I have a Tumor growing out of my joint in my left shoulder iv had a MRI and it's say they can't rule out synovial sarcoma and since the MRI 3 months a?

Question? What is your question here? Have they done a biopsy? I know this is worrisome for you. Remember that you have right as patient to ask and see the MD who ordered the MRI in order to get all questions answered!
Possible malignancy. Tumor growing out of a joint is an abnormal lesion that must be defined by bx first and depending on finding, definitive treatment. Synovioma is not an uncommon lesion related to joint space. If lesion completely resected, cure is high. If incomplete resection then recurrence has poor prognosis. Should lesion be malignant then procedure of choice is Tikhoff Lindberg resection.