I've heard from breast cancer patients who were bumped from the T-DM1 clinical trial because of disease progression, which meant that their cancer was growing despite the drug. Bumped off the trial because of disease progression? Wonder how many more patients there were like this?
Response rates (how much a tumor decreased in size) can be inflated when excluding patients during clinical trials (evaluable patients). Patients not considered "evaluable" are often those who do not get the benefit of an entire treatment plan. The response rate is calculated after removing patients, who die or have been excluded, from the calculation. This inflates the response rate.
But clinical oncologists want to publish their papers. They need to report on the outcomes of their experiments, but if they had to wait for survival data, it could take years until all the data was aggregated. That wouldn't bode well for them to participate in pharma-sponsored trials in the future.
Response rates give clinical oncologists the opportunity to take a more optimistic look at therapies that have limited success. They can describe results as being complete remission, partial remission or simply clinical improvement.
If they treat all patients for three weeks, they can fairly evaluate the efficacy of a compound, which takes that lone (on average) before it can be regarded as effective. If they disregard all patients who die or were excluded after onset of therapy, and include only those treated three weeks or more, they can improve their data.
To justify their existence, they have to publish papers. That's what they do.
http://cancerfocus.org/forum/showthread.php?t=3768
Progression-free survival (PFS) is the length of time during and after treatment in which a patient is living with a disease that does not get worse. Time to progression (TTP) is a measure of time after a disease is diagnosed (or treated) until the disease starts to get worse.
In the Annals of Oncology, it states that clinical investigators seem to be frequently using PFS and TTP interchangeably in cancer. Such use of terms may lead to confusion when results of different trials are compared.
Clinical trials virtually always have progression-free survival as a primary endpoint. Without imaging studies, one can't get accurate time to progression data. So tests are performed for the benefit of drug companies seeking new drug approval, for clinical investigators seeking contracts and publications, and for clinicians seeking an easy way to make clinical decisions.
The final arbiter of clinical approval is overall survival. Progression-free survival does not address the patient's quality of life during what little additional months of some serious side effects that can be experienced. And drug response is not even a reliable predictor of overall survival. Overall survival is based on death from any cause like side effects of treatment and effects on survival after relapse.