Could you get breast cancer after a mastectomy?

Yes: There could be residual malignant breast tissue in the chest wall (local recurrence) or the cancer could have already spread to other organs before surgery (metastasis).

Yes: During a mastectomy, the surgeon attempts to remove as much breast tissue as possible but no surgeon can remove every last bit of breast tissue. Your residual skin/surrounding tissue still has to remain viable. So even with a double mastectomy (removal of both breasts) there is still a very small chance of developing breast cancer at a later time.