<s>[INST] I have noticed that I have a large bump on my armpit. I would say it is almost the size of a golf ball. There is not really any pain, but I have just noticed it 2 days ago. I recently found out that i have hyperthyroidism, and a month ago took the radioactive iodine pill treatment. Could that be a reason why? [/INST] Welcome to Chat Doctor .1. In this case pain less lump in the armpit (axillary region) are lymph nodal enlargement.2. Lymph nodal enlarge net could be infection / inflammatory reactions in the body.3. It could be one of the reason for sure, as any systemic disease can cause enlargement.4. See your doctor and ask for alternative medication and see.5. If still not resolving - you need to get a biopsy get done to find out the cause. Hope it helps you. Anything to ask ? Do not hesitate. Thank you. </s>