[A Case of Invasive Lobular Carcinoma Complicated by Disseminated Carcinomatosis of the Bone Marrow with Severe Bone Marrow Fibrosis and Acute Splenomegaly].

A 60-year-old female presented at our hospital with a mass in her left breast. Needle biopsy of the breast mass confirmed a diagnosis of invasive lobular carcinoma, and the patient underwent left mastectomy and axillary lymph node dissection. The patient received adjuvant chemotherapy and was started on continuous endocrine therapy. Three years post-surgery, she experienced recurrence of multiple bone metastases and received a combination of hormone therapy and selective cyclin-dependent kinases 4/6 inhibitors. Therapeutic efficacy was poor, allowing bone metastases to spread. Four months post-recurrence, blood tests revealed moderate thrombocytopenia. Despite the switch to chemotherapy, the patient's platelet count did not recover. CT revealed splenomegaly, which was not present three months earlier. Bone marrow biopsy revealed severe myelofibrosis with infiltration of small dysplastic cells into dense fibrotic tissue. The patient developed microangiopathic hemolytic anemia, but DIC was not observed during the course of the disease. Ten months after recurrence, a brain metastasis was detected, and the patient died the following month.