This article discusses the concept of 5-year survival in cancer, and addresses some common misinterpretations.
Early on in my career, I was counseling Mrs T, a woman with stage I breast cancer. I explained the diagnosis and its implications, laid out the plan of treatment and then told her the prognosis – “You have a 98 per cent chance of 5-year survival.” Expecting her to be pleased with this prognosis, I was surprised when she broke down sobbing.
“So, doctor, I have only 5 years to live?”
“No, Mrs T. It simply means that at the end of 5 years, 98 out of 100 women of your age who have your type and stage of cancer will be alive.”
“So what happens after 5 years? Is there no hope that I will live longer?”
“No, its not like that at all. Beyond 5 years, the number of recurrences as well as deaths become very less. In other words, if you are well at the end of 5 years, the chances are extremely high that you will continue to be healthy and have a normal lifespan.”
“So if I am OK at 5 years, does it mean that I am cured of cancer?”
“Unfortunately, we cannot guarantee that. Cancer can come back even after 5 years. However, for most cancers, recurrence beyond 5 years is a rare occurrence.”
Over the years, I have refined my counseling, and at the end of the discussion, always make sure that my patient and their family understand this concept of 5-year survival.
Some other common questions I get are:
“How did you get this number of 98 percent?”
“This survival rate is based on statistics on women at your age, with this specific type and stage of cancer. It is like saying the life expectancy in India is 70 years. We cannot accurately predict the outcome for any individual patient, just like we cannot say that every person in India will live for exactly 70 years.
“Why do you oncologists talk about 5-year survival? Why not 2-year survival, or 10 year survival?”
5-year survival rate is a conventional benchmark in oncology. It has been widely accepted as a standard measure because it provides a reasonable time-frame to evaluate the effectiveness of cancer treatments while also being practical to measure and report.
A 5-year survival rate provides a balance between the need for long-term survival data and the practical limitations of collecting and analyzing data over a more extended period.
Suppose we want to compare a promising new treatment with an established standard treatment, measuring a difference in 5-year survival can be very useful
However, other time-frames such as 2-year or 10-year survival rates are also sometimes used, depending on the specific type of cancer and the purpose of the analysis. For example, for cancers with a relatively short survival time, such as pancreatic cancer, a 2-year survival rate may be more appropriate. On the other hand, for slow-growing cancers, such as prostate cancer, a 10-year survival rate may be more relevant.