I am 20 years old, and several weeks ago, I noticed there is a soft lump on my penis. It is located on top of the penis shaft, and slightly to the right of the center of my shaft. The lump seem to be under the skin, and it can only been seen when my penis is flaccid and foreskin pulled back (I am uncircumsized). It is soft to the touch, not firm at all, it is almost gel like, but i can feel distinct border at one of the side. I believe it is dark in color (it kind of look like dark blue).
It is kind of hard to describe the size of the bump, since sometime I can see it bulging out alot when flaccid, but sometime i only see it bulging out very little (I think it may be due to how flaccid my penis is at the moment). But some observation I noticed are that, sometime if i pull my foreskin completely back (completely back as in you would normally not pull that far back), the bump may become flat, but I do still see the color, and it is shaped like a backward "u". The bump seem to be completely gone when my penis is erect. I am not quite sure if the color still there when my penis is erect, because bottom part of my penis has a darker tone color.
From lot of research, I think one possible reason is penis vein thrombosis, that or penile cancer (according to this question from medhelp:
http://www.medhelp.org/posts/show/226754)
1) I would want to know from the description above, what is the chance of it being cancerous, and what is the chance of it being thrombosis or other disease. Is there any way to distinguish these diseases, without going through ultrasound or other instruments (maybe penile tumor is hard, solid mass?)
2) Also in some website, I saw some symptoms of thrombosis is firm, solid bump. Would thrombosis also occur as soft lump (like mine) and in my location (on top of my penis shaft).
Thank you for your help