Active surveillance and emerging medical treatment options for desmoid: when and for whom?

PURPOSE OF REVIEW: This article discusses the evolving approaches to desmoid tumors management, shedding light on recent developments. RECENT FINDINGS: Active surveillance has become the primary approach for managing primary peripheral desmoid tumors. This strategy was initially based on evidence from retrospective studies. Roughly 50% of cases managed with active surveillance show spontaneous stabilization or regression. Recent prospective trials conducted in Italy, The Netherlands, and France (2022-2023) confirm the efficacy of active surveillance, revealing 3-year progression-free survival rates ranging from 53.4 to 58%. For the patients under active surveillance, decisions regarding treatment are based on significant tumor growth or progressive symptoms. Moreover, three contemporary randomized trials investigated medical treatments for progressive or recurrent desmoid tumors. Sorafenib, pazopanib, and nirogacestat demonstrated clinical activity, as evidenced by favorable progression-free survival and objective response rates. SUMMARY: Active surveillance has solidified its position as the primary management approach for desmoid tumors, validated by three robust prospective studies. Three recent randomized trials explored medical treatment for progressive or recurrent desmoid tumors, revealing promising clinical activities.

Activation of lysosomal iron triggers ferroptosis in cancer.

Iron catalyses the oxidation of lipids in biological membranes and promotes a form of cell death referred to as ferroptosis1-3. Identifying where this chemistry takes place in the cell can inform the design of drugs capable of inducing or inhibiting ferroptosis in various disease-relevant settings. Whereas genetic approaches have revealed underlying mechanisms of lipid peroxide detoxification1,4,5, small molecules can provide unparalleled spatiotemporal control of the chemistry at work6. Here, we show that the ferroptosis inhibitor liproxstatin-1 (Lip-1) exerts a protective activity by inactivating iron in lysosomes. Based on this, we designed the bifunctional compound fentomycin that targets phospholipids at the plasma membrane and activates iron in lysosomes upon endocytosis, promoting oxidative degradation of phospholipids and ferroptosis. Fentomycin effectively kills primary sarcoma and pancreatic ductal adenocarcinoma cells. It acts as a lipolysis-targeting chimera (LIPTAC), preferentially targeting iron-rich CD44high cell-subpopulations7,8 associated with the metastatic disease and drug resistance9,10. Furthermore, we demonstrate that fentomycin also depletes CD44high cells in vivo and reduces intranodal tumour growth in an immunocompetent murine model of breast cancer metastasis. These data demonstrate that lysosomal iron triggers ferroptosis and that lysosomal iron redox chemistry can be exploited for therapeutic benefits.

Technical considerations for isolated limb perfusion: A consensus paper.

BACKGROUND: Isolated limb perfusion (ILP) is a well-established surgical procedure for the administration of high dose chemotherapy to a limb for the treatment of advanced extremity malignancy. Although the technique of ILP was first described over 60 years ago, ILP is utilised in relatively few specialist centres, co-located with tertiary or quaternary cancer centres. The combination of high dose cytotoxic chemotherapy and the cytokine tumour necrosis factor alpha (TNFα), mandates leakage monitoring to prevent potentially serious systemic toxicity. Since the procedure is performed at relatively few specialist centres, an ILP working group was formed with the aim of producing technical consensus guidelines for the procedure to streamline practice and to provide guidance for new centres commencing the technique. METHODS: Between October 2021 and October 2023 a series of face to face online and hybrid meetings were held in which a modified Delphi process was used to develop a unified consensus document. After each meeting the document was modified and recirculated and then rediscussed at subsequent meeting until a greater than 90% consensus was achieved in all recommendations. RESULTS: The completed consensus document comprised 23 topics in which greater than 90% consensus was achieved, with 83% of recommendations having 100% consensus across all members of the working group. The consensus recommendations covered all areas of the surgical procedure including pre-operative assessment, drug dosing and administration, perfusion parameters, hyperthermia, leakage monitoring and theatre logistics, practical surgical strategies and also post-operative care, response evaluation and staff training. CONCLUSION: We present the first joint expert-based consensus statement with respect to the technical aspects of ILP that can serve as a reference point for both existing and new centres in providing ILP.

Handling missing covariates in observational studies: an illustration with the assessment of prognostic factors of survival outcomes in soft-tissue or visceral sarcomas in irradiated fields (SIF).

Background: Missing covariates are common in observational research and can lead to bias and loss of statistical power. Limited data regarding prognostic factors of survival outcomes of sarcomas in irradiated fields (SIF) are available. Because of the long lag time between irradiation of first cancer and scarcity of SIF, missing data are a critical issue when analyzing long-term outcomes. We assessed prognostic factors of overall (OS), progression-free (PFS), and metastatic-progression-free (MPFS) survivals in SIF using three methods to account for missing covariates. Methods: We relied on the NETSARC French Sarcoma Group database, Cox (OS/PFS), and competitive hazards (MPFS) survival models. Covariates investigated were age, sex, histological subtype, tumor size, depth and grade, metastasis, surgery, surgical resection, surgeon's expertise, imaging, and neo-adjuvant treatment. We first applied multiple imputation (MI): observed data were used to estimate the missing covariate. With the missing-data modality approach, a category missing was created for qualitative variables. With the complete-case (CC) approach, analysis was restricted to patients without missing covariates. Results: CC subjects (N = 167; 33%) presented more often with soft-tissue sarcoma (versus visceral sarcoma) and grade I-II tumors as compared to the 504 eligible cases. With MI (N = 504), factors associated with the worst outcome included metastasis (p = 0.04) and R1/R2 resection (p < 0.001) for OS; higher grade/non-gradable tumors (p = 0.002) and R1/R2 resection (p < 0.001) for PFS; and metastasis (p = 0.01) for M-PFS. The 'missing-data modality' approach (N = 504) led to different associations, including significance reached due to variables with the modality 'missing'. The CC analysis led to different results and reduced precision. Conclusion: The CC population was not representative of the eligible population, introducing bias, in addition to worst precision. The 'missing-data modality method' results in biased estimates in non-randomized studies, as outcomes may be related to variables with missing values. Appropriate statistical methods for missing covariates, for example, MI, should therefore be considered.

Diagnostic accuracy and safety of percutaneous core needle biopsy of retroperitoneal tumours.

BACKGROUND: Histologic subtype of cancer guides treatment sequencing and the extent of surgery for retroperitoneal tumours (RPTs) but concerns persist regarding percutaneous core needle biopsy (CNB). OBJECTIVE: Endpoints were the incidence of early complications, needle tract seeding (NTS) after CNB, diagnostic accuracy. METHODS: Between 2015 and 2022, data from patients with RPT who underwent a CNB and who operated on at Institut Curie were collected. We retrospectively reviewed the medical records and microscopic analysis of both CNB and surgical specimens to evaluate the diagnostic accuracy of CNB (quantified using positive and negative predictive values, PPV/NPV). RESULTS: 313 patients underwent CNB. In 10/326 (3 %) procedures, minor complications were observed. One of 212 (0.47 %) resected RPSs exhibited a local recurrence compatible with NTS. Microscopic analysis of CNB specimens allowed the classification of tumours between groups of cancers and benign/intermediate mesenchymal tumours in 307/313 (98 %) patients. Among the 204 patients with retroperitoneal sarcoma, the overall concordance between CNB and final pathology following resection was 178/204 (87.2 %). The respective PPVs of solitary fibrous tumour, dedifferentiated liposarcoma, leiomyosarcoma and well-differentiated liposarcoma were 100 %, 98 %, 97 % and 68 %, respectively. The diagnosis of a high-grade (G 2-3) sarcoma resulted in a high specificity (97 %) and PPV (98 %) but low sensitivity (76 %). CONCLUSIONS: CNB allowed the classification of RPT in the vast majority of patients with a low morbidity rate. Concordance with final diagnosis was high for sarcomas with the exception of well-differentiated liposarcoma. As a result, CNB results should be integrated with imaging/radiomics by multidisciplinary tumour boards.

New Sarculator Prognostic Nomograms for Patients With Primary Retroperitoneal Sarcoma: Case Volume Does Matter.

OBJECTIVE: To update the current Sarculator retroperitoneal sarcoma (RPS) prognostic nomograms considering the improvement in patient prognosis and the case volume effect. BACKGROUND: Survival of patients with primary RPS has been increasing over time, and the volume-outcome relationship has been well recognized. Nevertheless, the specific impact on prognostic nomograms is unknown. METHODS: All consecutive adult patients with primary localized RPS treated at 8 European and North American sarcoma reference centers between 2010 and 2017 were included. Patients were divided into 2 groups: high-volume centers (HVC, ≥13 cases/year) and low-volume centers (LVC, <13 cases/year). Primary end points were overall survival (OS) and disease-free survival (DFS). Multivariable analyses for OS and DFS were performed. The nomograms were updated by recalibration. Nomograms performance was assessed in terms of discrimination (Harrell C index) and calibration (calibration plot). RESULTS: The HVC and LVC groups comprised 857 and 244 patients, respectively. The median annual primary RPS case volume (interquartile range) was 24.0 in HVC (15.0-41.3) and 9.0 in LVC (1.8-10.3). Five-year OS was 71.4% (95% CI: 68.3%-74.7%) in the HVC cohort and 63.3% (56.8%-70.5%) in the LVC cohort ( P =0.012). Case volume was associated with both OS (LVC vs. HVC hazard ratio 1.40, 95% CI: 1.08-1.82, P =0.011) and DFS (hazard ratio 1.93, 95% CI: 1.57-2.37, P <0.001) at multivariable analyses. When applied to the study cohorts, the Sarculator nomograms showed good discrimination (Harrell C index between 0.68 and 0.73). The recalibrated nomograms showed good calibration in the HVC group, whereas the original nomograms showed good calibration in the LVC group. CONCLUSIONS: New nomograms for patients with primary RPS treated with surgery at high-volume versus low-volume sarcoma reference centers are available in the Sarculator app.

Impact of guideline adherence and expert center referral on the early management and outcomes of uterine sarcoma patients: A retrospective analysis from the French NETSARC network.

OBJECTIVE: Uterine sarcomas are rare tumors with a poor prognosis. Their diagnosis is often incidental, following surgery. Our goal was to examine the early management strategies for uterine sarcomas, and to assess the impact of guideline adherence and expert center referral on both the management approaches and the clinical outcomes in patients with uterine sarcomas. METHODS: We retrospectively analyzed medical records from patients with uterine sarcoma referred to the Institut Curie and registered in the database of the French NETSARC network. RESULTS: In total, 100 patients, with a median age of 54 years, were included in the analyses. On MRI scans (n = 36), all patients had at least two signs suggestive of malignancy, and 77.8 % had four or more signs. No preoperative biopsy was performed in 65.6 % of cases. Only 14.1 % of patients underwent initial surgery at an expert center. Surgery performed outside the network was significantly associated with morcellation (32.9 % vs. 0 %; p = 0.036), fewer negative margins (R0 margins 52.4 % vs. 100 %; p = 0.006), and poor adherence to surgical guidelines (28.3 vs. 72.7 %; p = 0.013). Multivariate analysis showed that non-adherence to surgical recommendations was not significantly associated with relapse-free survival (HR = 0.54; 95 % CI [0.21-1.38]), but was an independent predictor of poor overall survival (HR = 0.12; 95 % CI [0.03-0.52]; p = 0.005). CONCLUSION: Despite a high frequency of suspicious clinical and radiological signs, a large proportion of women undergoing sarcoma surgery are treated outside of expert networks. We provide guidelines, integrating the clinical context and radiological signs to encourage early referral to reference centers for sarcoma.

What is the optimal (neo)adjuvant strategy of extremity high-risk soft tissue sarcomas (ESTS)?

Currently, the standard treatment for extremity high-risk soft tissue sarcomas (ESTS) combines surgery and pre- or post-op radiation therapy (RT). In some selected cases, chemotherapy (CT) is incorporated into the therapeutic algorithm as a neoadjuvant approach to enable conservative management. Given the risk of local or metastatic relapse, this paper discusses the potential benefits of CT and RT in high-grade ESTs. The role of adjuvant chemotherapy in addition to neoadjuvant CT, the prognostic value of the pathological response to neoadjuvant treatment, and the role for an adjuvant "boost" following resection after pre-operative radiotherapy will be discussed.

A CT-based radiomics classification model for the prediction of histological type and tumour grade in retroperitoneal sarcoma (RADSARC-R): a retrospective multicohort analysis.

BACKGROUND: Retroperitoneal sarcomas are tumours with a poor prognosis. Upfront characterisation of the tumour is difficult, and under-grading is common. Radiomics has the potential to non-invasively characterise the so-called radiological phenotype of tumours. We aimed to develop and independently validate a CT-based radiomics classification model for the prediction of histological type and grade in retroperitoneal leiomyosarcoma and liposarcoma. METHODS: A retrospective discovery cohort was collated at our centre (Royal Marsden Hospital, London, UK) and an independent validation cohort comprising patients recruited in the phase 3 STRASS study of neoadjuvant radiotherapy in retroperitoneal sarcoma. Patients aged older than 18 years with confirmed primary leiomyosarcoma or liposarcoma proceeding to surgical resection with available contrast-enhanced CT scans were included. Using the discovery dataset, a CT-based radiomics workflow was developed, including manual delineation, sub-segmentation, feature extraction, and predictive model building. Separate probabilistic classifiers for the prediction of histological type and low versus intermediate or high grade tumour types were built and tested. Independent validation was then performed. The primary objective of the study was to develop radiomic classification models for the prediction of retroperitoneal leiomyosarcoma and liposarcoma type and histological grade. FINDINGS: 170 patients recruited between Oct 30, 2016, and Dec 23, 2020, were eligible in the discovery cohort and 89 patients recruited between Jan 18, 2012, and April 10, 2017, were eligible in the validation cohort. In the discovery cohort, the median age was 63 years (range 27-89), with 83 (49%) female and 87 (51%) male patients. In the validation cohort, median age was 59 years (range 33-77), with 46 (52%) female and 43 (48%) male patients. The highest performing model for the prediction of histological type had an area under the receiver operator curve (AUROC) of 0·928 on validation, based on a feature set of radiomics and approximate radiomic volume fraction. The highest performing model for the prediction of histological grade had an AUROC of 0·882 on validation, based on a radiomics feature set. INTERPRETATION: Our validated radiomics model can predict the histological type and grade of retroperitoneal sarcomas with excellent performance. This could have important implications for improving diagnosis and risk stratification in retroperitoneal sarcomas. FUNDING: Wellcome Trust, European Organisation for Research and Treatment of Cancer-Soft Tissue and Bone Sarcoma Group, the National Institutes for Health, and the National Institute for Health and Care Research Biomedical Research Centre at The Royal Marsden NHS Foundation Trust and The Institute of Cancer Research.

Initial Active Surveillance Strategy for Patients with Peripheral Sporadic Primary Desmoid-Type Fibromatosis: A Multicentric Phase II Observational Trial.

BACKGROUND: Stabilization or spontaneous regressions are demonstrated in more than half of patients affected by primary desmoid-type fibromatosis (DF) in retrospective studies. The objective of this phase II study was to prospectively assess the behavior of primary sporadic DT managed by active surveillance (AS). METHODS: This prospective, multicenter, observational study (NCT01801176) included patients ≥18 years of age with primary sporadic DF located in an extremity or the abdominal/thoracic wall. At inclusion, all patients were initially placed on AS. Follow-up was based on clinical and radiological evaluation by magnetic resonance imaging (MRI) performed at 1, 3, 6, 9, and 12 months, and then every 6 months for 3 years. The primary endpoint was progression-free survival (PFS) at 3 years according to Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1, as evaluated by a Central Review Board. RESULTS: Between 2012 and 2015, 100 patients were enrolled. The female/male ratio was 8 and the median age was 34 years (interquartile range [IQR] 30.8-43.9). Median follow-up was 46.6 months (IQR 36.8-61.1) and the 3-year PFS was 53.4% (95% confidence interval 43.5-63.1%). At progression (48 patients), 23 patients received active treatment. Fifty-eight patients (58%) presented with spontaneous tumor regression (decrease > 0% compared with the initial size) during the first 3 months (n = 35, 35%) or after an initial progression (n = 23, 23%), of whom 26 (26%) had partial responses (PRs). The median time to PR was 31.7 months (25.3-not available). CONCLUSIONS: These data support the use of AS as the primary approach to select patients with peripheral DF who require aggressive treatment.

Significant Predictors of Postoperative Morbidity After Radical Resection of Retroperitoneal Sarcoma in a Tertiary Center.

BACKGROUND: The safety of multivisceral resection of retroperitoneal sarcoma is an issue. Previous reports have investigated its associations with the pattern of resection and factors recognized mostly per operatively. METHODS: All consecutive RPS resections from May 2015 to April 2022 were studied retrospectively with respect to adverse events. Two univariate and multivariate logistic regression analyses were performed to investigate the associations between severe adverse events and factors recognized pre- and per operatively. Associations of adverse events with overall survival (OS) and local recurrence (LR) were investigated. RESULTS: A total of 265 surgical interventions corresponding to 251 patients were recorded (38 RPS surgeries/year). Severe postoperative adverse events (Clavien-Dindo ≥ 3) occurred in 50 patients (18.9%), 15 (5.6%) patients underwent an iterative laparotomy, and 6 patients (2.3%) died within 90 days. On multivariate analysis including all parameters known preoperatively, male sex, performance status, dedifferentiated liposarcoma histology, and low serum albumin level were found to be significant predictors of major complications, whereas the timing of surgery and preoperative treatment were not. On univariate analysis including all per operative parameters, transfusion requirement, operative time, number of digestive anastomoses, and pancreas and/or major arterial resection were found to entail higher operative risk. On multivariate analysis, only transfusion requirement was significant. There was no impact of postoperative adverse events on OS or LR. CONCLUSIONS: The recognition of preoperative parameters that impact safety could mitigate the extent of the surgery, specifically the resection of adherent organs not overtly invaded. For the best decision, this surgery should be performed in referral centers.

[Uterine leiomyosarcoma - French guidelines from the GSF/NETSARC and TMRG groups]. / Léiomyosarcomes utérins ­ Référentiel de prise en charge du GSF-GETO/NETSARC+ et du groupe TMRG.

Uterine leiomyosarcomas represent the most common uterine sarcomas. The prognosis is poor with metastatic recurrence in more than half of the cases. The purpose of this review is to make French recommendations for the management of uterine leiomyosarcomas within the framework of the French Sarcoma Group - Bone Tumor Study Group (GSF-GETO)/NETSARC+ and Malignant Rare Gynecological Tumors (TMRG) networks in order to optimize their therapeutic management. The initial assessment includes a MRI with diffusion perfusion sequence. The diagnosis is histological with a review in an expert center (Reference Network in Sarcoma Pathology (RRePS)). Total hysterectomy with bilateral salpingectomy, en bloc without morcellation, is performed when complete resection is possible, whatever the stage. There is no indication of systematic lymph node dissection. Bilateral oophorectomy is indicated in peri-menopausal or menopausal women. Adjuvant external radiotherapy is not a standard. Adjuvant chemotherapy is not a standard. It can be an option and consists in doxorobucin based protocols. In the event of local recurrence, the therapeutic options are based on revision surgery and/or radiotherapy. Systemic treatment with chemotherapy is most often indicated. In case of metastatic disease, surgical treatment remains indicated when resecable. In cases of oligo-metastatic disease, focal treatment of metastases should be considered. In the case of stage IV, chemotherapy is indicated, and is based on first-line doxorubicin-based protocols. In the event of excessive deterioration in general condition, management by exclusive supportive care is recommended. External palliative radiotherapy can be proposed for symptomatic purposes.

Prognostic factors and outcomes of adult spermatic cord sarcoma. A study from the French Sarcoma Group.

PURPOSE: To evaluate the outcomes of adult patients with spermatic cord sarcoma (SCS). METHODS: All consecutive patients with SCS managed by the French Sarcoma Group from 1980 to 2017 were analysed retrospectively. Multivariate analysis (MVA) was used to identify independent correlates of overall survival (OS), metastasis-free survival (MFS), and local relapse-free survival (LRFS). RESULTS: A total of 224 patients were recorded. The median age was 65.1 years. Forty-one (20.1%) SCSs were discovered unexpectedly during inguinal hernia surgery. The most common subtypes were liposarcoma (LPS) (73%) and leiomyosarcoma (LMS) (12.5%). The initial treatment was surgery for 218 (97.3%) patients. Forty-two patients (18.8%) received radiotherapy, 17 patients (7.6%) received chemotherapy. The median follow-up was 5.1 years. The median OS was 13.9 years. In MVA, OS decreased significantly with histology (HR, well-differentiated LPS versus others = 0.096; p = 0.0224), high grade (HR, 3 versus 1-2 = 2.7; p = 0.0111), previous cancer and metastasis at diagnosis (HR = 6.8; p = 0.0006). The five-year MFS was 85.9% [95% CI: 79.3-90.6]. In MVA, significant factors associated with MFS were LMS subtype (HR = 4.517; p < 10-4) and grade 3 (HR = 3.664; p < 10-3). The five-year LRFS survival rate was 67.9% [95% CI: 59.6-74.9]. In MVA, significant factors associated with local relapse were margins and wide reresection (WRR) after incomplete resection. OS was not significantly different between patients with initial R0/R1 resection and R2 patients who underwent WRR. CONCLUSIONS: Unplanned surgery affected 20.1% of SCSs. A nonreducible painless inguinal lump should suggest a sarcoma. WRR with R0 resection achieved similar OS to patients with correct surgery upfront.

[Endometrial stromal sarcoma: French Guidelines from the French Sarcoma Group and the Rare Malignant Gynecologic Tumors Group]. / Sarcomes du stroma endométrial de bas grade : référentiels de prise en charge du GSF-GETO/NETSARC+ et du groupe TMRG.

Low-grade endometrial stromal sarcoma (LG-ESS) accounts for approximately 15% of all uterine sarcomas. Median age of patients is around 50 years and half of the patients are premenopausal. In all, 60% of cases present with FIGO stage I disease. Preoperatively radiologic findings of ESS are not specific. Pathological diagnosis remains essential. This review aimed to present the French guidelines for low grade ESS treatment within the Groupe sarcome français - Groupe d'étude des tumeurs osseuse (GSF-GETO)/NETSARC+ and tumeur maligne rare gynécologique (TMRG) networks. Treatments should be validated in multidisciplinary team involved in sarcomas or rare gynecologic tumors. Hysterectomy is the cornerstone of treatment for localized ESS, and morcellation should be avoided. Systematic lymphadenectomy in ESS does not improve the outcome and is not recommended. Leaving the ovaries in situ in stage I tumors could be discussed for young women. Adjuvant hormonal treatment could be considered, for two years for stage I with morcellation or stage II and livelong for stages III or IV. Nevertheless, several questions remain, such as optimal doses, regimens (progestins or aromatase inhibitors) and duration of therapy. Tamoxifen is contraindicated. Secondary cytoreductive surgery if feasible for recurrent disease, appears to be an acceptable approach. Systemic treatment for recurrent or metastatic disease is mainly hormonal, with or without surgery.

Pain in desmoid-type fibromatosis: Prevalence, determinants and prognosis value.

The aim of this study is to evaluate the prevalence, determinants and prognostic value of pain at diagnosis in patients with desmoid-type fibromatosis (DF). We selected patients from the ALTITUDES cohort (NCT02867033), managed by surgery, active surveillance or systemic treatments, with pain assessment at diagnosis. Patients were invited to fill QLQ-C30 questionnaire and Hospital Anxiety Depression Scale. Determinants were identified using logistic models. Prognostic value on event-free survival (EFS) was evaluated using the Cox model. Overall, 382 patients were included in the current study (median age: 40.2 years; 117 men). The prevalence of pain was 36%, without significant difference according to first-line treatment (P = .18). In the multivariate analysis, pain was significantly associated with tumor size >50 mm (P = .013) and tumor site (P < .001); pain was more frequent in the neck and shoulder locations (odds ratio: 3.05 [1.27-7.29]). Pain at baseline was significantly associated with poor quality of life (P < .001), depression (P = .02), lower performance status (P = .03) and functional impairment (P = .001); we also observed a nonsignificant association with anxiety (P = .10). In the univariate analysis, baseline pain was associated with poor EFS; the 3-year EFS was 54% in patients with pain compared to 72% in those without pain. After adjustment for sex, age, size and line of treatment, pain was still associated with poor EFS (hazard ratio: 1.82 [1.23-2.68], P = .003). One third of recently diagnosed patients with DF experienced pain, especially those with larger tumors and neck/shoulder locations. Pain was associated with unfavorable EFS after adjustment for the confounders.

MDM4 amplification in atypical lipomatous tumors/well-differentiated liposarcoma: Private event or alternative oncogenic mechanism?

Adipocytic tumors are the most common mesenchymal tumors in soft tissues. Among them, a diagnostic challenge relies in the distinction between lipoma and atypical lipomatous tumor (ALT)/well differentiated liposarcoma (WDLPS), as both entities are often undistinguishable not only from a radiological point of view, but also at the microscopic level and particularly when dealing with small tumor specimen. Thus, detection of recurrent MDM2 amplifications may be the only criteria to discriminate malignant tumors from lipomas. In this study, we report the case of a patient diagnosed with a well differentiated, adipocytic tumor located in the inferior limb and lacking MDM2 amplification, whose diagnosis was reclassified for ALT/WDLPS after identification of an alternative MDM4 amplification by comparative genomic hybridization profiling, whole exome sequencing and fluorescence in situ hybridization (FISH). Screening of a cohort of 37 large, deep-seated, well-differentiated adipocytic tumors previously classified as lipomas using RT-qPCR and FISH failed to detect other cases of MDM4-amplified ALT/WDLPS. This report shows that MDM4 amplification is an exceptional molecular event alternative to MDM2 amplification in ALT/WDLPS. This alteration should be considered and looked for in suspicious adipocytic tumors to optimize their surgical management.