What does "probably benign" mean on a mammogram report?

Most likely normal.: While mammograms are excellent screening tests for cancer, they are not perfect. Many times spots are seen on mammography that are not normal but have such a low probability of being cancer (<0.5%), that it is best to watch these closely rather than biopsy. Radiologists categorize this as a birads-3 abnormality; when women get their first mammogram, there is a 7% chance this will happen.

6-month follow-up: Usually this is a lesion that has a very low risk of malignancy that the mammographer wants to follow closely (typically at 6-months, but sometimes sooner). According to the birads manual, the system radiologists use to manage mammography patients, the radiologist should think there is <2% risk of malignancy. In reality, the actual risk of malignancy is <1% (0.5-0.8 are numbers I have seen quoted).

Probably benign: In terms of BIRADS categories, it is category 3, technically less than 2% chance of cancer, but in practice it is less than 1%. Usually short interval follow up is recommended.