I have a broken tooth and directly under it on the jaw line there is walnut sized lump pushing out near my neck. is this an abscess or cancer?

See your dentist: Tooth infection can cause that lump. You must check it with a dentist first to see what is next.

Possibly abscess but: See your dentist asap. If the tooth is severely broken, it will need to be removed. If the large swelling is an abscess, it will get larger and needs to be drained. You may require antibiotics. Only your dentist can tell exactly what you problem is and can appropriately treat it.

Likely abscess: Get to the oral surgeon immediately. Tell them just what you said in this question. You may be developing a cellulitis which can be life-threatening. Go now. If you cannot get to oral surgeon, go to er. Do not wait.