This narrative literature review addresses the problem of an adnexal mass discovered during the course of breast cancer (BC) care, which may represent a benign condition, a metastatic process, or a primary ovarian cancer (OC), clinical scenarios associated with distinct physiopathology and prognosis. Furthermore, the coexistence of BC and OC in the same patient may be owing to a hereditary disorder, deserving specific management strategies and counseling. The initial detection and evaluation of an adnexal mass in a patient with BC requires a high index of suspicion, and the initial workup should include a thorough medical history and physical examination, measurement of tumor markers, complete blood count, and imaging tests. Transvaginal ultrasonography remains the standard tool, and findings suggestive of malignancy include bilateral tumors, thick septations, predominance of a solid component, Doppler flow to the solid component, and ascites. From the pathology point of view, features that are suggestive of metastatic disease include bilaterality, mild ovarian enlargement, vascular emboli, no omental deposits, and the absence of transition from benign to malignant epithelium. Although there is a considerable overlap in OC and BC immunohistochemical profiles, BC usually stain positive for GCDFP-15 and negative for vimentine, PAX8, and WT1, and OC often stain positive for CK7, PAX8, WT1, and to mesothelin. Genetic counselling should always be indicated in this clinical scenario. In conclusion, diagnostic spectrum of an ovarian mass in a patient with BC is broad, and a systematic multi-professional strategy is necessary to conduct these challenging cases.