| Medicine is a science of statistics and nowhere is | | | | Remissions can either be complete or partial |
| this more apparent than in cancer treatment. | | | | depending on whether or not any evidence of |
| Here is a guide to understanding some of the | | | | cancer remains. Obviously, if no cancer can be |
| statistical terms you will run into when discussing | | | | found after treatment then the remission is |
| cancer treatment. | | | | complete. |
| Firstly, you need to know that no one can predict | | | | If the cancer is smaller but hasn't disappeared |
| with total certainty any patient's exact outcome. | | | | completely then the patient has experienced a |
| Instead, cancer mortality rates are based on the | | | | partial remission. |
| outcomes of large numbers of people who have | | | | A complete remission may represent a cure. But |
| had the same disease. In other words, the | | | | there is still a chance that the cancer will return |
| statistics that will be quoted to you are only | | | | depending on the type of cancer. In people who |
| probabilities. | | | | achieve only partial remissions, the cancer nearly |
| A second thing to know is that not all cancers | | | | always regrows. |
| have the same outcomes. In other words -- | | | | Are there any other statistical terms I should be |
| some cancers are deadlier than others. | | | | aware of? |
| And the third thing to realize is that the probability | | | | The 5 year survival rate tells you how many |
| of being cured depends very much on the stage | | | | people are alive at the end of 5 years but it |
| of your cancer. | | | | doesn't tell you how many of these people are in |
| For example, in all cancers, patients with stage 1 | | | | complete remission at the end of 5 years (in |
| disease have better survival rates than patients | | | | other words how many people have survived for |
| with stage 2 disease. And patients with stage 2 | | | | 5 years and have no evidence of cancer). |
| disease have better survival rates than patients | | | | So here are two more specific terms: |
| with stage 3 disease. And stage 3 patients have | | | | Disease-free 5 year survival rate. This is the |
| better survival rates than stage 4 patients. | | | | percentage of people who are not only alive after |
| That's why it's so critical for you to know what | | | | 5 years but are in complete remission. |
| stage of the disease you have. | | | | Progression-free 5 survival rate. This is the |
| What is 5 year survival? | | | | percentage of people who are alive after 5 years |
| When doctors quote the probability of survival, | | | | but who still have evidence of cancer, although |
| they don't tell you that you're supposed to live 3 | | | | the cancer isn't progressing. This includes people |
| years and 3 months. Instead, they quote you a | | | | who may have had some success with treatment |
| figure that's called the 5 year survival. This | | | | but not enough to completely eradicate their |
| number represents the probability that someone | | | | cancer. |
| with your disease will be alive at the end of 5 | | | | Two other statistical terms that you should be |
| years. | | | | aware of are relative risk and absolute risk: |
| For example, if the 5 year survival is 25%, this | | | | Absolute Risk Reduction Or Benefit. This is the |
| means that the odds of being alive after 5 years | | | | absolute difference in results between alternatives. |
| are 25%. It's important to look at the particular | | | | So, for example, if treatment A increased survival |
| group of patient for whom the 5 year survival is | | | | by 22% and treatment B increased survival by |
| being quoted. For example, it could include all | | | | 20% then treatment A resulted in an absolute |
| patients with a certain type of cancer or it could | | | | benefit of (22%-20%) = 2%. |
| only include patients with a certain stage of that | | | | Relative Risk Reduction Or Benefit. This is the |
| cancer. | | | | relative difference in results between alternatives. |
| For example, 49 percent, or about half, of people | | | | So, in the above example, the relative benefit is |
| diagnosed with early-stage lung cancer live for at | | | | (22%-20%)/20% = 10%. This number is |
| least five years after diagnosis. So, the five year | | | | calculated by taking the difference in outcome as |
| survival for early-stage lung cancer is 49%. | | | | a percentage. |
| Contrast this with the five year survival rate for | | | | You should beware that often results are |
| people diagnosed with lung cancer that has spread | | | | presented as relative risk reduction or benefit |
| (metastasized) to other areas of the body which | | | | because the numbers sound more impressive. For |
| is only 3 percent. | | | | example, in the above example, a relative benefit |
| So, as you can see, you want to find out what | | | | of 10% sounds more impressive than an absolute |
| the survival rate is for patients with the same | | | | benefit of 2%. |
| stage of disease. | | | | Hopefully, now you'll be able to be a little more |
| What is remission? | | | | discerning about cancer statistics. |
| Remission refers to a shrinking of a cancer. | | | | |