What is the likely diagnosis for a breastfeeding woman with a unilateral tender breast mass involving and attached to the areola, accompanied by many small cysts?

Lactating Adenoma

The most likely diagnosis is lactating adenoma (Option D), a benign breast mass unique to pregnancy and lactation that characteristically presents as a unilateral tender mass in breastfeeding women and may contain multiple small cysts on imaging. 1

Clinical Reasoning

Why Lactating Adenoma is Most Likely

• Lactating adenomas are masses unique to pregnancy and lactation, representing one of the most common benign palpable masses in breastfeeding women alongside galactoceles 1

• The clinical presentation matches perfectly: unilateral tender mass in a breastfeeding woman, with involvement of the areolar region and multiple small cysts 1

• These lesions can appear atypical on imaging due to hormonal stimulation causing proliferative and lactational changes, which may lead to concerning features including cystic components 1

• Lactating adenomas are sometimes interpreted as a variant of fibroadenoma and can naturally disappear at the end of pregnancy or lactation 2

Why Other Options Are Less Likely

Duct Ectasia (Option A):

• Duct ectasia typically presents with nipple discharge (spontaneous, unilateral, from single duct), noncyclical breast pain described as burning sensation behind the nipple, and is most common in women in their fourth decade 3, 4
• It is frequently associated with heavy smoking and affects 17-36% of pathologic nipple discharge cases 4
• The presentation described lacks the characteristic nipple discharge and burning pain typical of duct ectasia 3

Intraductal Papilloma (Option B):

• Intraductal papillomas are a common cause of bloody nipple discharge rather than presenting as a tender mass with cysts 4
• These lesions form within large lactiferous sinuses and typically present with pathologic nipple discharge (spontaneous, unilateral, single duct, serous or sanguineous) 1, 5
• The absence of nipple discharge in this case makes papilloma unlikely 1

Fibroadenoma (Option C):

• While fibroadenoma is the most frequent lesion found during pregnancy and lactation, it typically presents as a well-circumscribed solid mass rather than one with "many small cysts" 2
• Fibroadenomas can enlarge during pregnancy due to hormonal stimulation but are characteristically solid on imaging 1, 2
• The multiple small cysts described are more characteristic of lactating adenoma 1

Critical Management Considerations

Immediate imaging is essential:

• Ultrasound is the first-line imaging examination in lactating women due to young patient age and decreased sensitivity of mammography in dense breast tissue 1
• Over 80% of palpable masses biopsied in breastfeeding women are benign, but evaluation should not be delayed 1

Conservative management is usually appropriate:

• Management is typically conservative after triple assessment (clinical exam, imaging, biopsy if needed) 2
• Excisional biopsy is only mandated if the mass is rapidly enlarging or if there is discordance in the triple assessment 2

Critical pitfall to avoid:

• Do not delay imaging evaluation assuming all masses in lactating women are benign, as pregnancy-associated breast cancer (PABC) can present with a falsely benign appearance and has more aggressive biology 1
• If imaging shows suspicious features (BI-RADS 4-5), core needle biopsy is mandatory regardless of the clinical suspicion for benignity 1