Myeloid sarcoma of the sternum with regional lymph node involvement in a 6-year-old child: a case report

Abstract

Background

Myeloid sarcoma is a rare extramedullary tumor composed of myeloid progenitor cells, often associated with acute myeloid leukemia or other hematologic malignancies. Primary involvement of the sternum in children is extremely uncommon and may pose substantial diagnostic challenges.

Case presentation

A 6-year-old boy presented with recurrent sternal pain lasting over four months, along with low back pain, bilateral breast pain, and fever. Imaging showed a destructive sternal lesion with an adjacent soft tissue mass, initially raising suspicion for Ewing sarcoma. Bone marrow aspiration demonstrated active hematopoiesis without increased blasts or leukemic infiltration, and leukemia immunophenotyping showed no abnormal leukemic cell population. PET-CT demonstrated a hypermetabolic destructive sternal lesion and a hypermetabolic nodular lesion adjacent to the right internal mammary vessels, without other definite malignant lesions elsewhere in the body. Because the preoperative biopsy yielded limited cellularity and remained inconclusive, surgical resection was performed for definitive diagnosis. Histopathology and immunohistochemistry confirmed myeloid sarcoma. Two resected parasternal lymph nodes also showed tumor involvement. After surgery, the patient was transferred to the hematology department and received induction chemotherapy with the VAH regimen according to the CCLG-AML-2024 protocol. According to the final hematology assessment, the patient was classified as intermediate risk. At the latest documented follow-up in January 2026, complete blood counts remained within normal limits, and chest CT showed no obvious solid mass around the sternum or enlarged mediastinal lymph nodes.

Conclusions

Myeloid sarcoma should be considered in the differential diagnosis of pediatric chest masses, even in the absence of overt bone marrow involvement. Accurate diagnosis requires integration of imaging, histopathology, and immunohistochemistry. Surgery plays an important role in diagnostic confirmation and local control, whereas systemic AML-type chemotherapy remains the standard treatment strategy. Early recognition and multidisciplinary management are essential for improving outcomes.

Introduction

Myeloid sarcoma (MS), also known as granulocytic sarcoma or green tumor, is a neoplasm characterized by the localized infiltration of myeloid progenitor cells, which can lead to the destruction of underlying tissue architecture [1]. MS may occur concurrently with acute myeloid leukemia (AML), precede the onset of AML, or represent relapse in patients with a history of myeloid neoplasms. In some patients, MS presents without overt bone marrow leukemia, which is often described as isolated or non-leukemic MS [2]. In children, the skin and orbit are among the most commonly involved sites, whereas primary involvement of the sternum is exceptionally rare [2, 3]. Because of its rarity and nonspecific clinical and radiologic features, MS can be easily misdiagnosed as other small round cell malignancies, especially Ewing sarcoma. Here, we report a rare case of sternal MS with regional lymph node involvement in a 6-year-old child and highlight the diagnostic challenges, pathological features, and multidisciplinary management of this disease.

Case report

A 6-year-old boy with no significant medical history presented with recurrent sternal pain persisting for over four months. A raised mass was observed over the sternum, without erythema, edema, or ulceration, but with diffuse tenderness upon palpation. Associated symptoms included bilateral breast pain, low back pain, and fever. The initial clinical impression was a bone tumor.

Baseline laboratory investigations revealed an elevated C-reactive protein level (39.54 mg/L). The white blood cell count was within the normal range (6.88 × 10⁹/L), with a mildly increased neutrophil proportion (72.7%) and decreased lymphocyte percentage (22.5%). Hemoglobin (129 g/L) and platelet count (238 × 10⁹/L) were within normal limits, and no abnormal circulating blasts were identified.

Bone marrow aspiration showed active hematopoiesis with a granulocyte-to-erythroid ratio of approximately 1.09:1 and clustered platelets, but no increase in blasts or evidence of leukemic infiltration. Leukemia immunophenotyping showed no abnormal leukemic cell population.

CT scan showed distension in the middle portion of the sternum, characterized by irregular margins and patchy areas of bone destruction. There was a slight periosteal reaction and a soft tissue mass in the surrounding area, with a CT attenuation value of approximately 54 HU. The mass measured approximately 67 mm (left to right diameter) × 38 mm (anterior to posterior diameter) × 59 mm (superior to inferior diameter) (Fig. 1A-D). Additionally, a small amount of fluid was visible in the right pleural cavity. These findings initially raised the possibility of Ewing sarcoma or other mesenchymal tissue tumors.

Fig. 1.

CT scan images of 6 year old boy case

A PET-CT scan performed at an external institution on August 28, 2024 demonstrated a destructive sternal lesion with an associated soft tissue mass measuring approximately 5.2 × 3.7 cm, with a craniocaudal extent of 5.6 cm. The lesion showed heterogeneous increased FDG uptake. A nodular soft tissue density adjacent to the right internal mammary vessels also showed increased FDG uptake, suggesting possible regional lymph node involvement. No other definite malignant lesions were identified elsewhere in the body. Mild homogeneous FDG uptake in the anterior mediastinum was considered compatible with physiological thymic activity, and symmetric uptake in the nasopharynx and oropharynx was considered consistent with mild inflammatory changes.

A preoperative needle biopsy of the thoracic lesion was performed. Histologically, the biopsy suggested a small round cell malignancy with high suspicion for Ewing sarcoma. However, immunohistochemical findings, including negative NKX2.2 staining, did not fully support this diagnosis. Because of the limited cellularity of the biopsy specimen, definitive diagnosis and further molecular confirmation could not be achieved. In view of the persistent diagnostic uncertainty and the need to guide subsequent treatment, surgical resection was undertaken.

In September 2024, the patient underwent surgical resection of the sternal tumor through a median sternal incision. Intraoperatively, a large irregular tumor encasing the sternum with poorly defined borders was identified (Fig. 2A). A portion of the tumor was sent for rapid pathological examination, which indicated a small round-cell malignant tumor, pending further clarification through extensive sampling of routine specimens.

Fig. 2.

Perioperative images of surgery and resection of tumor (A-C), Immunohistochemistry analysis of tumor specimen (D)

The tumor was dissected and freed from the surrounding tissues. The sternum was transected at the sternal handle and 2 cm above the raphe, and the 2nd-6th ribs were severed along the tumor’s edge. The dorsal sternal adherent tissues were carefully freed, and the tumor, along with parasternal lymph nodes, was excised and sent for pathological analysis. The wound was irrigated with sterilized injectable water, and three steel plates were placed to support the sternum and ribs (Figs. 1E and 2C). The chest was then fixed with steel wires, and after achieving hemostasis, the chest was closed layer by layer, with bilateral chest drains left in place. The surgery proceeded smoothly, and the child was transferred to the ICU with oral intubation postoperatively.

The tumor measured 9 × 9 × 4 cm, exhibiting a predominantly dark red hue with localized areas of greenish discoloration (Fig. 2B). The majority of the tissue section presented a greenish tint, solid yet pliable in texture. Within the mass, discernible cartilaginous and osseous tissues were evident. The larger gross specimen size, compared with the preoperative radiologic measurements, may be explained by differences in measurement methods and by inclusion of infiltrative tumor tissue that was not fully delineated on imaging.

Microscopically, hematoxylin and eosin staining revealed diffuse infiltrative growth characterized by small, round cells with uniform morphology (Fig. 2D). These cells were arranged in a “soldier-like” pattern within the fibrous tissue and striated muscle. Immunohistochemistry was positive for myeloperoxidase (MPO), CD31, CD99, CD43, CD117; it was negative for CK, Desmin, Myogenin, MyoD1, Smooth Muscle Actin (SMA), S-100, NKX2.2, CD3, CD20, CD56, CD34, CD68, Lymphocyte Common Antigen (LCA), Epithelial Membrane Antigen (EMA), Neuro Specific Enolase (NSE), Synaptophysin (SYN), and Terminal Deoxynucleotidyl Transferase (TDT). The Ki-67 proliferation index was approximately 30% in densely cellular areas. CD31 positivity was interpreted cautiously and was not considered a lineage-defining finding. Based on the overall morphologic and immunophenotypic features, a diagnosis of myeloid sarcoma was established.

Two parasternal lymph nodes resected during surgery also showed tumor involvement on pathological examination, indicating regional lymph node involvement.

On September 23, 2024, lumbar puncture and intrathecal prophylactic therapy were performed to prevent central nervous system involvement. Cerebrospinal fluid cytology and flow cytometry showed no immature cells, and routine cerebrospinal fluid and biochemical analyses showed no significant abnormalities.

After surgery, the patient was transferred to the hematology department. Beginning on September 18, 2024, induction chemotherapy was administered using the VAH regimen according to the CCLG-AML-2024 protocol. According to the final hematology assessment at our institution, the patient was diagnosed with isolated (non-leukemic) myeloid sarcoma and was classified as intermediate risk, based on the absence of bone marrow, peripheral blood, and central nervous system involvement. High-throughput sequencing of the lesion tissue was also performed.

At the latest documented follow-up, the patient was readmitted from January 6 to January 16, 2026 for protocol-based treatment and evaluation. Complete blood counts on both admission and discharge were within normal limits. Follow-up chest CT performed on January 6, 2026 showed postoperative changes of the sternum with metallic fixation in place, but no obvious solid mass around the sternum, no obvious enlarged mediastinal lymph nodes, and no pleural effusion. These findings did not show obvious radiographic evidence of local progression at the latest documented follow-up.

Discussion

Myeloid sarcoma involving the sternum in a child is extremely rare and may closely mimic other pediatric small round cell malignancies, particularly Ewing sarcoma. In our patient, the clinical presentation, destructive sternal lesion on imaging, and the initial biopsy findings all favored that differential diagnosis. Definitive diagnosis was established only after resection, based on the combined morphologic and immunophenotypic profile, especially positivity for MPO, CD43, and CD117. Although CD31 was positive, this finding was interpreted cautiously and was not considered a lineage-defining marker [4].

An important issue in this case is disease classification and staging. According to the final hematology assessment, the patient was considered to have isolated (non-leukemic) myeloid sarcoma because no peripheral blood, bone marrow, or central nervous system involvement was identified. At the same time, two parasternal lymph nodes were pathologically involved by tumor, indicating regional lymph node involvement. PET-CT demonstrated a hypermetabolic sternal lesion and a nodular lesion adjacent to the right internal mammary vessels, but no other definite malignant lesions elsewhere in the body. These findings highlight the importance of comprehensive hematologic and imaging evaluation in suspected myeloid sarcoma.

Current evidence supports AML-type systemic chemotherapy as the standard treatment strategy for myeloid sarcoma, whereas surgery mainly serves for diagnostic confirmation and local control rather than definitive treatment alone. In the present case, surgical resection provided sufficient tissue for diagnosis and achieved local control of the destructive sternal lesion, after which the patient received induction chemotherapy with the VAH regimen according to the CCLG-AML-2024 protocol and was classified as intermediate risk by the hematology team. Follow-up data were available up to January 2026, when complete blood counts remained within normal limits and chest CT showed no obvious solid mass around the sternum or enlarged mediastinal lymph nodes. Nevertheless, longer-term follow-up is still required. This case highlights that myeloid sarcoma should be considered in the differential diagnosis of pediatric chest wall masses and that early recognition together with multidisciplinary management is essential for optimal care.

Conclusions

Myeloid sarcoma should be considered in the differential diagnosis of pediatric chest wall masses, even in the absence of overt bone marrow involvement. Early diagnosis based on integrated hematologic, imaging, and pathological evaluation, followed by multidisciplinary treatment, is essential for optimal management.

Author contributions

SZB managed the patient and drafted the manuscript. LY managed the patient and obtained informed parental consent. MXM, ZYX, LH, NP, WKH were members of the surgical team and critically revised the manuscript for important intellectual content. All authors read and approved the final version of the manuscript.

Funding

The National Natural Science Foundation of China (82270310); Jiangsu Provincial key research and development program(BE2023662); Noncommunicable Chronic Diseases-National Science and Technology Major Project (No. 2024ZD0527000 and No. 2024ZD0527005).

Data availability

The datasets generated and/or analyzed during the current study are not publicly available due to patient confidentiality.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

For this case report, informed written parental consent was obtained before surgery, and it was carried out in accordance with Helsinki declarations, relevant guidelines and regulations.

Competing interests

The authors declare no competing interests.