If someone has osteosarcoma in their thigh, will he feel a bone lump before it spreads to a lung?

Not necessarily. The majority of patients with osteosarcoma present with localized pain, usually of several months' duration. At the time of presentation, between 10 and 20 percent of patients have macrometastatic disease, usually to the lungs or bone. Occult micrometastases are presumed to be present in the majority of patients who appear to have localized disease.