My mammogram was abnormal. what are the chances that i have breast cancer?

More than likely not: Abnormalities on mammograms are common. A radiologist can examine the mammogram and decide whether additional testing is indicated such as an ultrasound or a biopsy. You may also need a followup mammogram in a few months. 80% of the time, the finding on mammogram turns out to be benign.

Check BIRADS: Mammogram reports will include a birads category in an attempt to standardize interpretation. A birads 0 means that additional testing is needed, such as a magnification view or an ultrasound. Birads 3 means that the abnormality is "probably benign" (<2% risk) and warrants 6-month follow-up. A biopsy is recommended for birads 4 and 5 abn, which have a 15-30% and >75% chance of being malignant.

It depends: On how the lesion was categorized under the BIRADS classification, as outlined in another post. If you had a screening mammo and need extra views(BIRADS 0), 80% of the time it turns out to be nothing of concern, and of the remainder that go to biopsy, about 80% of those turn out benign.