Is survival really better after repeated lung metastasectomy?

Several groups have observed that average survival time after a second lung metastasectomy is longer than after a first metastasectomy. The randomised controlled trial Pulmonary Metastasectomy in Colorectal Cancer (PulMiCC) found no survival benefit from lung metastasectomy. In fact, median survival was longer, and four-year overall survival was higher, in the control group than in those randomly assigned to metastasectomy, although not significantly so. The illusion of benefit is because survival without metastasectomy has been assumed to be near zero, as stated in Society of Thoracic Surgeons' Expert Consensus Document on Pulmonary Metastasectomy 2019. It has been repeatedly found that survival is influenced by the selection of patients who have characteristics associated with better prognosis. The passage of time while monitoring and assessing patients, and observing their rate of progression, provides for immortal time bias. Reselection of the most favourable patients for repeated metastasectomy is the likely reason for any differences in survival between first and repeated metastasectomy operations.