You were told a lot before your cancer treatment. Surgical margins. Chemotherapy cycles. Radiation fields. Side effects, recovery times, follow-up schedules. What you probably weren’t told, in any detail, is how your lymphatic system works — even though a piece of it was likely removed or irradiated, and even though understanding it turns out to matter enormously for the rest of your life. This article is the explanation you should have had. Not advice first — the anatomy first. Once you understand what this system does and what treatment did to it, most of the advice you’ll encounter makes sense on its own, and you’ll be able to tell the good advice from the outdated kind.