Abstract: A 61-year-old patient was admitted in November 2024 with the chief complaint of “marked enlargement of uterine myoma for 2 months after menopause”. This patient was diagnosed with uterine myoma 8 years ago and underwent modified radical mastectomy for right breast cancer in April 2023. Postoperative pathology revealed invasive carcinoma (SBR grade Ⅲ). Upon admission, examination results showed a cystic-solid mass in the posterior wall of the uterus and an elevated CA153 level of 273 U/mL. Transabdominal total hysterectomy and bilateral adnexectomy were performed. HE staining postoperatively indicated uterine myoma with involvement of invasive lobular carcinoma. Immunohistochemistry showed positivity for pan-cytokeratin (CKpan, ＋), GATA3 (＋), desmin (muscle＋), and estrogen receptor (ER, 90%＋ ＋ ＋), confirming the diagnosis of breast cancer metastasis to the uterine myometrium. CDK4/6 inhibitor, anastrozole, and zoledronic acid were used after surgery. Metastasis of invasive lobular carcinoma to the uterine myometrium is rare. Rapid enlargement of uterine myoma in breast cancer patients should alert clinicians to consider the possibility of metastasis, which must be confirmed by pathological examination.