Simply put, the grade is what your cancer looks like under the microscope. This can only be determined by a biopsy–which allows the pathologist to assign a grade based upon the microscopic appearance of the sample. The less the cancerous cells look like normal cells (another term for very abnormal cells is poorly differentiated), the higher the grade. Basically, the grade suggests how the cancer will behave. Higher grade cancers are more aggressive and more likely to spread over time as well as more likely to be fatal.

For prostate cancer, the grade is also called the Gleason score, which describes the shape of the malignant glands under the microscope (AKA the patterns). Dr. Donald Gleason was a famous pathologist from Minnesota who derived the Gleason scoring system in the 1960s. It was revised in 1974 and again in 2005. The Gleason patterns are 3 (well-differentiated, much less aggressive), 4 (intermediate aggressiveness), and 5 (poorly differentiated and very aggressive). To come up with a Gleason score, the two most prevalent patterns in the biopsy section are added together in order of prevalence. Gleason scores go from 6 to 10. For instance, a biopsy sample that is mostly pattern 3 with some pattern 4 is called Gleason 3 + 4 = 7. Conversely, if it is comprised of the same patterns, but most is pattern 4, it is called Gleason 4 + 3 = 7. These two forms of Gleason 7 cancer have slightly different prognoses. As you can imagine, Gleason 3 + 3 = 6 cancers are not very aggressive. In fact, Gleason 6 cancer rarely causes significant problems. Gleason 10 cancers are very aggressive, but fortunately very uncommon.

The stage describes the current state of the cancer, such as how large the tumor is and whether or not it has spread outside the prostate. Essentially, the stage describes how “advanced” the cancer is. This cannot be determined by biopsy, but is instead determined by physical exam and imaging studies such as bone scan, CT scan, MRI, or PET scan. Prostate cancer typically causes no symptoms until it is at a high stage, at which time it is often incurable. Finding cancer at earlier stages is therefore very important, which is why we screen for cancers in men with no symptoms.

Putting all of this together, one can the understand that the patients who are most likely to have their lives saved by prostate cancer screening are those with low stage (caught early), and high-grade cancer (which may have quickly spread and become incurable).