A 52-year-old woman presents to her GP with a 6-week history of a painless lump in her left breast, which she noticed while showering. She reports that the lump has gradually increased in size but denies any associated pain, discharge, trauma, or systemic symptoms. She is postmenopausal, has two children, and has no history of hormone replacement therapy. There is no known family history of breast or ovarian cancer. Her last mammogram was over five years ago. She is otherwise well and takes no regular medications.