The role of 18 F-FDG PET/CT in retroperitoneal sarcomas-A multicenter retrospective study

Overview of F18-FDG uptake patterns in retroperitoneal pathologies: imaging findings, pitfalls, and artifacts

INTRODUCTION

Retroperitoneum can be the origin of a wide variety of pathologic conditions and potential space for disease spread to other compartments of the abdomen and pelvis. Computed tomography (CT) and magnetic resonance imaging (MRI) are often the initial imaging modalities to evaluate the retroperitoneal pathologies, however given the intrinsic limitations, F18-FDG PET/CT provides additional valuable metabolic information which can change the patient management and clinical outcomes. We highlight the features of retroperitoneal pathologies on F18-FDG PET/CT and the commonly encountered imaging artifacts and pitfalls. The aim of this review is to characterize primary and secondary retroperitoneal pathologies based on their metabolic features, and correlate PET findings with anatomic imaging.

CONCLUSION

Retroperitoneal pathologies can be complex, ranging from oncologic to a spectrum of non-oncologic disorders. While crosse-sectional imaging (CT and MRI) are often the initial imaging modalities to localize and characterize pathologies, metabolic information provided by F18-FDG PET/CT can change the management and clinical outcome in many cases.

The role of radiation therapy in the management of primary retroperitoneal sarcoma: A systematic review and clinical practice guidelines from the Australia and New Zealand Sarcoma Association

While surgery is the mainstay of treatment for localised retroperitoneal sarcoma, the use of radiotherapy (RT) remains controversial. This systematic review aimed to evaluate the role of RT for retroperitoneal sarcoma. A systematic review using the population, intervention, comparison, and outcome model from 1990 to 2022 identified 66 studies (a mixture of preoperative and postoperative RT); one randomised controlled trial (RCT) with two publications, 18 registry studies, and 46 retrospective studies. In the RCT of preoperative RT, there was no difference in local/abdominal recurrence. The pooled analysis of this RCT and a retrospective study showed a significant abdominal recurrence free survival benefit with preoperative RT in low grade liposarcoma. The RCT and the majority of retrospective series found RT did not improve recurrence free survival (11 of 16 no difference in combined local and distant RFS, 11 of 13 no difference in distant metastasis free survival), disease specific survival (9 of 12 studies) or overall survival (33 of 49 studies). The majority of studies found no association between RT and perioperative morbidity. In summary, preoperative RT may improve local control for low grade (well-differentiated or grades 1-2 dedifferentiated) liposarcoma, but not other histological subtypes. There is no strong evidence that perioperative RT provides an overall survival benefit. Patients with low grade retroperitoneal liposarcoma can be considered for preoperative RT to improve abdominal recurrence free survival. The rationale and level of evidence in this scenario should be carefully discussed by the multidisciplinary team with patients. RT should not be routinely recommended for other histological subtypes.

Management of recurrent retroperitoneal sarcomas

Recurrent retroperitoneal sarcomas are rare, with patterns of recurrence determined by the histologic subtype. A range of patient characteristics and treatment profiles combined with a myriad of presentations and clinical courses of recurrences make this diverse entity challenging to manage. Although surgical resection improves survival in select patients, the oncological outcomes are inferior to that of primary retroperitoneal sarcomas. Management options for unresectable disease include local ablative therapy, radiation and systemic therapy, with palliative surgery indicated occasionally. Attempts at disease control must be balanced with potential morbidity and impact on the patient's quality of life. This review aims to offer insights into the current understanding of recurrent retroperitoneal sarcomas and provide some guidance on management.

How to treat liposarcomas located in retroperitoneum

Almost half of retroperitoneal (RP) sarcomas are liposarcomas (LPS). The large majority of RP LPS are either well-differentiated LPS (WDLPS) or dedifferentiated LPS (DDLPS), these latter further classified according to grading in G2 and G3 DDLPS. Surgery is the only potentially curative treatment to achieve local control and possibly cure in primary localized disease. Over the last decade, a better delineation of the different histology-specific patterns of failure and the development of nomograms predictors of outcome has led to a better management of these rare tumors, with a special focus on non-surgical treatments. Available evidences - although far from exhaustive - show that radiation therapy might have a role, if any, as neoadjuvant treatment in locally aggressive histologies (i.e. WDLPS and G2 DDLPS), while it does not seem beneficial for histologies with a higher metastatic risk (i.e. G3 DDLPS and leiomyosarcoma). Neoadjuvant chemotherapy, instead, can be considered to reduce the risk of distant metastasis while waiting for the results of an ongoing RCT (STRASS-2) evaluating its effect in these tumors. However, given the rarity of these diseases and the subsequent lack of strong evidences to guide treatment, outcome improvement in these patients remains a challenge. Patients' referral to a sarcoma center where a dedicated specialized multidisciplinary team tailor optimal treatment on a case-by-case basis is crucial to ensure these patients the best outcome. Refining available nomograms - e.g including molecular variables - and identifying predictors of response/toxicity to chemotherapy and immunotherapy might be significantly helpful in tailoring treatments to the patient's characteristics. Also, new systemic agents are eagerly awaited for improving the management further.

CT and MR Imaging of Retroperitoneal Sarcomas: A Practical Guide for the Radiologist

Primary retroperitoneal sarcomas (RPS) represent around 10-16% of all sarcomas, with liposarcomas and leiomyosarcomas being the most common subtypes. RPS have some peculiar characteristics, imaging appearances, worse prognosis, and complications compared to other locations of sarcoma. Commonly, RPS primarily present as large masses, progressively encasing adjacent structures, causing mass effect, and complications. RPS diagnosis is often challenging, and these tumors may be overlooked; however, failure to recognize RPS characteristics leads to a worse prognosis for the patients. Surgery is the only recognized curative treatment, but the anatomical constraints of the retroperitoneum limit the ability to achieve wide resection margins; therefore, these tumors have a high rate of recurrence, and require long-term follow-up. The radiologist has an important role in the diagnosis of RPS, the definition of their extent, and their follow-up. Specific knowledge of the main imaging findings is required to reach an early diagnosis, and, ultimately, to guarantee the best patient management. This article provides an overview of the current knowledge regarding cross-sectional imaging features of patients with retroperitoneal sarcomas, presenting tips and tricks to improve imaging diagnosis of RPS.

Surgical Management of Retroperitoneal Sarcoma

Surgery is the cornerstone of treatment for retroperitoneal sarcoma (RPS). Surgery should be performed by a surgical oncologist with sub-specialization in this disease and in the context of a multidisciplinary team of sarcoma specialists. For primary RPS, the goal of surgery is to achieve the complete en bloc resection of the tumor along with involved organs and structures to maximize the clearance of the disease. The extent of resection also needs to consider the risk of complications. Unfortunately, the overarching challenge in primary RPS treatment is that even with optimal surgery, tumor recurrence occurs frequently. The pattern of recurrence after surgery (e.g., local versus distant) is strongly associated with the specific histologic type of RPS. Radiation and systemic therapy may improve outcomes in RPS and there is emerging data studying the benefit of non-surgical treatments in primary disease. Topics in need of further investigation include criteria for unresectability and management of locally recurrent disease. Moving forward, global collaboration among RPS specialists will be key for continuing to advance our understanding of this disease and find more effective treatments.

Which modality is better to diagnose high-grade transformation in retroperitoneal liposarcoma? Comparison of computed tomography, positron emission tomography, and magnetic resonance imaging

BACKGROUND

Survival in patients with retroperitoneal liposarcoma (RPLS) depends on the surgical management of the dedifferentiated foci. The present study investigated the diagnostic yield of contrast-enhanced CT, ¹⁸F-fluorodeoxyglucose positron emission tomography (PET), and diffusion-weighted MRI in terms of dedifferentiated foci within the RPLS.

METHODS

Patients treated with primary or recurrent RPLS who underwent the above imaging between January 2010 and December 2021 were retrospectively reviewed. The diagnostic accuracy of the three modalities for histologic subtype of dedifferentiated liposarcoma (DDLS) and French Federation of Cancer Center (FNCLCC) grade 2/3 were compared using receiver operating characteristic curves and areas under the curves (AUCs).

RESULTS

The cohort involved 32 patients with 53 tumors; 30 of which exhibited DDLS and 31 of which did FNCLCC grades 2/3. The optimal thresholds for predicting DDLS were mean CT value of 31 Hounsfield Unit (HU) (AUC = 0.880, 95% CI 0.775-0.984; p < 0.001), maximum standardized uptake value (SUVmax) of 2.9 (AUC = 0.865 95% CI 0.792-0.980; p < 0.001), while MRI failed to differentiate DDLS. The cutoff values for distinguishing FNCLCC grades 1 and 2/3 were a mean CT value of 24 HU (AUC = 0.858, 95% CI 0.731-0.985; p < 0.001) and SUVmax of 2.9 (AUC = 0.885, 95% CI 0.792-0.978; p < 0.001). MRI had no sufficient power to separate these grades.

CONCLUSIONS

Contrast-enhanced CT and PET were useful for predicting DDLS and FNCLCC grade 2/3, while MRI was inferior to these two modalities.

Management of Recurrent Retroperitoneal Sarcoma

Recurrence after resection of retroperitoneal sarcoma is common and varies by histological subtype. Pattern of recurrence is similarly affected by histology (e.g., well-differentiated liposarcoma is more likely to recur locoregionally, whereas leiomyosarcoma is more likely to develop distant metastases). Radiotherapy may provide effective locoregional control in limited circumstances and the data on the impact of chemotherapy are scant. Surgery for locally recurrent disease is associated with the greatest survival benefit; however, data are retrospective and from a highly selected subgroup of patients. Limited retrospective data have also suggested a survival association with the resection of limited distant metastases. Given the complexity of these patients, multidisciplinary evaluation at a high-volume sarcoma center is critical.

Head pleomorphic sarcoma showing murine double minute 2 amplification without a well-differentiated liposarcoma component in a pediatric patient

BACKGROUND

Murine double minute 2 (MDM2) is an oncogene that inhibits p53, leading to decreased apoptosis. Sarcomas showing MDM2 amplification are rare among pediatric patients.

CASE

A 14-year-old boy presented with pleomorphic sarcoma of the head showing MDM2 amplification without a well-differentiated liposarcoma component. Although chemotherapy was initially performed to reduce the tumor size before surgery, the tumor did not shrink. The patient underwent complete surgical resection. Microscopic examination revealed a positive surgical margin; thus, postoperative proton-beam radiotherapy was performed. 3 years after the therapy, no sign of recurrence was observed.

CONCLUSION

Macroscopic surgical resection combined with adjuvant postoperative radiotherapy was effective against MDM2-amplified pleomorphic sarcoma refractory to neoadjuvant chemotherapy in a pediatric patient.

Giant retroperitoneal dedifferentiated liposarcoma mimicking ovarian cancer: A case report

•

Clinical features of the dedifferentiated subtype of LPS that has a diameter of >30 cm remains unknown.

•

Surgical resection entails a high risk due to the size and anatomical location and difficulty in preoperative diagnosis.

•

CT is the most useful imaging method for evaluating tumor location, size, origin, and relationship to adjacent organs.

•

Retroperitoneal LPS should be considered in the case of a giant intra-abdominal tumor with a fatty component.

•

Surgical resection is the mainstay of treatment for retroperitoneal LPS.

Retroperitoneal liposarcoma is a rare tumor, and its dedifferentiated subtype and a larger diameter are associated with a poor prognosis. However, there are few reports of retroperitoneal liposarcomas, both with a dedifferentiated subtype and a diameter of >30 cm. We report a case of a giant retroperitoneal liposarcoma with a dedifferentiated subtype. A 78-year-old woman presented to our hospital with abdominal distension and loss of appetite. Computed tomography and magnetic resonance imaging findings revealed a 35-cm-diameter solid tumor in the peritoneal cavity. CA125 (64.8 U/mL) and HE4 (229.0 pmol/L) were elevated preoperatively raising suspicion for ovarian malignancy. However, intraoperative findings revealed that the tumor originated in the retroperitoneal cavity. Reductive surgery for the tumor and partial resection of the sigmoid colon and left ureter were performed, and pathological examination confirmed a retroperitoneal dedifferentiated liposarcoma. Although her symptoms improved postoperatively, she died 11 months after surgery due to disease progression.

Is preoperative CT-guided biopsy a valuable tool in the diagnostic workup of patients with visceral and retroperitoneal sarcoma?

PURPOSE

We aimed to analyze the diagnostic accuracy of preoperative CT-guided biopsy to identify patients that might profit from neoadjuvant chemotherapy in a specialized high-volume sarcoma center.

MATERIAL AND METHODS

We retrospectively reviewed all patients with suspected soft tissue tumors of the abdomen cavity including the retroperitoneum, who received CT-guided biopsy followed by surgical tumor resection. Sensitivity, specificity, PPV and NPV were calculated in all patients with abdominal sarcomas at our hospital. A subgroup analysis was performed for patients with liposarcoma.

RESULTS

A total of 82 patients (35 female, 47 male, age: 62.0 ± 14.7) received preoperative CT-guided biopsy followed by surgical resection. Overall accordance of CT-guided biopsy to identify final histology was 77 %. CT-guided biopsy revealed the diagnosis of liposarcoma in 23 patients whereas final analysis of the surgical specimen identified liposarcoma in 29 patients. Here, sensitivity, specificity, PPV and NPV was 79.3 %, 100.0 %, 100.0 % and 89.8 % respectively. Subgroup analysis revealed a better accuracy for correctly identifying patients with well-differentiated liposarcoma than patients with dedifferentiated liposarcoma (75.0 % vs 62.5 %). In patients with other sarcoma, sensitivity, specificity, PPV, NPV and diagnostic accuracy was 87.5 %, 95.5 %, 82.4 % and 96.9 %, respectively.

CONCLUSION

CT-guided biopsy in a specialized high-volume sarcoma center is an accurate and effective method to assess patients with abdominal sarcoma and especially abdominal liposarcoma. Therefore, it is an indispensable tool in the pretherapeutic workup process. Nevertheless, our study underlines the previously reported difficulties in dedifferentiated liposarcoma diagnostics, whereby these patient cohort would profit the most from a neoadjuvant therapy regime.

Retroperitoneal and Mesenteric Liposarcomas

Retroperitoneal liposarcomas are a rare entity and are comprised mostly of the well-differentiated and dedifferentiated subtypes. Eight-year survival ranges from 30% to 80% depending on histologic subtype and grade. Surgery is the cornerstone of treatment and compartment resection is the current standard. Mesenteric liposarcomas are extremely rare and comprise more high-grade lesions, with poorer prognosis of 50% 5-year overall survival. They are managed with a similar aggressive surgical approach. This review presents the current management of retroperitoneal and mesenteric liposarcomas.

Management of Locally Recurrent Retroperitoneal Sarcoma in the Adult: An Updated Consensus Approach from the Transatlantic Australasian Retroperitoneal Sarcoma Working Group

BACKGROUND

Surgery is the mainstay of treatment for retroperitoneal sarcoma (RPS), but local recurrence is common. Biologic behavior and recurrence patterns differ significantly among histologic types of RPS, with implications for management. The Transatlantic Australasian RPS Working Group (TARPSWG) published a consensus approach to primary RPS, and to complement this, one for recurrent RPS in 2016. Since then, additional studies have been published, and collaborative discussion is ongoing to address the clinical challenges of local recurrence in RPS.

METHODS

An extensive literature search was performed, and the previous consensus statements for recurrent RPS were updated after review by TARPSWG members. The search included the most common RPS histologic types: liposarcoma, leiomyosarcoma, solitary fibrous tumor, undifferentiated pleomorphic sarcoma, and malignant peripheral nerve sheath tumor.

RESULTS

Recurrent RPS management was evaluated from diagnosis to follow-up evaluation. For appropriately selected patients, resection is safe. Nomograms currently are available to help predict outcome after resection. These and other new findings have been combined with expert recommendations to provide 36 statements, each of which is attributed a level of evidence and grade of recommendation. In this updated document, more emphasis is placed on histologic type and clarification of the intent for surgical treatment, either curative or palliative. Overall, the fundamental tenet of optimal care for patients with recurrent RPS remains individualized treatment after multidisciplinary discussion by an experienced team with expertise in RPS.

CONCLUSIONS

Updated consensus recommendations are provided to help guide decision-making for treatment of locally recurrent RPS and better selection of patients who would potentially benefit from surgery.

Development and Validation of a Prognostic Model to Predict the Prognosis of Patients With Retroperitoneal Liposarcoma: A Large International Population-Based Cohort Study

Background

Retroperitoneal liposarcomas (RPLs), sarcoma of mesenchymal origin, are the most common soft tissue sarcomas (STS) of the retroperitoneum. Given the rarity of RPLs, the prognostic values of clinicopathological features in the patients remain unclear. The nomogram can provide a visual interface to aid in calculating the predicted probability that a patient will achieve a particular clinical endpoint and communication with patients.

Methods

We included a total of 1,392 RPLs patients diagnosed between 2004 and 2015 from the Surveillance, Epidemiology, and End Results (SEER) database. For nomogram construction and validation, patients in the SEER database were divided randomly into the training cohort and internal validation cohort at a ratio of 7:3, while 65 patients with RPLs from our center between 2010 and 2016 served as the external validation cohort. The OS curves were drawn using the Kaplan–Meier method and assessed using the log-rank test. Moreover, Fine and Gray’s competing-risk regression models were conducted to assess CSS. Univariate and multivariate analyses were performed to select the prognostic factors for survival time. We constructed a predictive nomogram based on the results of the multivariate analyses.

Results

Through univariate and multivariate analyses, it is found that age, histological grade, classification, SEER stage, surgery constitute significant risk factors for OS, and age, classification, SEER stage, AJCC M stage, surgery, and tumor size constitute risk factors for CSS. We found that the nomogram provided a good assessment of OS and CSS at 1, 3, and 5 years in patients with RPLs (1-year OS: (training cohort: AUC = 0.755 (95% CI, 0.714, 0.796); internal validation cohort: AUC = 0.754 (95% CI, 0.681, 0.827); external validation cohort: AUC = 0.793 (95% CI, 0.651, 0.935)); 3-year OS: (training cohort: AUC = 0.782 (95% CI, 0.752, 0.811); internal validation cohort: AUC = 0.788 (95% CI, 0.736, 0.841); external validation cohort: AUC = 0.863 (95% CI, 0.773, 0.954)); 5-year OS: (training cohort: AUC = 0.780 (95% CI, 0.752, 0.808); internal validation cohort: AUC = 0.783 (95% CI, 0.732, 0.834); external validation cohort: AUC = 0.854 (95% CI, 0.762, 0.945)); 1-year CSS: (training cohort: AUC = 0.769 (95% CI, 0.717, 0.821); internal validation cohort: AUC = 0.753 (95% CI, 0.668, 0.838); external validation cohort: AUC = 0.799 (95% CI, 0.616, 0.981)); 3-year CSS: (training cohort: AUC = 0.777 (95% CI, 0.742, 0.811); internal validation cohort: AUC = 0.787 (95% CI, 0.726, 0.849); external validation cohort: AUC = 0.808 (95% CI, 0.673, 0.943)); 5-year CSS: (training cohort: AUC = 0.773 (95% CI, 0.741, 0.805); internal validation cohort: AUC = 0.768 (95% CI, 0.709, 0.827); external validation cohort: AUC = 0.829 (95% CI, 0.712, 0.945))). The calibration plots for the training, internal validation, and external validation cohorts at 1-, 3-, and 5-year OS and CSS indicated that the predicted survival rates closely correspond to the actual survival rates.

Conclusion

We constructed and externally validated an unprecedented nomogram prognostic model for patients with RPLs. The nomogram can be used as a potential, objective, and supplementary tool for clinicians to predict the prognosis of RPLs patients around the world.

PET-CT in Clinical Adult Oncology-VI. Primary Cutaneous Cancer, Sarcomas and Neuroendocrine Tumors

PET-CT is an advanced imaging modality with many oncologic applications, including staging, therapeutic assessment, restaging and surveillance for recurrence. The goal of this series of six review articles is to provide practical information to providers and imaging professionals regarding the best use of PET-CT for specific oncologic indications, the potential pitfalls and nuances that characterize these applications, and guidelines for image interpretation. Tumor-specific clinical information and representative PET-CT images are provided. The current, sixth article in this series addresses PET-CT in an evaluation of aggressive cutaneous malignancies, sarcomas and neuroendocrine tumors. A discussion of the role of FDG PET for all types of tumors in these categories is beyond the scope of this review. Rather, this article focuses on the most common malignancies in adult patients encountered in clinical practice. It also focuses on Food and Drug Agency (FDA)-approved and clinically available radiopharmaceuticals rather than research tracers or those requiring a local cyclotron. This information will serve as a guide to primary providers for the appropriate role of PET-CT in managing patients with cutaneous malignancies, sarcomas and neuroendocrine tumors. The nuances of PET-CT interpretation as a practical guide for imaging providers, including radiologists, nuclear medicine physicians and their trainees, are also addressed.

Pancreatic liposarcoma: a case report

An 81-year-old woman who had undergone total thyroidectomy for papillary thyroid cancer 12 years earlier was found to have a tumor in the tail of the pancreas. Four years earlier, skin, lung, and mediastinal lymph node metastases had appeared. Computed tomography (CT) showed a mass 26 mm in diameter in the tail of the pancreas. Thereafter, the pancreatic tumor increased in size, while the lung metastases remained stable. Unenhanced CT at the time of first detection showed that the tumor was heterogeneous, with low-attenuation areas indicating fat components. As the tumor grew, the fat components became unclear. Laparoscopic distal pancreatectomy and splenectomy were performed. The tumor was diagnosed as dedifferentiated liposarcoma with a well-differentiated liposarcoma component at the tumor margin. The pancreas is an extremely rare site of primary liposarcoma. In the present case, a pancreatic liposarcoma appeared during follow-up of thyroid cancer, and the changes over time were able to be observed with CT.

The Role of Preoperative 18F-fluorodeoxyglucose Positron Emission Tomography/Computed Tomography in Retroperitoneal Sarcoma

¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) was used to predict pathologic grades based on the maximum standardized uptake value (SUVmax) in soft tissue sarcoma and bone sarcoma. In retroperitoneal sarcoma (RPS), the effectiveness of PET was not well known. This study was designed to investigate the association of SUVmax with histopathologic grade and evaluate the usefulness of ¹⁸F-FDG PET/CT before operation. Patients at Samsung Medical Center undergoing primary surgery for retroperitoneal sarcoma with preoperative ¹⁸F-FDG PET/CT imaging between January 2001 and February 2020 were investigated. The relationship between SUVmax and histologic features was assessed. The association of SUVmax with overall survival (OS), local recurrence (LR), and distant metastasis (DM) were studied. Of the total 129 patients, the most common histologic subtypes were liposarcoma (LPS; 68.2%) and leiomyosarcoma (LMS; 15.5%). The median SUVmax was 4.5 (range, 1- 29). Moreover, SUVmax was correlated with tumor grade (p < 0.001, Spearman coefficient; 0.627) and mitosis (p < 0.001, Spearman coefficient; 0.564) and showed a higher value in LMS (12.04 ± 6.73) than in dedifferentiated liposarcoma (DDLPS; 6.32 ± 4.97, p = 0.0054). SUVmax was correlated with pathologic parameters (tumor grade and mitosis) in RPS and was higher in the LMS group than the DDLPS group. The optimal SUVmax threshold to distinguish high tumor grade was 4.8. Those with a SUVmax greater than the threshold showed poor prognosis regarding OS, LR, and DM (p < 0.001).

18F-Fluorodeoxyglucose Positron Emission Tomography Is Useful in the Evaluation of Prognosis in Retroperitoneal Sarcoma

Simple Summary

Retroperitoneal sarcomas are difficult malignancies to treat because complete surgical resection is the only effective treatment option, but it is difficult to secure sufficient surgical margins. It is essential for developing a treatment strategy to assess tumor aggressiveness and predict prognosis for patients. However, the aggressiveness of retroperitoneal sarcomas before treatment cannot be fully evaluated. In patients with resectable soft tissue sarcomas or several carcinomas, SUV evaluated with FDG-PET has been reported to be a valuable prognostic parameter. However, the correlation between SUVmax on FDG-PET and the prognosis of several histological subtypes in retroperitoneal sarcoma, including dedifferentiated liposarcoma, well-differentiated liposarcoma, and leiomyosarcoma, remains uncertain. This study revealed that SUVmax calculated with FDG-PET was useful as a prognostic factor in retroperitoneal sarcoma, especially in dedifferentiated liposarcoma and Grade2 retroperitoneal sarcoma.

Abstract

Background: Retroperitoneal sarcomas are rare neoplasms that occur in the retroperitoneum. Complete surgical resection is the only effective treatment option. The prediction of prognosis by histological diagnosis has not yet been established. The purpose of this study was to identify the usefulness of [18-F] fluorodeoxyglucose (FDG) positron emission tomography (PET) imaging for validating the prognosis of retroperitoneal sarcoma (RPS) established by histological diagnosis. Methods: We retrospectively reviewed 201 patients with RPS treated at the Osaka International Cancer Institute between 2010 and 2021. We extracted the clinical data, including standardized uptake values (SUVs), evaluated with FDG-PET, and statistically analyzed the data. Results: The median age of patients was 64 years (range, 31–85 years). A total of 101 (50.2%) patients were men, and 100 (49.8%) were women. Surgical resection was performed in 155 (77.1%) patients. On histological analysis, 75 (37.3%), 52 (25.9%), and 29 (14.4%) patients were diagnosed with dedifferentiated liposarcoma, well-differentiated liposarcoma, and leiomyosarcoma, respectively. The median survival time for patients with high maximum SUV (SUVmax) (≥4) or low SUVmax (<4) was 275.8 months and 79.5 months, respectively. Furthermore, among the patients with dedifferentiated liposarcoma, the overall survival rate for patients with high SUVmax (≥4) was significantly lower than that of those with low SUVmax (<4). Conclusions: The present study demonstrated that SUVmax calculated with FDG-PET was useful as a prognostic factor in RPS, especially in dedifferentiated liposarcoma and Grade2 RPS. To devise a treatment strategy for RPS, SUVmax during FDG-PET scan may be considered for clinical assessment.

PET/CT variants and pitfalls in bone and soft tissue sarcoma

Sarcomas are rare tumors of mesenchymal origin and comprise only around 1% of adult cancers. The abundance of sarcoma histiotypes, with distinct imaging characteristics, biology, clinical behavior and treatment strategy, result in a complex disease presentation, requiring management by multidisciplinary specialized sarcoma centers. Oncologic and musculoskeletal radiology guidelines provide minimal guidance and only fragmentary information on the indications of ¹⁸F-FDG PET/CT in sarcoma. Therefore, knowledge of various phenotypes with preference for bone and lymph node metastases or higher incidence of local and distant recurrence is essential to select the appropriate diagnostic imaging tests and its interpretation. Benign and malignant soft tissue and bone tumors often share common radiographic and metabolic imaging characteristics. In addition, metastases of various histiotypes might exhibit a spectrum of atypical imaging appearances. Therefore, imaging specialists need to be aware of these variants and associated pitfalls of sarcoma imaging.