How soon after CAR T-cell therapy can salvage radiation be delivered?

This is another important question. In our practice, the earliest we have treated patients is after their first post-CAR-T PET/CT at day 30. An abstract presented in an oral presentation at this year's ASTRO meeting by Dr. @Dr. First Last describes that radiation to sites of incomplete response at this early post-CAR-T timepoint improves outcomes. There has been some resistance to radiation at this early timepoint, since a proportion of patients will ultimately convert from a PR at 30 days post-CAR-T to a CR at 90 days or later without needing further therapy. There is also a theoretical risk to the CAR-T cells from radiation. Methods are needed to select which patients with PR at 30 days are at the highest risk of progressing and may benef...

In our practice, we routinely obtain a day+30 PET scan to evaluate response after CAR T-cell therapy. If there is a residual disease, particularly, a limited residual disease with a Deauville score of 4-5, we offer salvage radiation therapy at this point in time.

While acknowledging that 20-30% of patients can spontaneously achieve CR by Day+90-100 PET without added therapy, we consider delaying salvage therapy until this time point. Nonetheless, our data indicates enhanced progression-free survival and overall survival with earlier intervention.

For small sites or rapidly progressive diseases, we have used radiation much more often prior to CAR T cell therapy, right after T cells have been collected (“bridging” instead of chemo). This worked out surprisingly well and these patients have had excellent disease control.