LAUSR

Introduction and importance A lactating adenoma is a benign breast tumor occurring in young women during pregnancy or lactation. Its growth is usually slow but, occasionally, can become rapid, resulting in a giant mass. This case report outlines an example of the rapid growth of a lactating adenoma, which was surgically excised. In this case, malignancy could not be ruled out, and biopsy and surgical excision were considered. Case presentation We present the case of a 28-year-old woman referred to us owing to the presence of a left breast mass with progressive enlargement. She initially presented with a left breast mass of approximately 20-mm in size, which increased to an approximate size of 70 mm during pregnancy. The patient's mammogram showed an equal-density lobular mass in the left breast. Ultrasonography and magnetic resonance imaging revealed a circumscribed lobular mass with cystic regions in the upper lateral quadrant. The patient was diagnosed with adenosis using core needle biopsy. However, it did not shrink during follow-up, and resection was performed. Histologically, the proliferation of the cystic ducts containing eosinophilic secretions and dilated tubules consisting of cuboidal or hobnail-shaped cells were observed. Clinical discussion Lactating adenoma, phyllodes tumor, and breast cancer are essential differential diagnoses when the size of breast masses increases rapidly. Ultrasonography is the first choice to examine lactating adenomas. Echogenic bands and pseudocapsules are characteristics of lactating adenomas. Conclusion Surgical excision is a notable treatment option when a lactating adenoma exhibits rapid growth or increase in mass, as it could be malignant.