I have ra, i had a mass on my chest, so they did ct-guided needle biopsy where the thymus is! doc has told me its not sarcoid, but could be lymphoma?

Wait for result: Yes, lymphoma is a possibility. There is also relationship between autoimmune disorder like rheumatoid arthritis and certain type of lymphoma. However, i recommend you to wait until you have the result of the biopsy then you can discuss further in detail about what to do.

Thymus: May be the source of the mass, and it could be invasive ornon-invasive. Thymomais associated with rheumatologic/auto-immune conditions. Lymphoma is another prospect, more rare are germ cell tumors (teratoma) and substernal thyroid. Sarcoid can involve any node bearing areas.