The story began one year before the patient’s admission, when he incidentally noticed a fist-sized mass on his right back. The mass enlarged significantly over the following six months and became mildly tender to the touch. An outside hospital had offered only a presumptive diagnosis of lipoma, and no treatment was given. By the time he reached the Grade-A tertiary hospital in Zhuhai in 2024, imaging told a more complicated story. A non-contrast magnetic resonance imaging scan of the chest and back soft tissues revealed a mass measuring approximately 176 by 99 by 202 millimeters in the subcutaneous area of the posterolateral right scapula. On T1-weighted imaging the lesion showed predominantly hyperintense signals, consistent with fat, which decreased on fat-suppressed sequences and showed no signal attenuation on opposed-phase images. Within the mass, multiple T1-hypointense nodules, patchy areas, and linearations were visible, appearing hyperintense on fat-suppressed T1- and T2-weighted imaging. The largest nodule measured about 28 by 13 millimeters with distinct boundaries, and the adjacent latissimus dorsi muscle showed abnormal morphology.

Before surgery, the team performed an ultrasound-guided core needle biopsy of the right shoulder and back region. Under the microscope, that biopsy revealed adipose tissue without obvious cellular atypia, suggesting an adipocytic tumor but leaving open the critical question of whether it was a simple lipoma or an atypical lipomatous tumor/well-differentiated liposarcoma, a distinction that needle biopsies alone often cannot resolve. The surgical team proceeded with an extended excision under general anesthesia, making a longitudinal fusiform incision of approximately 20 centimeters along the right posterior axillary line. The tumor was exposed by dissecting the planes of the tumor capsule, the latissimus dorsi, serratus anterior, teres major, and teres minor muscles layer by layer. Intraoperatively, the surgeons found the tumor had a broad base, indistinct boundaries, infiltration into surrounding tissues, and a tendency to extend toward the axilla. The extended excision removed the tumor completely along with portions of the latissimus dorsi and serratus anterior muscles.

The gross specimen was a grayish-yellow mass measuring 20 by 17 by 6 centimeters, sectioned in a book-like manner, with a fusiform strip of skin measuring 16 by 6.5 centimeters attached to one side. The tumor surface appeared encapsulated, but the cut surface was grayish-yellow and soft to locally medium in texture, with no apparent grayish-white areas, and its boundary with the striated muscle was ill-defined. Part of the tumor resembled yellow-white adipose tissue, while other areas presented a cord-like, multiloculated structure. Under the microscope, the tumor was composed of fibrous and myxoid stroma containing mildly to moderately atypical spindle cells, along with varying proportions of adipocytes, lipoblasts, and floret-like multinucleated giant cells, the characteristic cellular constellation of ASPLT.

Immunohistochemistry, the technique that uses antibodies to detect specific proteins in tissue sections, added crucial pieces to the puzzle. The tumor cells were positive for CD34, with focal positivity for S-100, MDM2, Desmin, P16, and a Ki67 proliferation index of approximately 1 percent. The cells were negative for CDK4, MyoD1, beta-Catenin, ALK, SMA, and HMB45, and demonstrated a loss of expression for the retinoblastoma protein, RB1. That RB1 loss is a molecular signature found in roughly 50 to 70 percent of ASPLT cases, according to the literature reviewed by the authors, and it drives the atypical cellular proliferation and pleomorphic morphology that give these tumors their worrisome appearance. It firmly places ASPLT within the RB1-deleted tumor family rather than a sarcomatous lineage.

The decisive test, however, was fluorescence in situ hybridization, or FISH, a molecular technique that uses fluorescently labeled DNA probes to detect specific genetic changes in cells. Based on a count of 100 cells, the number of red and green signals were 249 and 241 respectively, yielding an MDM2/CEP12 ratio of 1.03. That ratio indicated no amplification of the MDM2 gene, and this absence is the paramount diagnostic criterion separating ASPLT from atypical lipomatous tumor/well-differentiated liposarcoma, which is typically characterized by amplification of the MDM2 and CDK4 genes. While MDM2 or CDK4 may display focal weak positivity on immunohistochemistry in ASPLT, they are not co-expressed, and the definitive absence of MDM2 amplification clarifies the molecular basis of the diagnosis. Integrating histomorphology, immunohistochemistry, and FISH allowed the team to identify the lesion as an adipocytic tumor with no obvious local capsule and focal involvement of striated muscle, consistent with ASPLT.

The classification of this entity has evolved considerably. ASPLT was initially reported by Dei Tos and colleagues and was historically regarded as a morphological subtype of well-differentiated liposarcoma. The fifth edition of the World Health Organization Classification of Soft Tissue and Bone Tumours, published in 2020, explicitly defined it as a benign adipocytic tumor and confirmed that atypical spindle cell lipomatous tumor and atypical pleomorphic lipomatous tumor belong to the same disease spectrum. The age of onset ranges from 6 to 87 years, peaking between 50 and 60, with a slight male predominance. The tumor most frequently affects the extremities, thighs, shoulders, and back, and rarely the head and neck or retroperitoneum. Its defining hallmark is a consistently indolent biological behavior despite concerning morphological atypia, with poorly defined borders, an absence of a true capsule, and highly variable proportions of atypical spindle cells, adipocytes, lipoblasts, and multinucleated giant cells embedded within a fibrous or myxoid stroma.

Differential diagnosis remains the central clinical challenge. Beyond well-differentiated liposarcoma, ASPLT must be distinguished from spindle cell lipoma, a benign lesion composed of uniform spindle cells admixed with mature adipocytes that is diffusely positive for CD34; ASPLT presents with a more complex pleomorphic cellular morphology and an infiltrative growth pattern, although the two share RB1 loss as a common pathophysiological link. Diffuse neurofibroma generally demonstrates diffuse S100 positivity, whereas S100 expression in ASPLT can be negative or only weakly positive, and its cellular morphology features pleomorphic cells and lipoblasts rather than uniform spindle cells. Mammary-type myofibroblastoma, composed primarily of uniform myofibroblasts and collagenous stroma with desmin positivity, lacks the pleomorphic cells and distinctive adipocytic atypia seen in ASPLT. The authors also point to the tumor microenvironment as a biological context: factors such as progranulin, described as proangiogenic agents in visceral adipose tissue, participate in tissue remodeling, localized inflammation, and cellular proliferation, and similar proangiogenic and inflammatory remodeling factors likely mediate the fibrous changes, myxoid alterations, and infiltrative growth patterns observed in these adipocytic neoplasms.

Management of ASPLT centers on complete surgical excision, the cornerstone of treatment. Because of its infiltrative growth, the local recurrence rate is documented at approximately 10 to 15 percent, strongly correlated with positive or narrow surgical margins. Despite this tendency for local recurrence, the long-term prognosis remains excellent, with virtually no documented cases of distant metastasis. In this case, the patient was followed for 18 months postoperatively with no evidence of tumor recurrence or metastasis, though the authors acknowledge that an 18-month follow-up is relatively limited and that continued clinical surveillance remains of paramount importance given the tumor’s subtle infiltrative capability and clinicopathological heterogeneity. The case’s broader message is clear: when a fatty-appearing mass shows atypical spindle cells, lipoblasts, or floret-like giant cells, morphology alone can mislead clinicians into over-diagnosis, and only the combined weight of histology, immunohistochemistry, and FISH can reliably separate this benign entity from its malignant mimic, sparing patients the morbidity of unnecessarily aggressive interventions.

Subject of Research: Diagnosis of atypical spindle cell/pleomorphic lipomatous tumor using histology, immunohistochemistry, and FISH

Article Title: Clinicopathological features and differential diagnosis of a case report of atypical spindle cell/pleomorphic lipomatous tumor

Article References: Wang, C., Jiang, Y., Liu, Q., & Wang, Y. (2026). Clinicopathological features and differential diagnosis of a case report of atypical spindle cell/pleomorphic lipomatous tumor. Frontiers in Musculoskeletal Disorders, 4, Article 1922243. https://doi.org/10.3389/fmscd.2026.1922243

Image Credits: AI Generated

DOI: 10.3389/fmscd.2026.1922243

Keywords: atypical spindle cell/pleomorphic lipomatous tumor, ASPLT, well-differentiated liposarcoma, MDM2 amplification, FISH, RB1 loss, immunohistochemistry, soft tissue tumor, WHO classification, lipomatous neoplasm, case report, surgical excision

The research, conducted at a single German center and published in CVIR Oncology, followed 13 consecutive patients who underwent percutaneous CT-guided cryoablation of histologically confirmed desmoid tumors between January 2019 and December 2024. Most were young women with tumors embedded in the rectus abdominis muscle of the abdominal wall, the classic setting for this rare disease, which strikes roughly two to four people per million each year. Twelve of the thirteen had already failed at least one line of systemic therapy, ranging from nonsteroidal anti-inflammatory drugs and hormonal agents to chemotherapy and, in one case, a gamma-secretase inhibitor.

Cryoablation destroys tissue by cycling it between extreme cold and thaw. In this study, interventional radiologists placed between 2 and 16 thin cryoprobes directly into each tumor under CT fluoroscopic guidance while the patient was under general anesthesia. A standardized double freeze-thaw protocol followed: two ten-minute freeze cycles separated by passive and active thawing phases. During each freeze, the growing ice ball is visible on CT as a sharply defined dark region, a unique advantage of cryoablation over heat-based ablation techniques, allowing operators to watch the lethal zone expand in real time and confirm it covers the tumor with at least a five-millimeter margin.

The critical technical challenge lies in what surrounds these tumors. Because most desmoids in this cohort sat in the abdominal wall, the bowel loops immediately behind the target were the structures most at risk of catastrophic freeze injury. The team deployed protective dissection techniques in 76.9 percent of procedures: hydrodissection with 5 percent dextrose solution in just over half the cases, CO₂ pneumodissection in two patients, and air dissection in one. In laparoscopically assisted cases, surgeons created capnoperitoneum and directly observed the ice ball from inside the peritoneal cavity, retracting probes by pre-planned distances between freeze cycles to sculpt an enlarged zone of destruction. Every patient’s skin was protected with injected fluid and a warm saline-filled glove.

What distinguishes this study from earlier cryoablation series is its measurement strategy. Rather than tracking overall tumor diameter with standard RECIST criteria, the investigators systematically quantified the enhancing tumor volume on contrast-enhanced MRI, using the ellipsoid formula to calculate viable, cellular tissue separately from the non-enhancing fibrotic residue that persists long after successful ablation. This distinction proved dramatic. At a median follow-up of 14.5 months, median viable tumor volume collapsed from 70.5 cubic centimeters to just 1.97 cubic centimeters, a 98.3 percent reduction with a large statistical effect size. Yet the median entire lesion volume remained 6.7 cubic centimeters, and in the most striking individual case a patient retained a 251-cubic-centimeter residual mass of which less than 2 percent was living tissue.

That discrepancy carries a direct clinical warning. Conventional size-based response criteria, which measure the whole lesion including dead fibrotic tissue, would classify many of these successfully treated patients as having only stable or partial disease, badly underestimating how thoroughly the tumor had been devitalized. Applying modified RECIST criteria, which evaluate only the enhancing component, the authors found six of twelve evaluable patients achieved complete response and six achieved partial response, for an objective response rate of 100 percent. No patient showed progression during follow-up.

Objective MRI signal analysis corroborated the volumetric findings. The T2 contrast-to-noise ratio, a quantitative measure of how brightly tumor tissue stands out from background noise on T2-weighted images, fell from a median of 146.9 at baseline to 19.5 at last follow-up, reflecting replacement of highly cellular tumor by avascular fibrosis and coagulative necrosis. T2 signal intensity relative to muscle also dropped significantly. These quantitative markers align with prior work showing that intermediate T2 signal combined with nodularity and enhancement predicts post-ablation growth, offering clinicians measurable indicators of durable local control.

Patients themselves reported substantial benefit: twelve of thirteen described improved symptoms. The safety record, however, was not flawless. One patient, notably the only one treated without any prior therapy, suffered a severe grade 3b complication after the protective dissection was discontinued at cryoprobe retrieval before the ice ball had fully thawed. The residual ice contacted adjacent bowel and skin, causing bowel wall necrosis, cutaneous frostbite, and an enterocutaneous fistula requiring surgical repair; the patient was lost to follow-up. The remaining twelve patients experienced no complications at all, and the overall 7.7 percent major complication rate sits within the 0 to 17 percent range reported across published desmoid cryoablation series.

The results compare favorably with landmark studies. The prospective CRYODESMO-01 trial reported an 86 percent nonprogression rate at twelve months and a 79 percent objective response rate, while a ten-year pediatric and young adult series documented symptom improvement in 90 percent of patients but tumor volume reductions exceeding 75 percent in only 43 percent. The authors caution that their exceptional figures likely reflect selection bias and the small sample size, and that a median follow-up of 14.5 months cannot capture recurrences appearing years later.

Nevertheless, the study delivers a clear message for the multidisciplinary management of desmoid tumors. Cryoablation, positioned as a second- or third-line option after systemic therapy fails, achieves near-complete elimination of viable tumor with meaningful symptom relief and objective, quantitative MRI evidence of tumor death. The practical implication for radiologists and oncologists alike is to differentiate viable from total lesion volume when interpreting post-ablation imaging: large areas of residual non-enhancing tissue should never be mistaken for treatment failure. Larger prospective trials with patient-reported outcomes and extended follow-up are now needed to cement enhancing volume-based assessment as the standard endpoint for this increasingly credible, minimally invasive treatment.

The biology underlying desmoid tumors helps explain why local destruction can be so effective despite the tumors’ infiltrative habits. Most sporadic cases harbor activating mutations in the CTNNB1 gene, which stabilizes beta-catenin and drives the Wnt signaling pathway that fuels fibroblast proliferation. A minority arise in patients with familial adenomatous polyposis, where germline APC mutations set the stage. Because these tumors rarely metastasize, controlling the local disease is essentially controlling the whole disease, which is why a technique that devitalizes the entire enhancing component can translate into durable clinical benefit.

The demographic pattern of the disease also deserves emphasis. Desmoid tumors show a striking predilection for young women, and pregnancy and the postpartum period are recognized risk factors, with estrogen thought to modulate tumor behavior in at least a subset of patients. This means many patients face decades of life ahead of them at diagnosis, making the avoidance of radical surgery with its high recurrence rates and functional morbidity particularly consequential. An abdominal wall tumor in a woman of childbearing age, for example, can compromise core strength, posture, and future pregnancies if treated with wide resection, whereas a percutaneous needle-based approach preserves the muscle envelope even if some fibrotic residue remains.

The shift toward active surveillance as a first step deserves further context. Longitudinal observational cohorts have shown that a substantial fraction of desmoid tumors, in some series approaching half, either regress spontaneously or remain stable without any intervention. This observation, formalized in consensus guidelines from the Desmoid Tumor Working Group, fundamentally changed the treatment algorithm: intervention, whether systemic therapy, radiation, surgery, or ablation, is now reserved for tumors that progress on surveillance or cause significant symptoms. The patients in the cryoablation study fit squarely into this modern paradigm, having been selected precisely because their disease demanded treatment after systemic options were exhausted or declined.

On the mechanistic side, cryoablation’s lethality depends on achieving sufficiently low temperatures throughout the target volume. Vascularized tissue dies reliably when cooled to roughly minus twenty to minus forty degrees Celsius, with ice crystal formation disrupting cell membranes, vascular stasis producing ischemia, and the slow thaw phase amplifying the injury. The double freeze-thaw protocol used here exploits this last phenomenon: the second cycle kills cells already sensitized by the first, and the freeze-thaw alternation damages the microvasculature more thoroughly than a single prolonged freeze. This is why the authors insisted on an ablation margin of at least five millimeters beyond the enhancing tumor boundary, since the lethal isotherm sits inside the visible edge of the ice ball.

The choice of 5 percent dextrose in water for hydrodissection is also deliberate rather than arbitrary. Isotonic saline conducts electrical current and would be hazardous with radiofrequency ablation, but for cryoablation the more relevant property is thermal: fluid placed between tumor and bowel acts as a physical and thermal buffer, pushing heat-rich structures out of the freeze zone. Dextrose solution also avoids the theoretical concern of saline’s higher thermal conductivity accelerating ice growth toward protected structures.

Finally, the emergence of gamma-secretase inhibitors, exemplified by nirogacestat’s regulatory approval based on randomized trial evidence, has added a systemic option that did not exist for most of the study period. How ablation and these targeted agents will be sequenced remains an open question, and head-to-head comparisons incorporating volumetric endpoints, patient-reported symptom scores, and cost-effectiveness analysis will be needed to define each therapy’s proper place in a disease whose natural history is as variable as its treatment options are expanding.

Subject of Research: Percutaneous CT-guided cryoablation of desmoid tumors with volumetric MRI outcome assessment

Article Title: Percutaneous CT-guided cryoablation of desmoid tumors: single-center experience with volumetric midterm outcome

Article References: Schaaf, M., Sattler, T., Spatz, J., Surwald, S., Schraut, J., & Jakobs, T. F. (2026). Percutaneous CT-guided cryoablation of desmoid tumors: single-center experience with volumetric midterm outcome. CVIR Oncology, 2(1), Article 22. https://doi.org/10.1007/s44343-026-00060-4

Image Credits: AI Generated

DOI: 10.1007/s44343-026-00060-4

Keywords: desmoid tumor, cryoablation, aggressive fibromatosis, interventional radiology, CT-guided ablation, volumetric assessment, mRECIST, MRI, hydrodissection, soft tissue tumor, minimally invasive, local recurrence