Metastasis-directed therapy in testicular cancer.

PURPOSE OF REVIEW: This review highlights the importance of addressing testicular cancer metastasizing beyond the retroperitoneum, focusing on multidisciplinary approaches and advances in treatment. RECENT FINDINGS: Recent literature emphasizes on the evolving landscape of metastasis-directed therapy, including surgical interventions, chemotherapy regimens, and radiation therapy. The effectiveness of these treatments varies depending on the site of metastasis, with various approaches improving survival rates and quality of life for patients. We divide our review in an organ-specific manner and focus on chemotherapeutic, surgical, and radiation therapy approaches pertaining to each site of metastasis. SUMMARY: Our review suggests the pressing need for continued research to refine and personalize treatment strategies. These efforts are important for enhancing clinical practice, ultimately leading to better outcomes for patients with metastatic testicular cancer.

Diagnosis and treatment of malignant retroperitoneal mesothelioma: A case report.

RATIONALE: Malignant peritoneal mesothelioma (MPM) is a rare clinical disease. Although there are several reports describing intraperitoneal mesothelioma of the lung, liver, and intestine, retroperitoneal mesothelioma is, to our knowledge, very rare and rarely reported. In recent years, our best clinical protocols for the treatment and diagnosis of retroperitoneal mesothelioma have not been proven and the diagnosis and treatment are challenging. PATIENT CONCERNS: A 37-year-old Chinese woman complained of bilateral low back pain for a month, with obvious symptoms of low back pain on the left side. To treat low back pain, retroperitoneal masses were found during physical examination. The patient consulted a urological specialist for further treatment. DIAGNOSIS: After the operation, pathological biopsy confirmed retroperitoneal epithelioid diffuse mesothelioma. INTERVENTIONS: After exclusion of surgical contraindications, the patient underwent laparoscopic retroperitoneal lesion resection under tracheal intubation and general anesthesia, and the operation was successful. OUTCOMES: On the tenth day after surgery, the patient vital signs were stable, and he was discharged. LESSONS: Patients with malignant peritoneal mesothelioma may have no typical clinical symptoms, and the diagnosis is based on pathological and immunohistochemical examination. In selected patients, surgical cell reduction and intraoperative intraperitoneal heat chemotherapy have become the first choice of treatment, which can achieve ideal therapeutic effects and prolong survival.

Advancements in Diagnosis and Multimodal Treatment Strategies for Retroperitoneal Tumors: A Comprehensive Review.

Retroperitoneal tumors (RPTs) encompass both benign and malignant entities, constituting ~0.1% to 0.2% of all malignant tumors, of which 70% to 80% manifest malignancy. Predominantly, retroperitoneal sarcomas (RPS) represent the most prevalent subtype among RPT. With over 70 histologic forms identified, liposarcomas and leiomyosarcomas emerge as the primary constituents of RPS. Accurate diagnosis of RPTs necessitates preoperative core-needle biopsy and comprehensive imaging assessment. The current staging protocol for RPS relies on the eighth edition of the American Joint Committee on Cancer/TNM classification. Surgical excision remains the established gold standard for treating RPS. Therapeutic approaches vary according to the underlying pathophysiology. Although chemotherapy and radiotherapy exhibit efficacy in managing metastatic and recurrent unresectable RPS, their role in primary RPS remains unresolved, necessitating further clinical trials for validation. Concurrently, ongoing research explores the potential of targeted therapies and immunotherapy. This literature review aims to provide a comprehensive overview of existing research, delineating diagnostic pathways and optimal therapeutic strategies for RPT.

Treatment of retroperitoneal sarcoma results in improved outcomes.

OBJECTIVE: To report the clinical characteristics, treatments, and outcomes in a cohort of dogs with histologically confirmed retroperitoneal sarcoma (RPS) and to identify potential variables of prognostic significance. ANIMALS: 46 client-owned dogs from 10 clinics with histopathologic diagnosis of a sarcoma originating from the retroperitoneal space. METHODS: Medical records were retrospectively reviewed to obtain information regarding clinical characteristics, treatments, and outcomes. Recorded variables were analyzed to report descriptive data for all cases and overall survival time. Multivariate analysis was utilized to evaluate prognostic factors for overall survival. RESULTS: Hemangiosarcoma was the most common histologic subtype diagnosed (76.1%). Cytoreductive and curative intent surgical excision of the RPS was attempted in 12 and 22 dogs, respectively; 12 dogs underwent no surgery or had an exploratory laparotomy with incisional biopsy only. Nineteen dogs received adjuvant chemotherapy, either injectable or metronomic, and 1 dog received adjuvant radiation therapy. Fourteen of the 34 (41.2%) surgically treated dogs developed evidence of local recurrence, but there was no difference in local recurrence when comparing dogs categorized as curative intent versus cytoreductive surgery. The median overall survival time was 238 days. On multivariable analysis, treatment approach was associated with survival with surgical excision (vs palliative treatment) and adjuvant chemotherapy following surgery being protective against death. A diagnosis of hemangiosarcoma was associated with a greater hazard of death. CLINICAL RELEVANCE: This study demonstrates a substantially greater survival time than previously published and suggests a survival benefit from surgical excision and adjuvant chemotherapy.

Retroperitoneal sarcoma: a 10-year follow-up analysis using hospital-based cancer registry data in Japan.

OBJECTIVES: We sought clinical characteristics, survival outcomes, and prognostic factors for overall survival of retroperitoneal sarcoma in Japan. METHODS: A Japanese hospital-based cancer registry database with a pivotal 10-year follow-up was used to identify and enroll patients, registered from 106 institutions, diagnosed with retroperitoneal sarcoma in 2008-2009. Treating hospitals were divided by hospital care volume; high-volume hospitals and low-volume hospitals were defined as ≥ 4 and < 4 cases/year, respectively. RESULTS: A total of 91 men and 97 women were included, with a median age of 64 years. The most common histological type was liposarcoma in 101 patients, followed by leiomyosarcoma in 38 patients. The 5-year and 10-year overall survival rates were 44.1 and 28.3%. The majority of patients (n = 152, 80.9%) were treated at low-volume hospitals. High-volume hospital patients had higher 10-year overall survival rates than low-volume hospital patients (51.2% vs 23.2%, P = 0.026). Multivariate analysis revealed age over 60 years, treatment in low-volume hospitals and chemotherapy were independent predictors of unfavorable survival while treatment with surgery was an independent predictor of favorable survival. CONCLUSIONS: The possibility of surgical removal was suggested to be the most important prognostic factor for retroperitoneal sarcoma. Better survival was shown in patients treated at high-volume hospitals in our series.

Pediatric retroperitoneal non-organ-originated malignancies: An analysis based on SEER database.

Retroperitoneal non-organ-originated malignancies are rare pediatric tumors with challenging diagnosis and treatment. The present study aimed to analyze the clinicopathological characteristics, treatment, and prognosis of retroperitoneal non-organ-originated malignancies. In the study, we included the pathological diagnosis of pediatric retroperitoneal non-organ-originated malignant tumors between 2000 to 2019 through the updated Surveillance, Epidemiology, and End Results database. We use the Kaplan-Meier survival curve to calculate the overall survival (OS) and cancer-specific survival (CSS). The risk of all-cause death and disease-specific death were analyzed using Cox proportional hazard regression model and Fine-and-Grey competitive hazard model, respectively. In the study, a total of 443 pediatric retroperitoneal non-organ-originated malignancies were included. Of them, only 22.3% of patients had no metastatic disease, 42.9% had distant metastasis and 34.8% had locally advanced diseases. The primary pathological tumor was neuroblastoma followed by germ cell tumor. The overall 10-year OS and CSS were 70.7% and 73.1%, respectively, and the 10-year OS and CSS of metastatic diseases were 54.4% and 56.6%, respectively. Older children, worse tumor stage at diagnosis, incomplete resection, and prolonged time from diagnosis to treatment were significantly associated with worse survival outcomes. Radiotherapy and chemotherapy did not significantly improve the prognosis of patients without complete tumor resection. The study indicated that most pediatric retroperitoneal non-organ-originated malignancies diagnosed with metastatic diseases have plagued treatment. Radiotherapy and chemotherapy are the main treatment methods for children unable to undergo complete surgical treatment. However, these treatments do not reach the same therapeutic effect as complete tumor resection after early diagnosis. Hence, early diagnosis and surgery for complete tumor resection are of utmost importance.

Practical Management of Adult Ultra-Rare Primary Retroperitoneal Soft Tissue Sarcoma: A Focus on Perivascular Epithelioid Tumours and Extraosseous Ewing Sarcoma.

With the exception of well-differentiated liposarcoma, dedifferentiated liposarcoma, leiomyosarcoma, solitary fibrous tumour, malignant peripheral nerve sheath tumour, and undifferentiated pleomorphic sarcoma, the majority of the ≈70 histologic subtypes of retroperitoneal sarcoma are defined as 'ultra-rare' sarcomas, with an incidence of ≤1-5/1,000,000 persons/year. For most of these ultra-rare RPS subtypes, diagnosis and treatment follows international guidelines for the management of more common RPS histologies, with en bloc surgical resection as the mainstay of curative treatment, and enrolment in clinical trials where possible. Because the treatment of RPS is heavily driven by histology, the surgeon must be familiar with specific issues related to the diagnosis and management of ultra-rare sarcoma subtypes. Expert radiological and surgeon reviews are required to differentiate similarly presenting tumours where surgery can be avoided (e.g., angiomyolipoma), or where upfront systemic therapy is indicated (e.g., extraosseous Ewing's sarcoma). Thus, the management of all retroperitoneal sarcomas should occur at a sarcoma referral centre, with a multidisciplinary team of experts dedicated to the surgical and medical management of these rare tumours. In this focused review, we highlight how diagnosis and management of the ultra-rare primary RPS histologies of malignant perivascular epithelioid cell tumour (PEComa), extraosseous Ewing sarcoma (EES), extraosseous osteosarcoma (EOS), and rhabdomyosarcoma (RMS) critically diverge from the management of more common RPS subtypes.

Primary retroperitoneal squamous cell carcinoma: a literature review.

PURPOSE: Retroperitoneal squamous cell carcinoma is an extremely rare histological variant of retroperitoneal tumors. The exact etiology and origin of the same is still unknown. To date, only a few case reports have been published in the literature. Due to rarity, standard treatment protocol is not available. The article aims to review the literature and treatment options available for this uncommon entity, based on available data. METHODS: We searched the databases like PubMed, PubMed Central, Scopus, and Google Scholar with the keywords "Squamous cell carcinoma" and "retroperitoneal tumors". Peer-reviewed and recent articles were screened. RESULTS: Seven relevant articles comprising 14 cases were found. Due to the small number of reports, tabulation of treatment details and outcome was done. Like the sarcoma variant, these tumors also present with a large mass in the abdomen and abdominal discomfort. Association with human papillomavirus appears to be the most common factor that gives rise to squamous histology. CONCLUSION: Retroperitoneal SCC is an uncommonly diagnosed entity. Although no specific treatment guidelines exist for this uncommon malignancy; surgery followed by adjuvant or definitive radiotherapy with concurrent chemotherapy (in inoperable cases) seems a feasible option. Multicentre trials should be conducted for establishing definitive treatment strategies for this ailment.

Large retroperitoneal extraskeletal Ewing's sarcoma with renal pedicle invasion: a case report.

BACKGROUND: Extraskeletal Ewing's sarcoma (EES) is a rare malignant tumor primarily found in children and young adults. Localized disease can present with nonspecific symptoms such as local mass, regional pain, and increased skin temperature. More severe cases may present with systemic symptoms such as malaise, weakness, fever, anemia, and weight loss. Among these lesions, retroperitoneal sarcomas are relatively uncommon and difficult to diagnose. Since they are usually asymptomatic until large enough to compress or invade the surrounding tissues, most are already advanced at first detection. Traditionally, the treatment of choice is complete surgical resection, sometimes combined with postoperative radiotherapy and chemotherapy. We report a case of EES with left renal artery invasion in the left retroperitoneal cavity successfully treated with transarterial embolization and surgery. CASE PRESENTATION: A 57-year-old woman with a negative family history of cancer presented at our Urology Department with a large left retroperitoneal tumor found by magnetic resonance imaging during the health exam. Physical examination showed a soft abdomen and no palpable mass or tenderness. Imaging studies showed that the tumor covered the entire left renal pedicle, but the left kidney, left adrenal gland, and pancreas appeared tumor free. Since the tumor tightly covered the entire renal pedicle, tumor excision with radical nephrectomy was advised. The patient underwent transarterial embolization of the left renal artery with 10 mg of Gelfoam pieces daily before surgical excision. Tumor excision and left radical nephrectomy were uneventful the day after embolization. Post-operatively, the patient recovered well and was discharged on day 10. The final histopathological analysis showed a round blue cell tumor consistent with an Ewing sarcoma, and the surgical margins were tumor free. CONCLUSIONS: Retroperitoneal malignancies are rare but usually severe conditions. Our case report showed that retroperitoneal EES with renal artery invasion could be treated safely with transarterial embolization and surgery.

New developments in the pathology and molecular biology of retroperitoneal sarcomas.

Retroperitoneal sarcomas (RPS) refer to a heterogeneous group of malignancies of mesenchymal origin developing from retroperitoneal tissues and vessels. The most frequent RPS are well differentiated/dedifferentiated liposarcomas and leiomyosarcomas, but other rare histological subtypes can be observed. Over the last decade, significant advances have been made in the pathological and molecular characterization of sarcomas. These advances have led to major changes in their diagnostic management as well as in the development of new therapeutic strategies based on tumor biology and microenvironment. This review describes the current knowledge and recent findings in the pathology and molecular biology of the most frequent RPS subtypes.

Current management of benign retroperitoneal tumors.

Benign retroperitoneal tumors (BRT) represent a rare group of heterogeneous diseases. The literature lacks high-quality evidence about the optimal management of BRT, and most of the information available takes the form of case reports or case series. The aim of this review is to provide an overview of current management strategies for adult patients with BRT. A literature search using PubMed indexed articles was conducted and BRT were classified into five different biological subgroups: 1) lipomatous tumors, 2) smooth muscle tumors, 3) peripheral nerve sheath tumors, 4) myofibroblastic tumors, and 5) others. Tumors that are primarily pelvic in origin were excluded. Despite the significant heterogeneity of the disease, several generic considerations have emerged and can be applied to the management of BRT. Specifically, the risk of misdiagnosing a BRT with another pathology such as retroperitoneal sarcoma is notable. When encountered, suspected BRT should therefore be referred to a specialized sarcoma center. Multidisciplinary tumor boards, present at these centers, have a pivotal role in managing BRT. The decision of whether to offer surgery, nonsurgical treatment or a "watch-and-wait" approach should be made after multidisciplinary discussion, depending on tumor histology. Moving forward, collaborative research efforts dedicated to BRT remain crucial in gathering evidence and knowledge to further optimize patient care.

Review of diagnosis, differential diagnosis, and management of retroperitoneal lymphangioma.

Lymphatic malformation (LM) is the currently preferred term for what was previously known as lymphangioma. Retroperitoneal LMs are extremely rare, benign, cystic masses that arise from lymphatic vessels. They can be challenging to diagnose because they resemble other retroperitoneal cystic tumors. The development of treatment strategies for rare diseases, including retroperitoneal LM, requires the acquisition of new knowledge to enhance our understanding of the disease progression. Therefore, we present an update regarding fundamental and advanced issues associated with retroperitoneal LM. This review describes the epidemiology, histopathology, biomedicine, clinical manifestations, radiological features, differential diagnosis, and management of this lesion.

Landmark Series: A Review of Landmark Studies in the Treatment of Primary Localized Retroperitoneal Sarcoma.

Primary localized retroperitoneal soft tissue sarcomas (RPS) have shorter survival than other soft tissue sarcoma sites owing to higher local recurrence rates associated with histologic types most commonly found in this location, large tumor size at diagnosis (median 20 cm), and anatomical constraints of surgery in the retroperitoneum. The only curative treatment for RPS has traditionally been complete macroscopic en bloc resection with adjacent structures that cannot be surgically separated from the tumor. Compartmental resection, incorporating adjacent organs and soft tissues en bloc, even without overt infiltration at the time of surgery, performed in sarcoma referral centers may reduce local recurrence rates. Preoperative radiotherapy has not been shown to reduce early 3-year local recurrences in a phase III, international, randomized, controlled trial (STRASS). Longer follow-up is needed to determine whether well-differentiated and low-grade dedifferentiated liposarcoma prone to late local recurrences may benefit. Currently, there is no level 1 evidence to support the use of perioperative systemic therapy. Observational studies suggest that patients with high-grade histologies and borderline resectable RPS may benefit. A phase III, international, randomized, controlled trial (STRASS2) is currently evaluating a histology-tailored chemotherapy regimen for patients with leiomyosarcoma and dedifferentiated liposarcoma at high risk of distant metastatic recurrence. Novel biomarkers can help determine prognosis and more accurately predict response to treatment, but more research is needed to translate these discoveries into therapeutic benefits. Refined molecular data for histological types will allow personalized surgery, radiotherapy, and systemic therapy with lower toxicity and improved survival in the future.

Transferability of Health-Related Quality of Life Data of Large Observational Studies to Clinical Practice: Comparing Retroperitoneal Sarcoma Patients from the PROSa Study to a TARPS-WG Cohort.

INTRODUCTION: Health-related quality of life (HRQoL) is crucial for shared decision-making. The "Patient-Reported Outcome measures in Sarcoma" (PROSa) study evaluated HRQoL in general. We evaluated the transferability of PROSa data to clinical practice for the subgroup of retroperitoneal sarcoma (RPS). METHODS: To obtain a PROSa-RPS cohort, we excluded patients with bone sarcomas and gastrointestinal stromal tumors from the complete PROSa cohort (n = 1,113), limited tumor localization to trunk and retroperitoneum, and excluded patients with metastases. We evaluated the HRQoL data of the resulting 76 patients and compared their clinical data to those of the Transatlantic Autralasian Retroperitoneal Sarcoma Working Group (TARPS-WG, n = 1,007). RESULTS: Confidence intervals for patient sex, histological subtype (LPS vs. non-LPS), grading (G1 vs. G2/3), surgical margins (R2 vs. no R2), and perioperative chemo- and radiotherapy (yes vs. no) were overlapping in both cohorts. EORTC QLQ-C30 from RPS-PROSa patients demonstrated that two-thirds had clinically relevant restrictions in physical functioning. Two-thirds reported dyspnea, followed by fatigue and pain. CONCLUSION: Clinical data from RPS-PROSa patients are comparable to those of an RPS reference cohort from expert centers. We believe that HRQoL data of RPS patients extracted from PROSa are transferable to clinical practice.

Adjuvant therapy for retroperitoneal sarcoma: a meta-analysis.

BACKGROUND: Adjuvant therapy is a promising treatment to improve the prognosis of cancer patients, however, the evidence base driving recommendations for adjuvant radiotherapy (ART) or chemotherapy (ACT) in retroperitoneal sarcomas (RPS) primarily hinges on observational data. The aim of this study was to evaluate the effectiveness of adjuvant therapy in the management of RPS patients. METHODS: We searched PubMed, Web of Science, Embase, ASCO Abstracts, and Cochrane Library for comparative studies (until December 2020) of adjuvant therapy versus surgery alone. Data on the following endpoints were evaluated: overall survival (OS), local recurrence (LR), recurrence-free survival (RFS), and metastasis-free survival (MFS). Data were summarized as hazard ratios (HR) with 95% confidence intervals (CI). Risk of bias of studies was assessed with Begg's and Egger's tests. RESULTS: A total of 15 trials were eligible, including 9281 adjuvant therapy and 21,583 surgery alone cases (20 studies for OS, six studies for RFS, two studies for LR, and two studies for MFS). Meta-analysis showed that ART was associated with distinct advantages as compared to surgery alone, including a longer OS (HR = 0.80, P < 0.0001), a longer RFS (HR = 0.61, P = 0.0002), and a lower LR (HR = 0.31, P = 0.005). However, this meta-analysis failed to demonstrate a benefit of ACT for RPS patients, including OS (HR = 1.11, P = 0.19), RFS (HR = 1.30, P = 0.09) and MFS (HR = 0.69, P = 0.09). In the sensitivity analysis, ACT was associated with a worse OS (HR = 1.19, P = 0.0002). No evidence of publication bias was observed. CONCLUSIONS: Overall, the quality of the evidence was moderate for most outcomes. The evidence supports that ART achieved a generally better outcome as compared to surgery alone.

Role of Radiation Therapy for Newly Diagnosed Retroperitoneal Sarcoma.

OPINION STATEMENT: Soft tissue sarcomas (STS) are rare, aggressive, and heterogenous tumors, comprising approximately 1% of adult cancers with over 50 different subtypes. The mainstay of treatment for retroperitoneal sarcomas (RPS) includes surgical resection. The addition of radiation therapy (RT), either preoperatively or postoperatively, has been used to potentially decrease the risk of local recurrence. The recently published results from STRASS (EORTC-STBSG 62092-22092), which randomized patients to receive or not receive preoperative radiation, indicate no abdominal recurrence-free survival benefit (primary endpoint) nor overall survival benefit to date from the addition of preoperative RT prior to surgical resection in patients with RPS. Keeping in mind caveats of subgroup analyses, the data show a significant reduction in local recurrence with radiation therapy in resected patients and non-significant trends toward improved abdominal recurrence-free survival in all patients and improved local control and abdominal recurrence-free survival in patients with liposarcoma and low-grade sarcoma. Given the high rate of local failure with surgery alone, it is possible that higher RT dose and/or selective RT dose painting may improve outcomes. Prior to treatment, the authors encourage multidisciplinary review and discussion of management options at a sarcoma center for patients with RPS. Selective use of RT may be considered for patients at high risk of local recurrence.

Retroperitoneal sarcoma: the Transatlantic Australasian Retroperitoneal Sarcoma Working Group Program.

PURPOSE OF REVIEW: The Transatlantic Australasian Retroperitoneal Sarcoma Working Group (TARPSWG) is a bottom-up clinical network established in 2013 with the goal of improving the care and outcomes of patients with retroperitoneal sarcoma (RPS). Here, we review the knowledge produced by this collaborative effort and examine the future potential of this group. RECENT FINDINGS: TARPSWG has produced retrospective studies focused on patients with primary and recurrent RPS allowing a better understanding of patient prognosis, treatment outcomes and tumor biology. The group has played a pivotal role in a phase III randomized STudy of preoperative RAdiotherapy plus Surgery versus surgery alone for patients with Retroperitoneal Sarcoma (STRASS) trial, favoring patient recruitment and trial completion. A prospective registry for patients with primary RPS populated by TARPSWG members is ongoing. TARPSWG has created consensus papers with recommendations regarding the management of patients with primary, recurrent and metastatic RPS that collated the views of representatives of sarcoma centers from Europe, North America, Asia and Australia. SUMMARY: Since its inception, TARPSWG has become a leading network in the field of RPS. It has made a major contribution to the world of RPS research and cares allowing to overcome the limitations related to the rarity of the disease through collaboration.

Retroperitoneal extension of massive ulcerated testicular seminoma through the inguinal canal: A case report.

INTRODUCTION: Testicular cancers represent about 5% of all urological malignancies and 1-1.5% of all male neoplasms. Most of the testicular cancers are localized (68%) at diagnosis. Bulky masses in the scrotum are rare. We present a rare case of bulky testicular cancer with retroperitoneal spread through the inguinal canal. CASE REPORT: A 44-year-old man came to the emergency department referring weakness and the presence of a scrotal mass. At physical examination, a voluminous mass was found, with necrotic phenomena within the scrotum. Abdomen was tense and sore. Abdominal CT scan revealed a bulky testicular mass spreading to the retroperitoneal space through the inguinal canal with node enlargement. Patient underwent orchiectomy with excision of infiltrated scrotum skin. Histologic diagnosis confirmed a typical form seminoma. The patient was then treated with a cisplatin-based chemotherapy, with a partial response. The patient recently relapsed and he is being treated with a new line of chemotherapy and subsequent surgery with or without radiotherapy. CONCLUSIONS: We described a rare presentation of testicular cancer. This case highlights the importance of a multidisciplinary approach to rare testis tumour presentation and early diagnosis for testicular cancers.

Diagnostic and management challenges for MDM2-, CDK4-negative fatty tumors of the retroperitoneum.

BACKGROUND: Neoplasms of the retroperitoneum that contain a major fat component may represent either benign entities, such as lipomas or angiomyolipomas, or malignancy such as liposarcoma. Distinguishing these diagnoses has important implications for management. While liposarcomas often stain positively for MDM2 and CDK4 proteins, absence of these markers can lead to diagnostic and management challenges. METHODS: We examined three cases in our institution of fat-containing masses of the retroperitoneum that lacked MDM2 and CDK4 markers to highlight the challenges in diagnosing and managing these cases. A thorough review of the literature examining radiologic and histologic features that can be used to determine that diagnosis was conducted and summarized. RESULTS: The three cases we present represent the three main diagnostic entities that can be found in among fatty tumors of the retroperitoneum: lipoma, angiomyolipoma, and liposarcoma. While radiologic features and analysis of histology helped to inform management, these cases in conjunction with the literature also illustrate the limitations of the diagnostic work up and importance also factoring the biologic behavior of the tumor in its management. CONCLUSION: Fat-containing tumors of the retroperitoneum that do not stain for MDM2 or CDK4 can pose a diagnostic challenge. Assessing radiologic and pathologic features in conjunction with the biologic behavior of these tumors should inform their management.