Interpreting NA Values in 19Q4 PRISM Primary screen


I have downloaded the 19Q4 PRISM primary screen collapsed logfold change file. I am noticing that for some cell lines majority of the drug values are NA, is it right to assume that NA values are because they have been filtered out for some reason? When focusing on just breast cancer cell lines, it seems like majority of the cell lines have NA values across most of the drugs. Is the correct interpretation that these breast cancer cell lines did not respond well or are not suitable for drug treatments?