Introduction
Multiple myeloma (MM) is a plasma cell neoplasm characterized by clonal marrow proliferation and classically associated with osteolytic lesions, anemia, renal dysfunction, and hypercalcemia [ 1 ]. A subset of patients develop extramedullary disease (EMD), representing hematogenous spread of plasma cells to soft tissues and conferring an aggressive biological phenotype with poor prognosis [ 2 , 3 ]. EMD occurs in 0.5%-4.8% of newly diagnosed and up to 14% of relapsed cases [ 4 ]. Common sites include skin, soft tissues, liver, kidneys, lymph nodes, pleura, and the central nervous system. Breast involvement is extremely rare and predominantly reported in women. Bilateral breast plasmacytomas in male patients are exceptionally uncommon [ [5] , [6] , [7] ]. We present a case of relapsed MM with bilateral breast plasmacytomas and widespread EMD in a male patient, in whom contrast-enhanced mammography (CEM) served as the initial diagnostic tool.
Case presentation
A 73-year-old man with IgG kappa MM, diagnosed 1 year earlier following evaluation of lytic spinal lesions and bone marrow biopsy ( Fig. 9 ), presented to the breast clinic with new-onset gynecomastia and multiple palpable masses in both breasts and axillae.
He had previously received VCD (bortezomib, cyclophosphamide, dexamethasone), achieving a partial response.
Imaging: CEM low-energy images demonstrated multiple oval and irregular high-density bilateral breast masses (up to 7.5 cm), some with well-circumscribed margins and others with partially obscured margins, without associated calcifications ( Figs. 1 and 2 ). Recombined CEM images showed bilateral multifocal masses with heterogeneous internal enhancement and high conspicuity, raising suspicion for a hematologic malignancy. According to the BI-RADS lexicon, the findings were categorized as BI-RADS 4C. Ultrasound confirmed multiple hypoechoic lesions, predominantly circumscribed to mildly irregular, with minimal internal vascularity ( Fig. 3 ). Fig. 1 Contrast-enhanced mammography, mediolateral oblique (MLO) views of the right and left breast (low-energy and recombined images). Bilateral, multiple heterogeneously enhancing breast lesions are visible. Right-sided axillary lymphadenopathy is present. Fig 1 Fig. 2 Contrast-enhanced mammography, craniocaudal (CC) views of the right and left breast (low-energy and recombined images). Bilateral, multiple heterogeneously enhancing breast lesions are again demonstrated. Fig 2 Fig. 3 Breast ultrasound. Multiple hypoechoic lesions with well-circumscribed margins are identified in both breasts. Fig 3 Fig. 4 Contrast-enhanced CT of the liver. (A) Arterial-phase imaging shows hepatomegaly with multifocal hypervascular lesions distributed throughout both lobes. (B) No washout is observed on delayed-phase imaging. Fig 4 Fig. 5 T1-weighted MRI of the thoracolumbar spine demonstrates multiple hypointense lesions consistent with marrow infiltration. Fig 5





Histopathology: Ultrasound-guided core biopsy revealed sheets of atypical plasma cells with eccentric nuclei and prominent nucleoli ( Fig. 6 ). Immunohistochemistry demonstrated CD138+, CD56+, CD79a+, and strong kappa light-chain restriction; lambda was negative ( Fig. 7 ). Cytokeratin staining was negative, excluding carcinoma. Excisional biopsy of an axillary lymph node and core needle biopsy of a liver lesion confirmed disseminated extramedullary plasmacytomas ( Fig. 8 ). Fig. 6 Breast histopathology (hematoxylin and eosin stain). Infiltration of atypical plasma cells is observed within the breast parenchyma and adjacent mammary fat. Fig 6 Fig. 7 Breast immunohistochemistry (IHC) shows atypical plasma cells with strong membranous positivity for CD138. Fig 7 Fig. 8 Liver biopsy immunohistochemistry (IHC) demonstrates atypical plasma cells negative for cytokeratin (CK), supporting exclusion of carcinoma. Fig 8 Fig. 9 Bone marrow biopsy at initial presentation (hematoxylin and eosin stain) demonstrates infiltration by atypical plasma cells. Fig 9




Staging: CT demonstrated disseminated EMD, including multifocal hypervascular liver lesions, pancreatic and retroperitoneal masses, ascites, and new lytic bone lesions ( Fig. 4 ). MRI of the thoracolumbar spine demonstrated multiple marrow lesions consistent with disease progression ( Fig. 5 ).
Despite supportive care, the patient’s condition deteriorated, and he died 1 month later from progressive disease.
Discussion
Breast plasmacytomas are extremely rare, with fewer than 60 cases reported, and bilateral involvement in men is exceptionally uncommon [ [5] , [6] , [7] , [8] ]. Most cases occur at relapse or in refractory disease [ 9 ]. Imaging features are nonspecific and may resemble breast carcinoma, metastases from EMD, or lymphoma [ 10 , 11 ]. Although a few recent reports have illustrated the appearance of hematologic malignancies—particularly lymphoma—evaluated using CEM [ [12] , [13] , [14] ], published examples involving plasmacytomas or MM assessed with CEM are exceedingly limited. To our knowledge, this case represents one of the first descriptions of CEM findings in male breast plasmacytoma, underscoring the potential diagnostic value of CEM in detecting hematologic malignancies of the breast.
In this patient, CEM was particularly informative, demonstrating: (1) multifocal lesions with heterogeneous internal enhancement; (2) consistency between low-energy and recombined views, supportive of true enhancing masses rather than artifact; (3) correlation with ultrasound showing solid hypoechoic masses with minimal vascularity.
Histologically, the typical immunophenotype includes CD138+, CD56+, and light-chain restriction, consistent with aggressive MM biology [ 10 ].
The differential diagnosis of bilateral male breast masses includes gynecomastia, lymphoma, metastatic disease, and primary breast carcinoma. In MM patients, new bilateral breast lesions should prompt consideration of plasmacytomas, particularly in the context of suspected extramedullary relapse. This case underscores the importance of considering plasmacytoma in men with MM presenting with new breast lesions.
Conclusion
This case illustrates an exceptionally rare manifestation of relapsed MM: bilateral breast plasmacytomas in a male patient. CEM provided clear visualization of multifocal enhancing lesions and played a key diagnostic role. Recognizing this presentation is important for timely biopsy and staging, particularly in relapsed MM with suspected extramedullary disease.
Teaching point
In patients with relapsed multiple myeloma, new bilateral breast lesions—including in men—should raise suspicion for plasmacytoma. Contrast-enhanced mammography can clearly depict multifocal enhancement patterns and guide targeted biopsy.
Patient consent
Written informed consent could not be obtained as the patient is deceased, and relatives could not be contacted. Permission for publication was granted by the Riga East University Hospital Scientific Committee (Approval date: 8 September 2025; Reference No. 8-1/25/14).
Ethical Approval
This case report received confirmation of permission from the Riga East University Hospital Scientific Department. Written informed consent could not be obtained as the patient is deceased and relatives could not be contacted; permission for publication was granted by the hospital’s scientific committee.
Author Contributions
Ilze Eņģele: Concept and design, manuscript drafting, radiology image analysis. Tatjana Zablocka: Pathology image analysis, critical revision of manuscript. Evija Asere: Radiology image analysis. Jānis Eglītis: Supervision, final approval of manuscript.
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Competing Interests: The authors declare no known competing financial interests or personal relationships that could have appeared to influence the work reported in this article.
Acknowledgments: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.