Is it possible breast cancer recur even after mastectomy?

If the treatment for the original tumour leaves even one cell alive that cell can keep on surviving in the body. If it finds a welcoming spot in the body – one where it has access to a blood supply and can evade the immune system – it can keep growing and dividing into two daughter cells, repeating the process until it eventually seeds a whole new tumour in a new location.
For breast cancer, the new location is often the bone, liver, or brain – other cancer types will spread to other locations. This phenomenon is seen in many different types of cancer, not just breast. The disease can seem to reappear after such a long time because it can take a very long time for the cell to create a new tumour that’s big enough to cause symptoms or show up in medical scans. The cells that develop resistance to chemotherapy drugs aren’t always the ones that grow the fastest – in fact, it might be in part a slow growth rate that protects them from the effects of the drug. So the cell was there all along; it just wasn’t noticed.