ALK and cancer: Progression-free survival may be considered as a surrogate marker for overall survival, but it has not been validated as such.[53] Overall survival is the most objective outcome with which to assess efficacy of cancer treatments; however, its measurement is confounded by the changing of treatments after disease progression.[53] Most RCTs allowed participants receiving chemotherapy to switch to an ALK inhibitor after disease progression, and we were unable to analyze the data separately for those who did or did not switch treatments.