Triple‐Negative Breast Cancer Presenting as Recurrent Cystic Lesions During Lactation: A Case Report

Lactation-associated breast cancer poses diagnostic challenges due to physiological breast changes that may mask malignancies. Triple-negative breast cancer (TNBC) during lactation is rare and aggressive, requiring vigilant evaluation and treatment. This report highlights the diagnostic dilemma of recurrent cystic breast lesions during lactation, which can mimic benign conditions like galactoceles but may conceal aggressive TNBC, leading to potential delays in diagnosis despite initial conservative approaches such as aspiration. A 26-year-old lactating woman presented with recurrent complex cystic lesions initially mistaken for benign lactational changes. Despite multiple aspirations, the lesions enlarged, leading to surgical excision. Pathology confirmed TNBC (ER-, PR-, HER2-, Ki-67 ~40%). Core needle biopsy and extended resection with sentinel lymph node biopsy confirmed grade III invasive ductal carcinoma. The patient received 8 cycles of chemotherapy (4 cycles of pegylated liposomal doxorubicin and cyclophosphamide, followed by 4 cycles of taxane) without radiotherapy, achieving 6-year recurrence-free survival. Persistent complex cystic lesions during lactation require core needle biopsy to rule out malignancy. Multimodal TNBC treatment can yield favorable outcomes, including fertility preservation, as evidenced by the patient's subsequent pregnancy in 2024.