). Our results indicate that GNAS mutations are frequently identified in both low-grade and high-grade disseminated appendiceal mucinous neoplasms indicating that GNAS mutation status cannot be used to distinguish between low-grade from high-grade appendiceal mucinous neoplasms.

GNAS sequencing identifies IPMN-specific mutations in a subgroup of diminutive pancreatic cysts referred to as "incipient IPMNs"

Incipient intraductal papillary mucinous neoplasms (IPMNs) are poorly described subcentimeter pancreatic cysts with papillae and mucin similar to IPMNs. They are larger than pancreatic intraepithelial neoplasia but do not meet the cutoff size for IPMNs (≥ 1 cm). GNAS codon 201 mutations are hallmark genetic alterations of IPMNs. Hence, we sought to determine the GNAS status of incipient IPMNs to better classify these lesions. Incipient IPMNs from 3 institutions were histologically reassessed, manually microdissected, and the genomic DNA was extracted. Using a sensitive digital ligation technique, the mutational status of KRAS at codon 12 and GNAS at codon 201 was determined. We included 21 incipient IPMNs from 7 male and 12 female patients with a median age of 63 years (range, 40 to 76 y). Most patients underwent surgery for pancreatic ductal adenocarcinoma (N = 8) or ampullary adenocarcinoma (N = 3). The median incipient IPMN size was 4 mm (range, 2 to 7 mm), and a majority had gastric-foveolar (N = 11) or intestinal (N = 5) differentiation. The maximum dysplasia observed was intermediate, and most of the lesions had intermediate-grade dysplasia. Mutational analysis revealed KRAS codon 12 mutations in all 21 incipient IPMNs, whereas 7 lesions (33%) in 7 individual patients harbored GNAS codon 201 mutations. The presence of GNAS 201 mutations in incipient IPMNs suggests that a fraction of these cysts are in fact small IPMNs. Morphologically, incipient IPMNs do not appear to be high-risk lesions. Additional studies in a larger cohort are needed to define the relationship of incipient IPMNs to larger IPMNs and, more importantly, to determine their clinical significance.

A GNAS mutation found in pancreatic intraductal papillary mucinous neoplasms induces drastic alterations of gene expression profiles with upregulation of mucin genes

GNAS, a gene encoding G protein stimulating α subunit, is frequently mutated in intraductal papillary mucinous neoplasms (IPMNs), which are indolent and slow-growing pancreatic tumors that secrete abundant mucin. The GNAS mutation is not observed in conventional ductal adenocarcinomas of the pancreas. To determine the functional significance of the GNAS mutation in pancreatic ductal lineage cells, we examined in vitro phenotypes of cells of pancreatic ductal lineage, HPDE, PK-8, PCI-35, and MIA PaCa-2, with exogenous expression of either wild-type or mutated (R201H) GNAS. We found that exogenous GNAS upregulated intracellular cyclic adenine monophosphate (cAMP), particularly in mutated GNAS transfectants, and upregulated expression of MUC2 and MUC5AC in HPDE and PK-8 cells. By contrast, exogenous GNAS inhibited expression of mucin genes in PCI-35 and MIA PaCa-2 cells, despite upregulation of cAMP. We examined global gene expression profiles of some of the cells transfected with exogenous mutated GNAS (PK-8, PCI-35, and MIA PaCa-2), and found that PK-8 cells exhibited drastic alterations of the gene expression profile, which contrasted with modest alterations in PCI-35 and MIA PaCa-2 cells. To identify a cause of these different effects of exogenous mutated GNAS on phenotypes of the cells, we examined effects of interactions of the signaling pathways of G protein-coupled receptor (GPCR), mitogen-activated protein kinase (MAPK), and phosphatidylinositol 3-kinase (PI3K) on expression of mucin genes. The MAPK and PI3K pathways significantly influenced the expression of mucin genes. Exogenous GNAS did not promote cell growth but suppressed it in some of the cells. In conclusion, mutated GNAS found in IPMNs may extensively alter gene expression profiles, including expression of mucin genes, through the interaction with MAPK and PI3K pathways in pancreatic ductal cells; these changes may determine the characteristic phenotype of IPMN. PK-8 cells expressing exogenous mutated GNAS may be an ideal in vitro model of IPMN.

Analysis of GNAS1 mutations in myxoid soft tissue and bone tumors

The aim of this study was to characterize the prevalence of GNAS1 mutations in various tumor types, including intramuscular myxomas, fibrous dysplasias, and other myxoid tumors and implications for malignant transformation. PCR and direct sequencing were applied to analyze GNAS1 mutation status using genomic DNA isolated from 97 formalin-fixed and paraffin-embedded samples, including 63 intramuscular myxomas, 19 various myxoid lesions, 8 cases of sporadically occurring fibrous dysplasia, and 7 cases of atrial myxoma. Mutations of GNAS1 were detected in 23 out of 63 (36.5%) intramuscular myxoma patients, with mutational hotspots R201H and R201C being equally affected. GNAS1 mutations in codon 201 were found in 5 out of 8 fibrous dysplasias (62.5%), while no mutations of GNAS1 were detected in the other studied entities, including atrial myxomas. GNAS1 mutation analysis has diagnostic value in screening patients with intramuscular myxoma and patients with fibrous dysplasia.

Intramuscular myxoma of the buttock mimicking low-grade fibromyxoid sarcoma: diagnostic usefulness of MUC4 expression

Intramuscular myxoma (IM) is a benign intramuscular neoplasm composed of fibroblasts and abundant myxoid stroma. Some malignant soft tissue tumors can undergo myxomatous degeneration, which makes it difficult to distinguish them from IM. We describe a case of IM of the buttock region mimicking low-grade fibromyxoid sarcoma. The tumor appeared as a well-defined ovoid mass with a cystic lesion on MRI images, and mild uptake on PET images was seen. This was originally misdiagnosed as low-grade fibromyxoid sarcoma (LGFMS) after core-needle biopsy. The mass was excised en bloc and sent for histology. The surgical specimen showed the features of LGFMS with the same characteristics as those mentioned in the previous biopsy report. After surgery, MUC4 expression, a highly sensitive and specific immunohistochemical marker for LGFMS, and FUS gene rearrangement by FISH was not detected upon re-examination; therefore, a conclusive diagnosis of IM was made. The patient had no local recurrence at the 3-year follow-up. Our case suggests that IM with mild FDG uptake is frequently confused with other low-grade malignant myxoid tumors. In addition, absence of MUC4 expression is the definitive key to distinguish IM from LGFMS.

Diagnostic value of investigating GNAS mutations in fibro-osseous lesions: a retrospective study of 91 cases of fibrous dysplasia and 40 other fibro-osseous lesions

GNAS (guanine nucleotide-binding protein/α-subunit) mutations that induce the activation of G-protein α-subunit participate in the pathogenesis of fibrous dysplasia. The aim of this study was to evaluate the sensitivity and specificity of GNAS mutations in fibrous dysplasia and other fibro-osseous lesions, to assess the value of investigating this mutation in the diagnosis of fibro-osseous lesions. We studied 91 cases of fibrous dysplasia. The quality and/or quantity of genomic DNA were suitable for molecular analysis for 51 cases of fibrous dysplasia. GNAS mutations were investigated by three techniques: high-resolution melting (exon 8), allele-specific PCR (exons 8 and 9) and/or direct DNA sequencing (exons 8 and 9). Fibrous dysplasia samples were classified blind to the GNAS mutation status into six histological subtypes as conventional, fibro-involutive, osteosclerosing, cementifying, osteocartilaginous and with prominent aneurysmal cystic changes. We also studied 14 cases of low-grade osteosarcoma, 21 cases of ossifying fibroma, 3 cases of osteofibrous dysplasia, 1 case of osseous dysplasia of the jawbone and 1 post-traumatic lesion of the ribs. Twenty-three cases of fibrous dysplasia (45%) showed mutations of codon 201 (exon 8, p.R201H or p.R201C). No mutation was found on codon 227 (exon 9). GNAS mutations in conventional fibrous dysplasia were detected in the same proportion (47%) as in the other histological subtypes (47%, P=0.96), regardless of sex (P=0.44), age (P=0.90) and location (P=1). GNAS mutations were not detected in any other fibro-osseous lesions. The GNAS mutation was thus specific to fibrous dysplasia in the context of fibro-osseous lesions. The particular mosaicism of mutant and non-mutant cells within the lesion or the existence of other mutations not already described could explain the lack of GNAS mutation in cases of fibrous dysplasia. Investigating this mutation may constitute a valuable complementary diagnostic tool, despite its low sensitivity, particularly in unconventional morphologically different subtypes of fibrous dysplasia.

Enrichment of mutations in multiple DNA sequences using COLD-PCR in emulsion

Background

Multiplex detection of low-level mutant alleles in the presence of wild-type DNA would be useful for several fields of medicine including cancer, pre-natal diagnosis and infectious diseases. COLD-PCR is a recently developed method that enriches low-level mutations during PCR cycling, thus enhancing downstream detection without the need for special reagents or equipment. The approach relies on the differential denaturation of DNA strands which contain Tm-lowering mutations or mismatches, versus ‘homo-duplex’ wild-type DNA. Enabling multiplex-COLD-PCR that can enrich mutations in several amplicons simultaneously is desirable but technically difficult to accomplish. Here we describe the proof of principle of an emulsion-PCR based approach that demonstrates the feasibility of multiplexed-COLD-PCR within a single tube, using commercially available mutated cell lines. This method works best with short amplicons; therefore, it could potentially be used on highly fragmented samples obtained from biological material or FFPE specimens.

Methods

Following a multiplex pre-amplification of TP53 exons from genomic DNA, emulsions which incorporate the multiplex product, PCR reagents and primers specific for a given TP53 exon are prepared. Emulsions with different TP53 targets are then combined in a single tube and a fast-COLD-PCR program that gradually ramps up the denaturation temperature over several PCR cycles is applied (temperature-tolerant, TT-fast-eCOLD-PCR). The range of denaturation temperatures applied encompasses the critical denaturation temperature (T_c) corresponding to all the amplicons included in the reaction, resulting to a gradual enrichment of mutations within all amplicons encompassed by emulsion.

Results

Validation for TT-fast-eCOLD-PCR is provided for TP53 exons 6–9. Using dilutions of mutated cell-line into wild-type DNA, we demonstrate simultaneous mutation enrichment between 7 to 15-fold in all amplicons examined.

Conclusions

TT-fast-eCOLD-PCR expands the versatility of COLD-PCR and enables high-throughput enrichment of low-level mutant alleles over multiple sequences in a single tube.