Rationale: Breast cancer is the most commonly diagnosed malignancies in females. The most common sites of metastasis are bone, lung, liver, and brain. Gastrointestinal and adrenal gland metastasis from breast cancer are rare. Simultaneous metastases are extremely rare. Therefore, it is critically important to choose proper examination and treatment since the rapid diagnosis and primary treatment can significantly affect the survival of patients. To the best of our knowledge, this was the first case of initial dual metastasis. Patient concerns: The patient had a history of left breast cancer, and she underwent left breast-conserving surgery with sentinel lymph node biopsy 2 years ago. She was hospitalized in our center with the complaints of a stomach and lower back pain, which started suddenly and was progressively increased for half a month. Diagnosis: Computed tomography, gastroscopy, and immunohistochemical staining, especially GATA3 and mammaglobin, confirmed that there was simultaneous gastric and adrenal metastases. Interventions: She was eligible for the IMpassion131 clinical trials, a Phase 3 randomized, double-blind, placebo-controlled trial under treatment with atezolizumab/palcebo plus paclitaxel as adjuvant-therapy. Outcomes: She was still undergoing the therapy and waiting for the further evaluation. Lessons: In order to better understand metastatic pathways of breast carcinoma, publications of individual patient cases diagnosed with rare metastatic sites should be encouraged, especially for the simultaneous rare metastatic sites. This might improve our understanding of metastatic behavior of breast cancer and promote further clinical research.