Aggressive lactating adenoma mimicking breast carcinoma
Highlights of the case
-Lactating adenoma is a benign “tumor of pregnancy” which typically occur in the third trimester or lactation period.
-In some cases, the clinical presentation of lactating adenoma might mimic breast cancer.
-Surgery to remove the tumor for careful pathological assessment might be required to confirm the diagnosis.

Lactating adenoma is a rare breast tumor which is commonly found in late pregnancy or lactation period. Despite its benign nature, lactating adenoma might develop aggressively and can be misdiagnosed as breast cancer.

A 25-year-old female came after noticing a rapid growing mass in her left breast for 16 weeks. On examination, the patient was afebrile and there were two large masses on her left breast with diameters of 20×7cm and 10×6cm, which was ulcerated and bleeding. A relatively fixed 2-cm lymph node in the left axilla was also noticed. On ultrasound, there were two heterogeneously echogenic lesions with irregular borders and fatty infiltrate, of which the diameters were about 10cm and 20cm respectively. Besides, several axillary lymph nodes with the largest diameter of 2cm were found, but the fatty hilum was still present.

Local dressing and pressure were applied to slow down the bleeding. Blood transfusion and prophylactic antibiotics were also indicated. The initial clinical diagnosis was cT4bN2M0 breast cancer. However, an open biopsy with local anesthesia was done which yielded the result of lactating adenoma of the breast. The tumor still significantly bled and palliative mastectomy was performed. During surgery, surgeons found two large tumors that had unclear borders and spread to almost entire breast tissue but did not invade the pectoralis muscles.

On post-operative pathological examination, there were necrosis areas along with breast ductal hyperplasia. The epithelial cells exhibited secretory changes which had mildly hyperchromatic, round nuclei and prominent cytoplasmic vacuoles (Fig. 2). The final diagnosis was then lactating adenoma. There were no post-operative complications, the axillary lymph nodes shrank gradually after antibiotic treatment and the patient was stably discharged two weeks later. The pregnancy then went well and she gave birth to a healthy girl after two months. After two years of follow-up, there have been no signs and symptoms of recurrence or metastasis.

In terms of treatment, since lactating adenoma has a low risk of recurrence, enucleation is the recommended therapy, especially in patients with ulceration and bleeding. Bromocriptine, a dopamine agonist to suppress lactation can be used preoperatively to reduce the size of the tumor

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