Like @Tennille I felt really healthy and had no signs or symptoms when I was diagnosed with metastasis 11 years after my initial breast cancer. I noticed an enlarged supraclavicular (above collar bone) lymph node, went to my GP, had a biopsy, results came back as metastatic breast cancer. I then had CT scans and bone scans which showed bone and lung metastasis. After 11 years I had almost stopped worrying about my breast cancer returning - but there are no guarantees with this awful disease, and you need to investigate anything unusual that you notice.