Occult breast cancer usually presents as axillary metastases without breast involvement in imaging studies and without evidence of malignant histological lesions in the mammary gland. Of the new cases diagnosed each year it represents between 0.3 and 1%, and the incidence has not decreased despite advances in imaging tests. This also contributes to the lack of experience and controversy in the treatment of this condition. A 62-year-old patient, with no personal or family history of risk, was referred to our clinic in March 2022, for evaluation for suspected lymph node metastatic disease. An axillary ultrasound was performed that revealed a lymph node plastron in the left axilla, for which an ultrasound-guided axillary biopsy was performed, using a 14-gauge cutting needle, and concluded with the histological and immunohistochemically diagnosis of metastasis of primary adenocarcinoma of the mother. Additional studies performed, mammography, breast ultrasound, and breast MRI, did not reveal the presence of a primary tumor. With the diagnosis of cToN2Mo left occult breast cancer, stage III A, luminal A, neoadjuvant treatment with chemotherapy was scheduled, which ended in January 2022 and was followed by surgery, which consisted of an axillary dissection of levels I and II. With the pathology results, we concluded with a diagnostic impression of ypToN3Mo stage III C, luminal A breast cancer. She was referred to the radiotherapy service, where external radiotherapy was ordered, to the left mammary gland and lymphatic drainage areas, completing the treatment. in November 2023. Last evaluation in consultation, in February 2024, there was no clinical or imaging evidence of local or distant recurrence. He is currently receiving adjuvant systemic therapy with anastrazole 1 mg.

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