What happened, in summary

This 68-year-old man was diagnosed in September 2016 with Stage I infiltrating ductal carcinoma of the breast, pT1N0M0. The tumor was estrogen receptor-positive and progesterone receptor-positive, with Ki-67 of 30%. FISH testing showed HER2/CEP17 ratios below the diagnostic threshold. Initial treatment included the TAC chemotherapy regimen and letrozole. Two years later, he developed bone pain, and bone imaging showed multiple osteolytic lesions in the ribs and ischium. Bone biopsy was recommended but refused, so the lesions were treated as likely breast cancer metastases. His treatment was adjusted several times, including letrozole plus everolimus, anastrozole plus neratinib, gemcitabine plus capecitabine, paclitaxel plus anlotinib, denosumab, fulvestrant plus everolimus, and radiotherapy. Bone pain and osteolytic lesions continued to worsen. In May 2021, he developed fatigue, nausea, vomiting, renal failure, hyperkalemia, and coin-shaped cells on peripheral smear. Testing showed IgG-kappa monoclonal gammopathy, very high free kappa light chains, abnormal plasma cells in bone marrow, and IgH rearrangement, leading to a diagnosis of multiple myeloma. He received VDD, then IDD because of neuropathy, then DRD with partial response. In April 2022, he developed a large hemorrhagic pericardial effusion, drained by pericardiocentesis, with cytology concerning for malignant cells. KBD therapy improved dyspnea and reduced the effusion; 4 cycles produced very good partial response. He underwent stem cell collection and autologous hematopoietic stem cell transplantation with engraftment, but later died from a novel coronavirus infection. The breast cancer and plasma-cell disorder overlapped clinically because both can involve bone. This made careful interpretation important: several treatments targeted presumed breast cancer progression before the later laboratory and marrow findings clarified the diagnosis of IgG-kappa myeloma.