It could be several different things, but a doctor will have to take a sample and test it to know what it is. It could be a benign tumor. [I have something like that near my shoulder, not lemon-sized yet, but it keeps growing over the years.] If it is a benign tumor, it may be a good idea to have it removed because they can turn malignant without warning, or it can grow so large that it is debilitating and needs removal.
5'10" is the average size of an 18 year old bodybuilders bicep.
32
15
== ==
17.5"
30 inch
The size of an iron lump is about the size of an elephant child when it is newly born.
24 inch
.16.5
16 inches
18 inches
16 may be