Schwannoma of the Appendix Mimicking a Metastatic Breast Cancer: .

Metastatic breast cancer (MBC) represents 5-10% of newly diagnosed breast cancer cases, referred to as de novo stage IV MBC. Distinguishing a distant lesion in breast cancer patients can be challenging. Therefore, obtaining a histopathological confirmation of a metastasis is advisable, as a suspicious metastatic lesion may be benign or exhibit different immunohistochemistry compared to the primary site. We report a 55-year-old female patient who presented to a tertiary care hospital in Muscat, Oman in 2019. The patient was undergoing staging scans for newly diagnosed breast cancer, where radiological findings suggested appendix metastasis. However, subsequent laparoscopic appendicectomy revealed an appendicular schwannoma, confirmed through immunohistochemistry. The patient received curative-intent breast cancer treatment. With the increasing use of advanced staging scans in breast cancer, clinicians should thoroughly investigate and confirm metastatic disease, especially in uncommon metastatic sites, before initiating treatment.