A 61-year-old woman was diagnosed with breast cancer [T3N3cM0: Stage IIIC, estrogen receptor [ER] (+), progesterone receptor [PgR] (+), human epidermal growth factor receptor 2[HER2] (-)]at the time of initial presentation. Following diagnosis, combined modality therapy including hormone therapy and chemotherapy were initiated, but hemorrhage from the primary lesion and bone metastases were observed. Priority was given to treatment of the breast cancer, and chemotherapy was administered, after which, right mastectomy and axillary lymph node sampling were performed to assess local disease control. In addition, concurrent right kidney enucleation was performed for a renal lesion. The renal neoplasm was diagnosed as T1aN0M0, Stage I. After this intervention, treatment of the breast cancer was continued, but pain of the right femoral region developed, and bone metastasis was diagnosed on close inspection. The bone metastasis was considered to derive from the breast cancer. During hospitalization, the patient fell and broke her right femur. Open reduction and internal fixation was performed immediately, and bone metastasis of kidney cancer was diagnosed via perioperative cytodiagnosis. Pulmonary metastasis, local recurrence, and metastasis to the shoulder blade have been detected. The metastases are considered to derive from the breast cancer, for which treatment has been continued. In the case of concomitant cancers, biopsy for metastatic foci can be considered essential, whenever it can be performed safely.