Giant lipomatous tumor of the left back favoring atypical lipomatous tumor/well-differentiated liposarcoma: a case report

Abstract

Giant lipomatous tumors of the trunk are rare and can pose diagnostic and reconstructive challenges. A 71-year-old man presented with a left back mass that had enlarged over 30 years, especially during the previous 2 years. The mass measured 56 × 54 × 28 cm clinically; computed tomography and magnetic resonance imaging showed a predominantly fat-containing thoracodorsal lesion measuring 27.1 × 18.6 cm on axial images, with septa and solid nodules but no definite muscle invasion. The tumor was excised under general anesthesia with flap reconstruction and weighed 10 kg. Histology showed mature adipocytes of variable size with scattered atypical stromal cells and lipoblasts. MDM2 immunostaining was negative, and molecular confirmation was unavailable; the findings favored an atypical lipomatous tumor/well-differentiated liposarcoma after clinicopathological correlation. Recovery was uneventful, with no recurrence at 9 months. Careful imaging, complete excision when feasible, and long-term surveillance are essential.

Introduction

Atypical lipomatous tumor/well-differentiated liposarcoma (ALT/WDL) is a locally aggressive adipocytic neoplasm and represents a substantial subset of adult liposarcomas [1, 2]. Most lesions grow slowly and are painless, so diagnosis may be delayed until they become large enough to cause deformity, functional limitation, or operative difficulty. Cross-sectional imaging is central to preoperative planning because thick septa, nodular non-fatty components, and relationships to muscle and neurovascular structures help distinguish ALT/WDL from benign lipoma and guide excision [3]. Histopathology remains essential, and molecular testing for murine double minute 2 (MDM2) or cyclin-dependent kinase 4 (CDK4) amplification is often useful when morphology and immunohistochemistry are equivocal [4]. We report a giant left-back lipomatous tumor weighing 10 kg that clinically and morphologically favored ALT/WDL.

Case report

A 71-year-old man was admitted with a left back mass that had been present for 30 years and had enlarged rapidly during the previous 2 years. He had no remarkable past medical history. Examination showed a giant soft, well-circumscribed mass involving the left shoulder and back, extending from the suprascapular region to the lumbar region. The lateral borders reached the mid-axillary line and spine, and the surface showed superficial varicose veins. The clinical external size was ~56 × 54 × 28 cm (Fig. 1). No superficial lymphadenopathy was identified.

Contrast-enhanced computed tomography (CT) showed a large fat-density mass in the left thoracodorsal region, measuring 27.1 × 18.6 cm on axial images. Internal solid nodules and fibrous septa were present, and adjacent muscles were displaced without definite invasion (Fig. 2a). Thoracoabdominal magnetic resonance imaging (MRI) confirmed a predominantly fatty mass with solid nodules and fibrous strands. Imaging suggested prominent paravertebral and thoracodorsal-region feeding vessels; the exact source artery was not specified. The difference between the clinical and imaging measurements reflected external 3D measurement versus the largest axial cross-section.

Preoperative hematological tests and tumor marker levels were within normal limits. After written informed consent, the patient underwent excision under general anesthesia with flap reconstruction. A spindle-shaped incision was made over the tumor surface. The encapsulated yellow tumor was dissected layer by layer, and the feeding vessels were ligated. The tumor was removed grossly intact and weighed 10 kg (Fig. 3a). Intraoperative blood loss was ~100 ml. Formal histological margin distance was not available, so the resection is described only as grossly complete.

Histology showed a lipomatous tumor composed of mature adipocytes of variable size with scattered atypical stromal cells and lipoblasts (Fig. 2b and c). Immunohistochemistry showed partial S-100 positivity, scattered weak P16 positivity, a Ki-67 index of ~2%, and negative MDM2 immunostaining (Fig. 2d). MDM2 fluorescence in situ hybridization, CDK4 immunohistochemistry, and 12q13–15 amplification testing were not available. After clinicopathological correlation, the findings favored ALT/WDL, but the lack of molecular confirmation was considered a diagnostic limitation. The drain was removed on postoperative Day 5 and sutures on Day 14. The incision healed well. No local recurrence or distant metastasis was observed at 9 months (Fig. 3b).

Discussion

This case highlights three practical issues in managing giant superficial lipomatous tumors [5]. First, clinical size and imaging size may appear discordant when external 3D measurements are compared with the largest axial CT or MRI dimension. Reporting the measurement plane is therefore important, especially for very large deforming masses. Second, vascular mapping should be anatomically precise. In a giant thoracodorsal tumor, feeding vessels may arise from regional paravertebral, intercostal, lumbar, dorsal scapular, thoracodorsal, or other branches depending on tumor extent; a nonspecific assignment of arterial origin should be avoided unless confirmed by angiographic imaging.

Third, the diagnosis of ALT/WDL should not rely on MDM2 immunohistochemistry alone. ALT/WDL is typically composed of mature adipocytes with variation in cell size and atypical hyperchromatic stromal cells [1, 2]. MDM2 or CDK4 amplification testing can support distinction from benign lipoma and selected mimics, especially in older patients with large deep or recurrent tumors [4]. In the present case, morphology and imaging favored ALT/WDL, but negative MDM2 immunostaining and the absence of molecular testing require cautious wording. If archival tissue is available, MDM2 fluorescence in situ hybridization or equivalent 12q13–15 amplification testing would strengthen the final diagnosis.

Complete excision remains the main treatment for resectable ALT/WDL [6]. For giant superficial tumors, preoperative imaging should define the capsule, muscle invasion, and main vessels; intraoperative dissection should balance complete removal with preservation of major neurovascular structures and soft-tissue coverage. For retroperitoneal or other deep tumors, multidisciplinary planning and extended resection may be required [7]. Because margin distance was not documented here, margin status should not be described as pathologically negative. Radiotherapy is generally reserved for selected high-risk, unresectable, or margin-positive situations, and its benefit varies by anatomical site [8–10]. Conventional chemotherapy has limited value for ALT/WDL unless dedifferentiated or metastatic disease is present, while molecularly targeted approaches remain investigational or context dependent [11, 12].

Although ALT/WDL has low metastatic potential, local recurrence and dedifferentiation can occur, particularly after incomplete excision or in anatomically constrained sites [13]. This patient remained disease-free at 9 months, but longer surveillance with periodic clinical examination and imaging is needed. The key lessons are to document imaging measurements precisely, avoid overinterpreting unconfirmed vascular anatomy, acknowledge the MDM2-negative/molecularly unconfirmed diagnostic limitation, and report resection status only when pathological margin data support it. This case was reported in line with the SCARE guideline [14].

Acknowledgements

We extend our sincere gratitude to the entire surgical team and nursing staff for their valuable contributions to the successful diagnosis and treatment of this case. Finally, we appreciate the valuable insights provided by our colleagues in the Department of Pathology on the analysis of histopathological findings, and also thank our colleagues in the Department of Radiology for their valuable opinions on the analysis of imaging findings.

Author contributions

Ziling Zhang (Data curation, Writing—original draft), Teng Fan (Data curation), Qian Wang (Data curation, Formal analysis), Zhijie Zhang (Formal analysis), Xiaobo Yu (Writing—review & editing), Bin Wu (Supervision, Writing—review & editing). All authors have reviewed and approved the final manuscript and agree to be accountable for all aspects of the work.

Conflicts of interest

None declared.

Funding

None declared.

Declarations

Ethical approval was waived because this single-patient case report did not constitute human-subjects research according to institutional policy.

Written informed consent was obtained from the patient for publication of this case report and accompanying images.

Research registration was not applicable.

During manuscript preparation, the authors used ChatGPT only to improve language and readability; no AI tool was used for data collection, data analysis, image generation, or clinical decision-making. The authors reviewed and edited all AI-assisted content and take responsibility for the final manuscript.

References

Author notes