Pleomorphic gastric leiomyosarcoma with retroperitoneal extension and hepatic metastasis: A case report

Abstract

BACKGROUND

Pleomorphic leiomyosarcoma (LMS) of gastric origin is extremely rare, especially when accompanied by retroperitoneal extension and hepatic metastasis. Since the introduction of KIT (cluster of differentiation 117) immunohistochemistry, many gastric mesenchymal tumors have been reclassified as gastrointestinal stromal tumors, making true gastric LMS unusual. We report a large pleomorphic gastric LMS initially misdiagnosed as retroperitoneal sarcoma to highlight diagnostic pitfalls and the central role of complete surgical resection.

CASE SUMMARY

A 58-year-old woman presented with a 1-month history of progressive abdominal distension and bilateral lower limb edema and had a 1-year history of a self-palpated abdominal mass. Computed tomography showed a 26.8 cm heterogeneous abdominal mass, a 4.4 cm left hepatic lesion, and a left adrenal nodule, suggesting retroperitoneal sarcoma with hepatic metastasis. Laparotomy revealed a tumor arising from the gastric greater curvature invading the pancreatic body-tail and a synchronous liver metastasis. Margin-negative (R0) resection, including partial gastrectomy, distal pancreatectomy, and partial hepatectomy, was performed. Histology and immunohistochemistry confirmed pleomorphic LMS. The patient declined chemotherapy and took Huaier granules as adjunctive therapy. No recurrence was detected during 17 months of follow-up.

CONCLUSION

Pleomorphic gastric LMS may mimic retroperitoneal sarcoma, and complete margin-negative (R0) resection remains the key treatment.

Key Words: Pleomorphic leiomyosarcoma; Stomach neoplasms; Retroperitoneal involvement; Liver metastasis; Surgical resection; Traditional Chinese medicine; Huaier granules; Case report

Core Tip: Pleomorphic leiomyosarcoma of gastric origin is an exceptionally rare and aggressive tumor, especially when accompanied by retroperitoneal invasion and hepatic metastasis. We report a unique case initially misdiagnosed as retroperitoneal sarcoma, later confirmed intraoperatively to arise from the stomach near the pylorus. Complete curative (R0) resection including distal pancreatectomy and partial hepatectomy achieved favorable short-term outcomes. The patient refused conventional adjuvant therapy and received Huaier granules, a traditional Chinese medicine with potential antitumor effects. This case emphasizes the diagnostic challenges of gastric leiomyosarcoma and suggests that Huaier granules may have a role in postoperative disease control.

INTRODUCTION

Soft tissue sarcomas are rare neoplasms, accounting for less than 1% of newly diagnosed adult cancers, and approximately 10%-15% of these tumors arise in the retroperitoneum[1,2]. Leiomyosarcoma (LMS) accounts for 10%-20% of retroperitoneal soft tissue sarcomas and is characterized by aggressive local invasion and a high rate of distant metastasis, most commonly to the liver[3]. The pleomorphic variant, marked by significant cellular atypia and high mitotic activity, constitutes about 8.6% of LMS cases[4]. In the post-KIT era, after the routine introduction of cluster of differentiation 117 (CD117) (KIT) and discovered on gastrointestinal stromal tumor 1 (DOG1) immunohistochemistry, most gastric mesenchymal tumors previously regarded as smooth muscle neoplasms have been reclassified as gastrointestinal stromal tumors, and true gastric LMS has become an exceedingly rare entity[5,6]. Pleomorphic LMS arising from the stomach, particularly in the distal stomach near the pylorus, has only been described in sporadic case reports[7-10].

Here, we report a case of pleomorphic gastric LMS with retroperitoneal extension and synchronous hepatic metastasis. The patient underwent complete (R0) surgical resection and subsequently chose Huaier granules, a traditional Chinese medicine with reported antitumor properties, as exploratory adjunctive therapy. We briefly review the relevant literature and discuss the diagnostic challenges and therapeutic considerations for this rare entity.

CASE PRESENTATION

Chief complaints

A 58-year-old woman presented on March 29, 2024, with a 1-month history of progressive abdominal distension and bilateral lower limb edema, on a background of an incidentally palpated abdominal mass noted approximately 1 year earlier.

History of present illness

One year before admission, the patient accidentally noticed a palpable abdominal mass that was initially asymptomatic and did not affect her daily life. During the month before presentation, she developed gradually worsening abdominal distension accompanied by bilateral lower limb edema. She sought care at a local hospital, where symptomatic treatment failed to relieve her symptoms. Abdominal ultrasound performed on March 28, 2024, revealed a hepatic space-occupying lesion, and she was referred to our institution on March 29, 2024, with a provisional diagnosis of “hepatic space-occupying lesion” for further evaluation and management.

History of past illness

Her past medical history was notable for hypertension since 2018, which was well controlled with oral amlodipine and bisoprolol. She also had a history of cerebellar hemorrhage in 2018, with no residual neurological deficits. No other significant chronic illnesses, previous abdominal surgeries, or known drug allergies were recorded.

Personal and family history

There was no documented history of tobacco or excessive alcohol use. No family history of malignant tumors or hereditary disorders relevant to the present disease was reported.

Physical examination

On admission, the patient was in a generally good condition with obvious abdominal distension and bilateral lower limb edema. A large, ill-defined abdominal mass was palpable in the upper abdomen. No additional remarkable findings were documented on systemic examination.

Laboratory examinations

Baseline laboratory examinations, including routine blood tests, serum biochemistry, coagulation profile, and tumor markers, were obtained as part of the preoperative assessment. The results did not provide specific clues beyond confirming that the patient was fit for major abdominal surgery.

Imaging examinations

Preoperative contrast-enhanced computed tomography on March 29, 2024 demonstrated a 14.1 cm × 18.6 cm × 26.8 cm heterogeneous mass occupying the hepatogastric space, with patchy low-density areas and extension toward the pelvis. A 4.4 cm × 3.9 cm lesion consistent with hepatic metastasis was identified in the left liver lobe, showing uneven enhancement and tortuous vascular shadows (Figure 1). The mass displaced the stomach anteriorly and to the left and pushed the pancreas posteriorly, with loss of the intervening fat plane and indistinct borders between the mass and the left hepatic lobe. Based on these imaging findings, the initial radiological impression favored a retroperitoneal-origin tumor, which was later corrected intraoperatively.

Figure 1 Preoperative contrast-enhanced computed tomography images. A: Hepatic metastatic lesion (4.4 cm × 3.9 cm); B: Mid-level tumor imaging (orange arrow, 14.1 cm × 18.6 cm × 26.8 cm); C: Tumor extension to the pelvic level. Orange arrow: The tumor mass.

MULTIDISCIPLINARY EXPERT CONSULTATION

No formal multidisciplinary expert consultation was convened. The treatment strategy was developed through discussions within the hepatopancreatobiliary surgery team and anesthesiology, taking into account the patient’s symptoms, imaging findings suggestive of a large abdominal mass with hepatic metastasis, and overall functional status. The consensus was that complete surgical resection offered the best chance for disease control and symptom relief.

FINAL DIAGNOSIS

Postoperative histopathology of the resected specimen revealed spindle-shaped tumor cells with marked nuclear pleomorphism, multinucleated giant cells, and more than 10 mitotic figures per 10 high-power fields, with a Ki-67 proliferation index of 60%. These findings were consistent with pleomorphic LMS, graded as French Federation of Cancer Centers Sarcoma Group grade III. Immunohistochemistry showed diffuse positivity for smooth muscle actin and desmin, and negativity for CD117 (KIT) and DOG1, ruling out gastrointestinal stromal tumor (Figure 2). The gastric origin of the tumor arising from the greater curvature near the pylorus, with retroperitoneal extension and synchronous hepatic metastasis, was confirmed intraoperatively and histologically. The final diagnosis was pleomorphic LMS of gastric origin (French Federation of Cancer Centers Sarcoma Group grade III) with retroperitoneal involvement and synchronous liver metastasis.

Figure 2 Intraoperative and resected specimen views. A: Preoperative abdominal distension; B: Gross view post-resection; C: Cross-sectional view of abdominal tumor; D: Cross-sectional view of hepatic metastasis.

TREATMENT

On April 9, 2024, the patient underwent open exploratory laparotomy. Intraoperative exploration confirmed a 14.1 cm × 18.6 cm × 26.8 cm mass originating from the gastric greater curvature near the pylorus, extending posteriorly into the retroperitoneal space and invading the pancreatic body and tail, which appeared atrophic. A 4.4 cm × 3.9 cm metastatic lesion was identified in the left liver lobe, and there was no evidence of peritoneal seeding or distant extra-abdominal metastases.

Complete margin-negative (R0) resection was achieved through en bloc removal of the primary tumor and involved structures, including partial gastrectomy, distal pancreatectomy, and partial hepatectomy. The resected specimen weighed approximately 8 kg, and intraoperative frozen-section analysis confirmed negative surgical margins. Representative intraoperative and specimen photographs are shown in Figure 3. No major intraoperative complications were encountered, and hemostasis and reconstruction were satisfactory.

Figure 3 Histopathological and immunohistochemical findings. A-C: Hematoxylin and eosin staining at 100 ×, 200 ×, and 400 ×; D-F: Immunohistochemistry for smooth muscle actin (100 ×), desmin (100 ×), and caldesmon (100 ×).

OUTCOME AND FOLLOW-UP

The patient recovered well postoperatively and was discharged in stable condition. Her abdominal distension and bilateral lower limb edema resolved completely, and her performance status improved.

She was followed regularly in the outpatient clinic with clinical examinations, laboratory tests, and imaging studies. Follow-up abdominal contrast-enhanced computed tomography and chest imaging were performed at regular intervals to monitor for local recurrence or distant metastasis. At 17 months after surgery (September 14, 2025), no radiological or clinical evidence of tumor recurrence or new metastasis was detected, indicating favorable short-term disease control. The patient continues under active surveillance, and long-term outcomes remain to be determined.

DISCUSSION

Primary gastric LMS is an exceedingly rare malignancy, particularly in the era following the introduction of CD117 (KIT) and DOG1 immunohistochemistry, when many historical gastric “smooth muscle” tumors were reclassified as gastrointestinal stromal tumors. True gastric LMS accounts for less than 1% of gastric mesenchymal neoplasms, with the pleomorphic subtype representing an even rarer histologic variant. Over the past two decades, only a handful of pleomorphic gastric LMS cases have been reported, most arising near the pylorus and presenting as large, locally invasive tumors occasionally accompanied by hepatic metastasis[5,7,10-12]. The pleomorphic subtype of LMS is characterized by marked nuclear atypia, multinucleated tumor giant cells, and high mitotic activity. In a large clinicopathologic series, pleomorphic LMS accounted for approximately 8%-9% of all LMS cases[4]. This subtype demonstrates particularly aggressive biological behavior, with high recurrence and metastatic rates (reported in 40%-60% of cases)[13]. The most common metastatic sites are the lungs and liver, although peritoneal and osseous dissemination have also been reported[14-17]. Our case showed synchronous hepatic metastasis and retroperitoneal extension, illustrating the aggressive nature and diagnostic challenge of this tumor.

Preoperative differentiation between gastric-origin LMS and retroperitoneal sarcoma can be difficult, as both may appear as large heterogeneous masses with poorly defined boundaries on imaging. In our patient, the loss of fat planes between the mass, pancreas, and liver led to the initial misdiagnosis of retroperitoneal sarcoma. Intraoperative findings confirming a gastric origin near the pylorus highlight the importance of comprehensive exploration and intraoperative pathological assessment.

Complete surgical resection with negative margins (R0) remains the mainstay and only potentially curative treatment for LMS, regardless of its site[18,19]. In gastric LMS, prognosis depends primarily on tumor size, grade, and resection status. Adjuvant chemotherapy or radiotherapy has limited efficacy, and no standard regimen has been established. Anthracycline- or gemcitabine-based protocols may provide modest benefit in selected metastatic cases, but evidence remains inconclusive.

Our patient declined systemic chemotherapy and instead received Huaier granules (Trametes robiniophila), a traditional Chinese medicine with reported antiangiogenic and immunomodulatory effects. Although no clinical data exist on its efficacy in LMS, studies in hepatocellular carcinoma and breast cancer have suggested that Huaier extracts can inhibit proliferation and metastasis through tumor microenvironment modulation. The patient remained recurrence-free at 17 months after complete resection; however, causality cannot be inferred, and longer follow-up is warranted.

Overall, the prognosis of gastric LMS remains poor, though some series (for example, Mayo Clinic data) report 5-year survival rates around 45%, especially in patients with low-grade tumors, early stage, and without metastasis at presentation[20,21]. Pleomorphic variants, due to their high proliferative activity and resistance to systemic therapy, are associated with particularly unfavorable outcomes. Nonetheless, complete resection remains the most important prognostic factor, and close postoperative surveillance is mandatory.

Taken together, pleomorphic gastric LMS is an exceptionally rare and aggressive soft-tissue sarcoma that may mimic retroperitoneal sarcoma on imaging. Accurate diagnosis requires integration of radiological, intraoperative, and immunohistochemical findings to exclude gastrointestinal stromal tumor. Complete surgical excision remains the cornerstone of management. This case underscores the diagnostic challenges of pleomorphic gastric LMS and the importance of complete resection as the cornerstone of management. Longer follow-up and further clinical studies are needed to clarify any potential role of Huaier as an adjunct.

CONCLUSION

Pleomorphic LMS of gastric origin with retroperitoneal extension and synchronous hepatic metastasis is exceptionally rare and can mimic retroperitoneal sarcoma on preoperative imaging. Accurate diagnosis requires integration of radiologic findings, comprehensive intraoperative assessment, and immunohistochemistry to distinguish it from gastrointestinal stromal tumor and other sarcomas. Complete margin-negative resection of the primary tumor and metastatic lesions remains the key determinant of short-term disease control and survival. Complementary therapies such as Huaier granules should be considered exploratory and cannot replace standard oncologic treatments, but they may be discussed with patients in the context of shared decision-making and careful follow-up.