I had this happen to me in February this year and had the lump removed. Until they did a test they did not know what it was. It turned out to be Aspergillas which I know caused a great deal of interest from the staff as it is not known how on earth I had got it. Anyway I am doing fine now. my Breathing is still rubbish but I don't seem to be getting as many infections as I was before and my weight which I lost seems to be going back on at last.
I know it is scary when they say lump or mass but 9/10 times it turns out to be something they can do something about.
Why not try and contact your consultant who can reassure you.
I will say I was treated extremely quickly so hopefully you wont have long to wait. I was treated at Guys and they were great so good luck to you and best wishes.