Splitter.

Also in the plenary session yesterday was reporting of outcomes in ACNS0331 per molecular subgroup. Those on a peds rotation within the last decade may recall that this trial was designed to assess in standard risk medulloblastoma (1) if craniospinal irradiation (CSI) dose can safely be reduced from the standard 23.4 Gy to 18 Gy for patients <8 years old and (2) if the boost field can be reduced from the entire posterior fossa to just the tumor bed for patients <22 years old. At first glance, reducing CSI dose had a detrimental effect on event-free survival (EFS) while reducing the boost field did not. However, remembering medulloblastoma can be molecularly-divided into at least four distinct diseases (i.e., WNT, SHH, groups 3, group 4), the outcomes should be split accordingly. For instance, those with SHH disease actually had significantly higher EFS with reduced field boost, while those with group 4 disease did dramatically worse with reduced-dose CSI—both heavily influencing the overall rates. TBL: Here’s to hoping oral board examiners are satisfied with the blanket statement “molecular subgroups and further genetic profiling within those subgroups inform who can safely receive de-intensified radiation doses and volumes for standard-risk medulloblastoma.” | Michalski, ASTRO 2020