How can you. tell the difference between fibrocystic breasts and breast cancer?

Tissue biopsy: Definitively, pathology evaluation on tissue biopsy of the breast will differentiate fibrocystic disease versus breast cancer.

Exam,Mamm,(sono)Gram: Fibrocystic changes may interfere w/breast examination and/or mammography. Nevertheless, using these modalities along w/breast ultrasound, we can usually distinguish between the two. Rarely, we need to check an MRI or even do a breast biopsy to evaluate a suspicious lump or mammographic abnormality.

Biopsy: If you have a discreet lesion or abnormality by radiographic imaging, then a core biopsy should be able to differentiate between fibrocystic changes and a malignancy.