Uncommon initial presentation of a gastric mass in a patient with primary plasma cell leukemia: a case report

Abstract

Background

Extramedullary infiltration is a recognized manifestation of primary plasma cell leukemia (pPCL); however, presentation as a gastric mass is rarely reported. This report describes a rare case of pPCL complicated with prostate cancer, initially presenting as a gastric mass, and outlines the pathogenic mechanisms and clinical management course.

Case summary

A 68-year-old man presented with intermittent epigastric pain. Contrast-enhanced abdominal computed tomography (CT) revealed a gastric mass measuring 97 mm × 131 mm × 63 mm, subsequently confirmed as an extramedullary plasmacytoma on pathological examination. Bone marrow biopsy and peripheral blood immunophenotyping established the diagnosis of pPCL with gastric involvement. In view of an elevated prostate-specific antigen level, a targeted prostate biopsy was performed, confirming concomitant prostate cancer. The patient received three cycles of the Dara-RVD regimen for pPCL, along with leuprolide acetate and bicalutamide for prostate cancer. Follow-up evaluation demonstrated partial remission of pPCL.

Conclusion

Additional case accumulation and further investigation of pathogenic mechanisms are warranted to optimize diagnostic approaches and improve therapeutic outcomes.

Introduction

Plasma cell leukemia (PCL) is a rare plasma cell-derived malignancy, accounting for approximately 1%–2% of newly diagnosed multiple myeloma (NDMM) cases [1–3]. Based on prior multiple myeloma (MM) history, PCL is categorized into primary PCL (pPCL) and secondary PCL (sPCL) [4]. In the 2021 update of the International Myeloma Working Group (IMWG), pPCL is defined as a malignant plasma cell disorder, requiring the fulfillment of multiple myeloma (MM) diagnostic criteria plus a peripheral blood circulating plasma cell (CPC) proportion of ≥ 5% [4]. Extramedullary infiltration is more prevalent in pPCL than in MM—typically manifesting as hepatomegaly, splenomegaly, and lymphadenopathy; however, gastric involvement is rarely reported [5, 6]. We report this unusual case of pPCL with an initial gastric mass manifestation in a patient with concomitant prostate cancer, and review its clinical features, possible pathogenesis and treatment strategy.

Case report

In August 2025, a 68-year-old man presented with a 6-month history of intermittent epigastric pain, acid regurgitation and occasional abdominal distension, and was initially evaluated at another hospital. Physical examination revealed deep mid-upper abdominal tenderness without rebound tenderness. Gastroscopy demonstrated a subcardiac ulcer (Fig. 1A-D). The patient was referred to the Department of Gastrointestinal Surgery at our hospital for further management. Carcinoembryonic antigen (CEA) and carbohydrate antigen 19–9 (CA19-9) levels were within normal limits. Immunohistochemistry of the gastric lesion showed positivity for CD38, CD138, CD79α, BCL-2, and MUM-1, and negativity for CD5, CD10, CD20, CD21, CD23, BCL-6, and Cyclin D1. The Ki-67 proliferation index was 50%, supporting a diagnosis of extramedullary plasmacytoma (Fig. 1E-O). The patient was then referred to the Department of Hematology for evaluation of a hematologic malignancy. Serum free light chain assay: κ and λ FLC levels were within normal range, with a normal κ/λ ratio. Urine BJP: negative. Bone marrow (BM) assessment revealed active hyperplasia, with cytology identifying 20% abnormal plasma cells and biopsy confirming 50%–60% infiltration. The differential leucocyte count:Neutrophil 41.6%(1.21 × 10⁹/L), Lymphocyte 39.8%(1.15 × 10⁹/L), Monocyte 14.5%(0.42 × 10⁹/L), Eosinophil 3.9%(0.11 × 10⁹/L), Basophil 0.2%(0.01 × 10⁹/L);Absolute plasma cell count: 0.1595 × 10⁹/L (5.5% of total white blood cell count). Flow cytometry detected 22% abnormal plasma cells in BM and 5.5% in peripheral blood (PB); these cells expressed CD27, CD28, CD38, CD56, and CD138, with absent cytoplasmic κ (cκ) and λ (cλ) light chain expression. Fluorescence in situ hybridization (FISH) and conventional karyotyping were normal. Serum immunofixation electrophoresis was negative for M protein. These results further confirm the absence of monoclonal protein secretion and support non-secretory pPCL. Due to the patient’s financial constraints and limited in-hospital equipment, PET-CT and MRI examinations were not performed. Contrast-enhanced abdominal computed tomography (CT) demonstrated a 97 mm × 131 mm × 63 mm space-occupying lesion involving the gastric cardia and body (HU = 40) (Fig. 1P). During evaluation to exclude additional malignancies, serum prostate-specific antigen (PSA) was elevated at 17.4 ng/mL. Transrectal prostate biopsy demonstrated positive staining for PSA, P504S, and NKX3.1, and negative results for p63 and HMWCK. The Ki-67 proliferation index was 10%. Collectively, these pathological and immunohistochemical findings confirmed prostate cancer. The patient was diagnosed with non-secretory pPCL and prostate cancer (Gleason score 3 + 4, clinical stage, T1cN0M0). He received two cycles of the Dara-RVD regimen (daratumumab, lenalidomide, bortezomib, dexamethasone [DEX]) for pPCL, along with subcutaneous leuprorelin (3.75 mg every 4 weeks) plus oral bicalutamide (50 mg daily) for prostate cancer. In November 2025, follow-up gastroscopy demonstrated extensive erosion and ulceration from the posterior wall of the gastric cardia to the upper posterior wall of the gastric body (Fig. 2A-C). Contrast-enhanced whole-abdominal computed tomography (CT) demonstrated a reduced gastric mass measuring 22 mm × 62 mm × 40 mm (HU = 19) (Fig. 2D). PB immunophenotyping detected no abnormal plasma cells, whereas BM cytology identified 8% abnormal plasma cells and biopsy revealed 10%–20% infiltration. These findings indicated partial remission (PR). However, recurrent generalized pruritic rash prompted modification of therapy to Dara-PVD (daratumumab, pomalidomide, bortezomib, and DEX). In February 2026, gastroscopy revealed elevated lesions at the mid-gastric angle and greater curvature of the antrum (Figs. 2E–G). CT showed further reduction of the gastric mass to 19 mm × 55 mm × 20 mm (HU = 28) (Fig. 2H). PB immunophenotyping remained negative for abnormal plasma cells. BM cytology identified 2% abnormal plasma cells, and biopsy demonstrated < 10% infiltration. Histopathology of the gastric lesion demonstrated plasmacytoid cell infiltration with mild atypia in the mucosa of the gastric angle and greater curvature of the gastric antrum. The PSA level decreased to 0.01 ng/mL. These findings were consistent with PR. To date, the patient continues regular treatment and remains clinically stable. The treatment course is summarized in Fig. 3.

Fig. 1.

Laboratory examinations of the gastric mass at diagnosis. A-D Gastroscopy revealing ulcer formation from the cardia to the upper gastric body. E-O Pathological examinations: hematoxylin and eosin (HE) staining × 40 and × 400; BCL-2, CD5, CD10, CD38, CD79a, CD138, Cyclin D1, and MUM-1 immunohistochemical staining × 400; Ki-67 proliferation index 50%. P Contrast-enhanced abdominal computed tomography (CT) showing a lesion measuring 97 mm × 131 mm × 63 mm involving the gastric cardia and body (HU = 40)

Fig. 2.

Laboratory examinations of the gastric mass during follow-up. A-C Gastroscopy revealing ulcer formation from the cardia to the upper gastric body in November 2025. D Contrast-enhanced abdominal CT demonstrating a lesion measuring 22 mm × 62 mm × 40 mm involving the gastric cardia and body (HU = 19). E–G Gastroscopy revealing ulcer formation from the cardia to the upper gastric body in February 2026. H Contrast-enhanced abdominal CT showing a lesion measuring 19 mm × 55 mm × 20 mm involving the gastric cardia and body (HU = 28)

Fig. 3.

Treatment course and efficacy assessment

Discussion

Primary plasma cell leukemia (pPCL) is characterized by acute onset, high early mortality, and poor prognosis [7]. Compared with MM, pPCL carries a higher risk of extramedullary infiltration (EMI). A prior study of 27 patients with pPCL reported EMI in 18 cases (66.7%) [8]. Hepatomegaly, splenomegaly, and lymphadenopathy are well-recognized manifestations of EMI in pPCL. Therefore, presentation as a gastric mass, as in our patient, is extremely rare and may be misdiagnosed as gastric cancer. Gastric adenocarcinoma typically manifests as localized ulcers or masses accompanied by focal gastric wall thickening [9]. In contrast, gastric lymphoma is characterized by diffuse gastric wall thickening and multiple mucosal nodules on endoscopy and imaging [10]. Significant differences in endoscopic and imaging manifestations, as well as pathological origins, exist among these three entities, which further strengthens the differential diagnostic value and clinical implication of the present case.

The mechanisms underlying EMI in plasma cell disorders remain incompletely understood [11]. Current evidence suggests that malignant plasma cells exit the BM microenvironment, circulate in PB, and subsequently colonize extramedullary sites [12]. EMI is synergistically driven by interactions between tumor-intrinsic factors and the microenvironment, including adhesion molecules (such as CD56, CD44, VLA-4, and CD11b), genetic alterations (such as TP53, RAS, and MYC), and chemokines (such as CXCL13 and CCL19). Downregulation of CD56 facilitates plasma cell detachment from the BM and dissemination into PB [13]. Loss of CD27 expression has also been linked to activation of nuclear factor kappa B (NF-κB)-mediated antiapoptotic pathways that support plasma cell survival [14]. Additionally, elevated CD54 expression has been shown to enhance migration of malignant plasma cells to extramedullary sites and promote systemic dissemination [15]. Increasing evidence indicates that non-coding RNAs are dysregulated in MM and closely correlated with key pathological features [16, 17]. These molecules may modulate disease progression within the BM microenvironment and contribute to EMI development [18]. Notably, this case showed rare CD56 positivity, a finding inconsistent with previous reports. Preserved CD56 expression suggests a less aggressive disease biology and retains the stromal adhesion capability of malignant plasma cells, which may limit extensive extramedullary dissemination. In this clinical scenario, CD56 positivity represents an atypical phenotypic variant of plasma cell leukemia. Even with retained CD56 adhesion, gastric microenvironmental chemokines counteract its anchoring effect by recruiting malignant plasma cells for local proliferation, eventually forming bulky gastric tumor. As no gene mutation analysis or transcriptome sequencing was performed, the mechanism underlying gastric infiltration requires unclear and warrants further investigation.

There is no established standard treatment for pPCL and conventional chemotherapy has limited efficacy, with a median survival of approximately 6 months and poor long-term outcomes [19]. Novel agents, including proteasome inhibitors (PIs), immunomodulators (IMiDs), and CD38 monoclonal antibodies, have improved response and survival rates [20]. For example, Katodritou et al. [21] analyzed 50 patients with pPCL treated with bortezomib-based regimens, reporting 6% early mortality and median progression-free survival (PFS) and overall survival (OS) of 12 and 18 months, respectively. A phase II clinical trial evaluated lenalidomide and DEX induction in 23 patients with pPCL after four treatment cycles [19], demonstrating an overall response rate (ORR) of 73.9% and a median OS of 28 months. Currently, CD38 antibody–based quadruple regimens incorporating IMiDs, PIs, and DEX are the preferred treatment approach. A multicenter study of 24 patients treated with CD38-based therapy [22], reported an ORR of 83.3% and a median PFS of 20.5 months. Chimeric antigen receptor T-cell (CAR-T) and bispecific antibodies (BsAb) may further remodel the tumor microenvironment and represent promising therapeutic options for pPCL [23]. As BCL-2 inhibitors are effective in MM with t(11;14), they may represent a promising option for pPCL [24]. Hematopoietic stem cell transplantation is recommended following induction therapy [25], and autologous or tandem hematopoietic stem cell transplantation may improve survival and reduce early relapse [5]. Initial Dara-RVD was chosen for this high-risk plasma cell leukemia due to its favorable treatment response and suitability for the patient’s baseline condition. The subsequent conversion to Dara-PVD was determined by treatment tolerance and the need for sustained disease control, rather than adverse effects alone. Although stem cell transplantation was considered, it was omitted because of advanced age and unavailability of donors. PR was defined by: ≥ 50% reduction in bone marrow plasma cells, Marked shrinkage of extramedullary gastric mass, No circulating abnormal plasma cells. Our patient achieved PR following two cycles of Dara-RVD; however, further management remained challenging due to advanced age and absence of a suitable sibling donor. The co-existence of plasma cell leukemia and prostate cancer further increased therapeutic complexity. The two cited prior studies [26, 27] are case reports that described clinical features and therapeutic regimens of patients with combined dual tumors. Their research findings provide meaningful reference for the clinical evaluation and treatment decision-making of the current case. Meanwhile, we have consulted urology specialists. After collective discussion, we concluded that the two tumors require independent therapeutic management and their treatments are mutually irrelevant.

This case report outlines the diagnostic process and treatment course of a patient with pPCL complicated by prostate cancer, initially presented with a gastric mass. It provides additional insights into the differential diagnosis of gastric neoplasms and management of dual primary malignancies. However, certain limitations should be acknowledged. First, as a single-case report, it cannot fully represent the clinical spectrum of this rare condition. Second, the absence of comprehensive sequencing limits interpretation of the molecular mechanisms underlying dual malignancy and gastric infiltration. Finally, the relatively short follow-up period precludes robust and long-term assessment of outcomes and prognosis.

Authors’ contributions

Shao-juan Cui and Hang Yin wrote the manuscript and provided images. Chun-li Xu contributed to the manuscript preparation. Dong-ping Huang,Yu Chen and Zhao-ying Wu supervised the study. All authors analyzed the data, reviewed, and approved the final manuscript.

Funding

This work was supported by the Health Research Project of Anhui Province (AHWJ2023A30148); Bethune Charity Foundation (BFC-QYWL-QL-20240905–09); and the 2025 Key Natural Science Research Projects of Anhui Provincial Higher Education Institutions (2025AHGXZK31067).The 2023 "Hengrui · Tianqing Medical Education Fund" horizontal project of the Second Affiliated Hospital of Wannan Medical College (HXKT2022024).

Data availability

The data supporting this study's findings are available from the corresponding author upon reasonable request.

Declarations

Ethics approval and consent to participate

This study protocol was reviewed and approved by the ethics committee of the Second Affiliated Hospital of Wannan Medical College (approval number WYEFYLS2023019). Written informed consent was obtained from the patient for publication of clinical details and accompanying images. The patient’s data were anonymized and de-identified prior to analysis. All case information presented in this study was collected with written informed consent obtained from the patients.

Consent for publication

Each author has approved the final version of the manuscript for publication.The case information involved in this article has been approved for publication.

Competing interests

The authors declare no competing interests.