What Causes Milk Production In Non Pregnant Woman After Lumpectomy?

my aunt was recently diagnose with invasive ductal carcinoma on her left breast so they did a mastectomy on the left. the right breast was diagnosed with fibroadenoma with fibrocystic changes. she had a lumpectomy on the right. on her follow up appt, they aspirated 70cc of milky fluid out of the right breast, not pus as she is asymptomatic for an infection. what could cause milk production as she is not pregnant or nursing?