The presence of pain in cancer is not an uncommon phenomenon. However, the causes of pain in cancer are complex and characterized by diverse symptoms and diverse causes of development. There is a direct link between the two. When cancer presents with leg pain, the symptoms are extremely complex. There may be fever, leg fractures, and some cancers may be accompanied by leg swelling, color bruising or leg cyanosis, extremely severe varicose veins in the legs or pallor, numbness, and loss of sensation. Some cancers may occur with pain in certain areas, while others may have pain throughout the leg. Different causes of onset can also lead to a diversity of symptoms. Pelvic cancers may cause compression and embolism of the iliac vessels, the return vessels of the leg, causing vascular pain. Compression of the arterial blood vessels supplying blood to the legs may show some signs of inadequate blood supply, while compression of the main venous return vessels may cause bruising and swelling. Bone malignant tumors occurring in the lower extremities can directly cause bone erosion due to the action of tumor osteoclasts, and fractures can occur under weight-bearing conditions or with little force. Malignant tumors of the spine may cause radiating pain and discomfort in the entire lower limb due to direct compression of the spinal nerve root by the tumor. The causes of leg pain in cancer, that is, the characteristics of the primary disease can lead to the appearance of symptoms showing diverse characteristics.