Introduction Metastasis of the appendix is extremely rare. Breast cancer metastasis of the appendix is also a rare condition. Case presentation We are reporting the case of a 61-year-old female patient who was diagnosed with left breast cancer 3 years ago, underwent a modified radical mastectomy after neoadjuvant chemoradiotherapy. She received adjuvant chemoradiotherapy after breast surgery. Routine follow-up was normal after the treatment and presented with abdominal pain, nausea, and vomiting for 5 days. The patient underwent laparoscopic appendectomy with the diagnosis of perforated appendicitis. Histochemical examination revealed invasive lobular breast cancer metastasis and a positive surgical margin. Right hemicolectomy was planned for the patient, but the patient gave consent for the operation 4 months later. Surgery was discontinued due to widespread intra-abdominal peritoneal carcinomatosis in the exploration performed after the examinations. The patient was started on chemotherapy treatment. Appendiceal metastasis from breast cancer is rare and mostly occurs with perforation, if a second operation is required, it should be done early. Neoadjuvant chemoradiotherapy was given to the patient with the decision of the multidisciplinary tumor council. The patient is still undergoing chemotherapy treatment in the 6th postoperative month. Conclusion Acute appendicitis caused by metastasis from invasive breast carcinoma is extremely rare.