Multiple myeloma presenting as bilateral breast lumps in pregnant woman

Background Multiple myeloma (MM) is a systemic disease in the elderly. Its incidence in patients younger than 40 years old and especially in pregnant women is extremely rare. MM may involve extraosseous sites, and only in rare cases it is observed in the breast. Case report We describe the case of a 39-year-old woman diagnosed with an IgG lambda light-chain MM (Durie-Salmon stage IIIA, International Staging System II) in the 26th week of pregnancy, presenting with bilateral breast lumps. Dexamethasone (20 mg/m 2 /day on days 1–4, 9–12, and 17–20) was given as an induction agent to decrease tumor mass during pregnancy. Adverse response to dexamethasone was minor with excellent tolerance. A healthy baby was delivered at week 34 of gestation. Conclusion Breast nodules revealing MM are extremely rare. Clinical and radiological features are atypical. Presentation during pregnancy is extremely rare, making anti-MM treatment potentially challenging.