They found a correlation between a protein (ENPP1) and breast cancer metastasis that they feel is a very strong signaler for pembrolizumab immunotherapy resistance. This would be helpful information to help get to the right dosage of medicine faster (or skip a class of drugs entirely), which might save weeks or months of taking a drug that effectively is neutralized by the resistance.
Additionally, hopefully new medicine will (after more research) go after this protein and see if attacking it allows the immune system to better resist cancer itself.
It's also worth noting that two of the researchers involved in this work own a company to try to utilize patents around this work.