Hello and welcome to MedHelp's forums. First, please know that demographically, your age means you are less likely to have breast cancer. Wanted to start with that fact. But when we find a lump under our arm pit, it's always wise to get it checked by your doctor. I would highly suspect that it is actually a lymph node and related to cancer as to why it is swollen. https://www.webmd.com/a-to-z-guides/swollen-glands#1. These swell in relationship normally due to the lymphatic system fighting off some sort of bacteria. It could also be a cyst.
So, to be sure, please let your doctor see it. If a triggered lymph node due to your bodies immune response in fighting off a cold or infection or other virus, it may last for several weeks.
Let us know what the doctor says but would not be overly worried.
Hello, wanted to follow up. I do think you should investigage the cyst. Often, a doctors office will aspirate those. Did they recommend any further follow up for you? Here is everything you ever wanted to know about cysts! https://www.webmd.com/skin-problems-and-treatments/guide/cysts-lumps-bumps#1. Mostly they are not a cause for concern and do present the way yours did. However, you do need to make sure and this is why a doctor often will aspirate or do further investigation. So, it would make sense to follow up with your doctor about the cyst since it is changing. Let us know how this goes! Best of health to you.