Multiple Myeloma Presenting as Breast Metastasis: Diagnostic Challenges and Case Analysis

Area of Science:

• Oncology
• Hematology
• Pathology

Background:

• Extramedullary disease (EMD) signifies advanced multiple myeloma (MM).
• Secondary breast involvement in MM is exceptionally rare.
• EMD in the breast poses diagnostic challenges due to similarities with primary breast cancer.

Purpose of the Study:

• To report a rare case of secondary breast involvement in multiple myeloma (MM).
• To discuss the diagnostic difficulties and clinical management of this rare presentation.

Main Methods:

• Case report of an 83-year-old female patient with a history of immunoglobulin A (IgA) kappa multiple myeloma.
• Diagnostic workup included mammography, magnetic resonance imaging (MRI), and histological analysis with immunohistochemistry.
• Histological revision was performed due to discordant findings.

Main Results:

• The patient presented with multiple bilateral breast lesions.
• Initial histology was misinterpreted as primary breast carcinoma; subsequent review confirmed MM breast localization.
• Tumor cells expressed IgA kappa and MUM1, negative for hormonal receptors, HER2, and AE1/AE3 cytokeratin.

Conclusions:

• This case underscores the rarity of extramedullary multiple myeloma in the breast.
• Accurate diagnosis is challenging, requiring careful histological and immunohistochemical evaluation.
• Management is complex due to limited evidence-based data for this rare condition.