My mom had a tumer in the left leg(upper tibia). biopsy has been done. what could it be?

Many possibilities: You mother could have a primary bone lesion or a metastatic bone lesion. Correlation with the x-ray findings is essential for a correct diagnosis. Primary bone tumors include Osteochondroma,Giant cell tumor,Osteoid osteoma,Osteoblastoma and Enchondroma. In my experience more often than not a bone lesion is a metastatic lesion, a tumor that has traveled from somewhere else. Biopsy results soon.