Breast biopsy needed, abnormal cells in bloody aspirate from a cyst. can no longer be found on u/s should i have an mri or leave it? birads 3

Do not ignore: Mri first. If localised open biopsy, if not follow up in 4-6 months.

Repeat the ultrasoun: If a bloody cyst is pathologic, it will reaccumulate rather quickly. Nonetheless, if repeat u/s (2-4 weeks after aspiration) does not show a cyst/or remnant of a cyst, it is unlikely that an MRI will reveal an abnormality and only lead to additional testing, because of the lack of specificity. I would wait and follow with ultrasound again in 3 months.