One of the fruitful collaborations between IO and surgery is in the field of liver transplantation for hepatocellular carcinoma. In many western countries, waiting lists for transplantation are long due to regulatory constraints and organ shortage. Therefore, patients bearing hepatocellular carcinoma waiting for a liver transplantation are at risk of drop-out due to tumour progression. Treatment decisions for hepatocellular carcinoma on the waiting list are balanced between site conditions such as mean waiting time, surveillance program, and tumour status (T status, serum alpha-feto protein level, tumour progression rate). The severity of the liver disease is less a concern in this population, since a sudden deterioration of liver function after any interventional treatment will modify the MELD score and prompt the realization of the transplantation.
The ideal treatment should have a very good tumour control rate, and should not need to be repeated.
Indications for treatment are still debated in the literature for T1a tumours.  The drop-out rate at 6 months in a large series of 94 patients bearing T1a hepatocellular carcinomas treated either by radiofrequency ablation, chemo-embolization or percutaneous ethanol injection is low; around 5%.  In another longitudinal follow-up of 114 patients with T1A tumours who were not treated the drop-out at 2.4 years from all causes is 30%, but 88% of patients progressed to T2 stage.  Despite the lack of level one evidence supporting the IO treatment in this population, your decision should be based on common sense. In our transplantation center, where the median waiting time is 18 months, we tend to treat T1a patients with percutaneous ablation. Whether patients properly treated with thermal ablation for T1a should stay on the waiting list is a matter of concern due to the shortage of donor organs. The recent study from Reto Bale showing a 97.8% complete response rate on ablated tumours in transplanted patients  also pushes the argument toward an temporary exclusion of these patients from the waiting list.
Bridging of patients with T2 tumours on the waiting list has been more extensively analyzed in large studies. A recent meta-analysis showed that most of them limited the drop-out to less than 20% at one year.  This is a commonly adopted strategy.
Downstaging to transplant criteria is a completely different approach. The aim is to downstage but also to maintain this downstaging for a certain amount of time in order to avoid drop-out. The choice between chemoembolization and Y-90 radioembolization is currently based on the randomized study published by Salem et al.  They demonstrated that despite identical downstaging capacity and overall survival, radioembolization offers a significantly longer progression free survival.
A multidisciplinary strategy is mandatory for these patients according to the characteristics of your transplantation center.