Primary Breast Myeloid Sarcoma Mimicking Breast Carcinoma: A Case Report

Abstract

Background

Myeloid sarcoma (MS) is a rare extramedullary tumor composed of immature myeloid cells, most commonly associated with acute myeloid leukemia (AML). Although it typically occurs in the skin, lymph nodes, bone, and soft tissue, breast involvement is extremely uncommon and may mimic breast carcinoma or lymphoma.

Case Report

A 34-year-old woman presented with a left breast mass initially suspected to be carcinoma. Histopathological and immunohistochemical analyses confirmed myeloid sarcoma, with no evidence of systemic involvement. The patient achieved complete remission after AML-based induction chemotherapy followed by allogeneic stem cell transplantation and remains in remission at one year of follow-up.

Conclusion

Breast MS is a rare and diagnostically challenging entity. Accurate immunohistochemical evaluation is crucial to avoid misdiagnosis and treatment delay. AML-oriented systemic chemotherapy, and allogeneic stem cell transplantation when appropriate, remain the most effective strategies to achieve long-term remission.

Introduction

Myeloid sarcoma (MS) is defined as a tumor mass composed of myeloblasts or immature myeloid cells occurring in an extramedullary site or bone.¹ It is also referred to as granulocytic sarcoma, extramedullary leukemia, or chloroma. MS may arise de novo or in association with acute myeloid leukemia (AML) or a myeloproliferative disorder.¹ According to the U.S. National Cancer Database, between 2004 and 2013, a total of 94,185 AML cases were reported, of which 746 (0.8%) were diagnosed as extramedullary MS. In that study, the most common sites of involvement were connective and soft tissue (31%), skin and breast (12%), gastrointestinal tract (10%), lymph nodes (10%), bone and joints (6%), and the nervous system (6%).² Tumors involving the genitourinary and gastrointestinal systems have been noted to carry a better prognosis than those affecting the nervous system, soft tissue, and lymph nodes.³

Isolated breast MS is extremely rare and can be easily misdiagnosed as breast carcinoma or lymphoma. Because of its rarity, current clinical knowledge is largely based on small case series. Here, we report a case of primary breast MS without bone marrow involvement, treated successfully with chemotherapy followed by allogeneic transplantation.

CASE REPORT

A 34-year-old woman presented to the general surgery clinic with a palpable mass in the left breast. Positron emission tomography–computed tomography (PET-CT) revealed a 56 × 48 × 79 mm hypermetabolic lesion in the upper quadrant of the left breast (SUV_max: 19.80) and axillary lymph nodes with metabolic uptake measuring up to 13 mm in diameter (SUV_max: 5.35) (Fig. 1). With an initial suspicion of breast carcinoma, a tru-cut biopsy was performed. Histopathological analysis revealed areas of benign-appearing mammary ducts and acini alongside diffuse infiltration of hyperchromatic, narrow-cytoplasmic atypical cells. Immunohistochemical studies showed diffuse positivity for CD34, CD117, CD43, and CD45; focal positivity for TdT, CD33, and myeloperoxidase (MPO); and negativity for pancytokeratin. The Ki-67 proliferation index was approximately 70% (Figs. 2, 3). The immunophenotypic profile was consistent with myeloid sarcoma. Following this, the patient underwent a modified radical mastectomy, which yielded a 6.5 × 6.5 × 5.6 cm mass. She presented to the hematology department after surgery. Peripheral blood smear and complete blood count were normal. Bone marrow examination and cytogenetic studies showed no abnormalities, confirming the diagnosis of primary breast MS. The patient was treated with induction chemotherapy consisting of idarubicin (12 mg/m² for three days) and cytarabine (100 mg/m² for seven days). Post-treatment PET-CT revealed a complete metabolic response. Subsequently, the patient underwent allogeneic hematopoietic stem cell transplantation from a human leukocyte antigen (HLA)-matched sibling and remains in remission at one year post-transplant.

Figure 1.

Positron emission tomography–computed tomography (PET-CT) image showing a hypermetabolic mass lesion measuring 56 × 48 × 79 mm located in the upper quadrant of the left breast near the midline (SUV_max: 19.80).

Figure 2.

Hematoxylin and eosin-stained (H&E) sections of breast biopsy specimens. Focal areas of mammary stroma and epithelial cells (arrows) are observed, while the remaining areas are composed of tumor tissue. The tumor cells show diffuse infiltration with large hyperchromatic nuclei and scant cytoplasm (a and b, ×40; c, ×100; d, ×200).

Figure 3.

Immunohistochemical findings of tumor cells. Diffuse positivity for CD34 (a) and CD117 (b); focal positivity for TdT (c). Most tumor cells show immunopositivity for CD43 (d) and CD45 (e). Focal positivity is observed for CD33 (f) and myeloperoxidase (MPO) (g). Tumor cells are negative for pancytokeratin, while benign mammary ducts show positivity (arrow) (H). A high proliferation index is demonstrated with Ki-67 staining (I). (a–h, ×100; i, ×40).

DISCUSSION

Myeloid sarcoma is a rare malignant proliferation of immature myeloid cells at extramedullary sites, most often associated with AML. Isolated involvement of the breast is exceptionally uncommon and is frequently misdiagnosed as breast carcinoma or lymphoma.^4,5 Large series suggest that breast involvement accounts for only 0.1–0.2% of all extramedullary MS cases.² Therefore, primary breast MS represents a major diagnostic and therapeutic challenge.

Immunohistochemistry is indispensable in the diagnostic process. MS typically expresses markers such as CD34, CD117, MPO, CD43, and CD45, while lacking epithelial or lymphoid markers such as cytokeratin, CD20, or CD3.^3,5 Misdiagnosis often occurs due to limited immunohistochemical studies or inadequate biopsy samples. In our case, as in previous reports, an initial misdiagnosis of breast carcinoma was corrected after a comprehensive immunohistochemical panel confirmed MS.

There is no consensus on the optimal treatment; however, the literature strongly supports AML-type systemic chemotherapy as the most appropriate approach. In a large national dataset, Goyal et al.² demonstrated that 37.7% of MS patients receiving early chemotherapy showed improved survival outcomes. Similarly, Tsimberidou et al.⁶ reported a complete remission rate of 65% in nonleukemic MS patients treated with AML-type chemotherapy. Long-term survival is most consistently observed in patients undergoing allogeneic stem cell transplantation.³ Our case also achieved complete remission with induction chemotherapy, followed by sustained remission after allogeneic transplantation.

Radiotherapy is considered a radiosensitive and useful local treatment option in selected cases of myeloid sarcoma, particularly for residual or recurrent lesions. However, current literature emphasizes that myeloid sarcoma of the breast should be managed primarily with AML-type systemic chemotherapy, while surgery and/or radiotherapy are mainly used for local control rather than as sole treatment modalities.⁷ In our patient, wide surgical excision had already been performed, no residual tumor was detected after mastectomy, and systemic chemotherapy was planned; therefore, radiotherapy was not administered.

From a prognostic perspective, Pileri et al.,³ in their series of 92 adult MS patients, reported cytogenetic abnormalities in approximately 54% of cases, with monosomy 7 and trisomy 8 associated with worse outcomes. Given the rarity of isolated breast MS, prognostic data remain limited; however, progression to AML has been documented in a significant proportion of cases during follow-up.^5,8 This underscores the importance of close hematologic monitoring and regular bone marrow evaluation.

CONCLUSION

Taken together, these findings suggest that a broad immunohistochemical panel is essential for accurate diagnosis of primary breast MS. AML-type systemic chemotherapy remains the cornerstone of treatment, while allogeneic stem cell transplantation should be considered for long-term disease control. Regular hematologic follow-up is critical to detect early progression to AML.

Ethics Committee Approval

This is a single case report, and therefore ethics committee approval was not required in accordance with institutional policies.

Informed Consent

Written informed consent was obtained from the patient who participated in this study.

Conflict of Interest

The authors have no conflicts of interest to declare.

Funding

The authors declared that this study received no financial support.

Use of AI for Writing Assistance

No use of AI-assisted technologies was declared by the authors.

Author Contributions

Concept – SD, TFK; Design – SD, TFK; Supervision – AT, MM; Resource – FK, HHE; Materials – FK, HHE, ME; Data Collection and/or Processing – SD, TFK, FK, HHE, ME; Analysis and/ or Interpretation – SD, FK, HHE, ME; Literature Review – SD, TFK; Writing – SD, TFK; Critical Review – AT, MM.

Peer-review

Externally peer-reviewed.