I have a hard immovable lump behind my right ear for 4 wks. doc said its a lymph node and referred me to ent. i am concerned- could this be cancer?

May or may not be!: Enlarged lymph nodes are commonly due to infection or inflammation. In such cases the node is tender to touch/pressure. Painless lymph nodescan be due to cancer but it depends on their size and whether node is growing in size over a period of month or two. But you need an exmaination from your doctor who will do a biopsy if the node is suspicious for Cancer. Without a biopsy we're all guessing.