Biden's prostate cancer diagnosis raises questions about screening and how the disease spreads

Former President Joe Biden's diagnosis with an advanced stage of prostate cancer that has metastasized, or spread, to his bones prompted an outpouring of concern and questions about his condition. Those questions include how long the cancer may have taken to develop and whether he was screened for it during earlier checkups. 

While it's unclear exactly how long Biden has had cancer, its rapid spread is attributed to it being an aggressive form of the disease. His cancer was categorized as having a Gleason score of 9, which places him in Grade Group 5, the most severe category. The Gleason score is a system for grading the severity of prostate cancer based on analysis of cell samples under a microscope.

When prostate cancer is more advanced and spreads, the bones are among the areas most likely to be affected. It can also commonly spread to the lymph nodes, liver or lungs, according to the Mayo Clinic.