Hi!
I'm very sorry for your sister . How old is she?
At the time of diagnosis, most of the patients have micrometastatic disease, but isn't detectable. Tumor, usually, spreads to the lungs and rarely results in respiratory symptoms. I don't wanna sound negatively, but osteosarcoma should be regarded as a metastatic disease, even when only a single primary lesion is found. That's why most of the doctors are suggesting chemotherapy before performing a surgery to remove the primary tumor.
Please, keep me updated !
All best to you and your family!
Marija