An mri in nov 2012 showed a radiological cyst on l. femur; pain since may 2012. i have stage 111c breast cancer. should i get a pet /ct?

Should see doc ASAP: I am sorry to hear of your breast cancer status. Mri picture is only a picture. Regardless of what it is, it is causing you pain and that should be evaluated and treated. Maybe it is a cyst, or maybe it is something else. You have reasons to get it looked at more thoroughly and so please don't hesitate to consult your doc. Good luck to you.

Probably not: On mri, cysts are pretty easily distinguished from metastasis from breast cancer. If you still have concerns, ask your oncologist if he can have the MRI interpreted by a second radiologist to make all are in agreement with the cyst diagnosis.

PET/CT may not: Help much, but please see your doctor and complete the workup. If the first MRI did not include IV contrast, then a repeat MRI with contrast may be helpful. Also, what did the cyst look like on plain radiographs (x-rays) or a ct? You need to get an answer to your pain as well as a definite answer about whether the bone cyst could be cancer. Please get a full workup for the answers.