So I didn't know (or maybe I kind of knew and was pretending I didn't) that some cancer cells go hide in your body to come out later as metastases. However, current research has been working on this issue.
“…researchers have discovered the conditions by which specific signals in primary tumors of head and neck and breast cancers can pre-program cancer cells to become dormant and evade chemotherapy after spreading.”
“Recurrence of cancer after initial treatment remains a critical unsolved problem for too many patients,” said William Oh, MD, Chief, Division of Hematology and Medical Oncology, and Professor of Clinical Cancer Therapeutics at The Tisch Cancer Institute, Icahn School of Medicine at Mount Sinai. “This highly innovative research provides a novel path forward for targeting dormant cancer cells which may be 'hiding' from our available therapies and which may need additional drugs to root them out and improve cure rates.”