I have metastatic breast cancer to my bones. i just had pleural effusion in my lungs. at the same time, my oncologist did a ca27-29 test and it's 5,000. normal is under 40. is this possibly from the effusion? i've had a lot of trouble breathing?

From the info you provided, elevated CA 27.29 is obvious because you have metastatic breast cancer. Pleural effusion in your case is most likely a malignant effusion and if the CA 27.29 was lower before even with bony metastases but now it is elevated, it points out the malignant effusion, a new metastatic source, is the culprit. Pleural effusion causes dyspnea, especially in supine position.

It's not just the malignant pleural effusion but the widespread breast cancer cells producing these markers. It appears that more of the pleural fluid has to be removed to alleviate your dyspnea. Insertion of talc powder may be advised in an effort to prevent reaccumulation of effusion after it's removed. Your oncologist will provide you good care.