Hi and welcome to Mayo Connect
Hyperechoic masses in the breast are cancerous < 0.04% of the time.
CT addresses possible metastisis in breasts cysts. "No metastasis" doesn't indicate the possibility of malignancy.
But you have no metastasis which is good.
Your mass has grown 1 cm in five years.
It is less than the size of a grape, but larger than a single peanut seed.
You have a lymph node that has a thickened cell wall. Normal is 3 yours is 3.5
Did you have a needle biopsy? Often they will drain a cyst after a biopsy determines it to be benign.
You might call your medical provider and request biopsy and drainage.
I'm assuming you had the melanoma removed. You may be due for a skin exam.
I have no medical expertise. But can say that something is making you sick, because you are feeling sick.
It could be completely unrelated to the cyst or the melanoma. But it is important to find out.
Don't be discouraged from contacting us here. Tell us your symptoms. Someone may have the exact same symptoms and know exactly what is causing them.
Meanwhile contact your medical providers.
Bless your health.