This patient self-detected the lump in her third trimester of pregnancy, and since breastfeeding, the lump got larger. The differential diagnosis was fibroadenoma, hamartoma and lactating adenoma.

The patient underwent an ultrasound-guided core biopsy. 

Histopathology

MACROSCOPIC DESCRIPTION: Four tan needle cores 3-14 mm. 

MICROSCOPIC DESCRIPTION: The sections show core biopsies of fibrofatty breast tissue containing benign breast lobules demonstrating lactational change. There is no evidence of dysplasia or malignancy.

CONCLUSION:
Breast, left, 5 o'clock core biopsy: Lactating adenoma (nodular lactational hyperplasia).