To determine whether leg pain is caused by lung cancer, it is necessary to identify from several aspects: 1. medical history, it should be clear when lung cancer occurs and the time sequence of leg pain, if there is recurrent leg pain first and then lung cancer, then there is no connection between the two; 2. Check whether there is any metastatic sign of lung cancer, if there is no sign of distant metastasis, the leg pain is not related to lung cancer; 3. If there are metastatic signs of lung cancer, see whether there is lumbar spine metastasis or bone metastasis in lower limbs, CT of lumbar spine, magnetic resonance, whole-body bone imaging scan, etc. If there are metastasis of these bones, the pain may be caused by spinal nerve compression due to metastatic cancer, or the pain is caused by bone metastasis in lower limbs. To determine whether leg pain is caused by lung cancer, it is recommended to consult a specialist and be determined by a professional physician after combining various aspects of assessment.