Hello, I have a lump on the left side of my neck posteriorly, just below the head, I think it has been there for more than 5 years, it's not visible by looking at it, it's only visible when I bend my head forward a bit. Throughout these 5 years I didn't have headaches, or pain, I just feel a bit of pressure at that side of my neck like it's pretty obvious to me that the two sides of my head don't feel symmetrical. But recently I was able to feel that this pressure feeling is also going up to my head. How can I know if this lump is cancerous or not? Thank you.