HER2-Positive Breast Cancer Treatment Followed by Multiple Myeloma

What happened, in summary

A 56-year-old woman was diagnosed with Stage II HER2-positive cancer of the left breast after finding a painless mass. Ultrasound showed a breast tumor measuring about 2.6 cm and suspicious left axillary lymph nodes. Biopsy confirmed grade II invasive breast carcinoma of no special type, with ER-negative, PR-negative, and HER2 3+ results. She began neoadjuvant chemotherapy together with HER2-targeted pertuzumab and trastuzumab. Low platelet counts complicated treatment and led clinicians to adjust the chemotherapy regimen. After 6 cycles, imaging and clinical assessment showed a partial response. She then underwent breast-conserving surgery with sentinel and axillary lymph node surgery. Pathology found a very small invasive focus remaining in the breast and cancer in 1 of 13 removed axillary lymph nodes. She received 4 additional cycles of pertuzumab and trastuzumab and completed 28 fractions of radiation to the breast and supraclavicular area. Follow-up breast imaging, chest CT, and bone scan showed no recurrence or distant metastasis. Months later, she developed fever, anemia, and persistent low blood counts. Further testing identified a separate IgA-lambda multiple myeloma. Her breast cancer was still described as stable at that time, and she was transferred for treatment of the blood cancer while continuing follow-up for her breast cancer history.