What is metastasis and at what stage during the devolopment of lung cancer does it start to occur?

Spread of the tumor: Metasteses means the tumor cells spread from where the tumor starts to other places. Lung cancer can go to bones, the brain, liver, and other. Hard to say when/if it happens during the course of the disease.

Distant spread: A tumor is said to have metastasized when it spreads to a distant site through lymphatics or blood vessels. The molecular changes in the tumor associated with ability to metastasize vary with different tumors and are not clearly defined. In some types of lung cancers, metastases can occur even before cancer becomes detectable by x-ray.