Before revision:  Since validating drug combinations via direct screening is prohibitively expensive due to combinatorial explosion, recent approaches have applied machine learning to identify synergistic combinations for cancer . However, these approaches is not readily applicable to many diseases with limited combination data.
After revision:  Since validating drug combinations via direct screening is prohibitively expensive due to combinatorial explosion, recent approaches have applied machine learning to identify synergistic combinations for cancer , but they are not applicable to new diseases with limited combination data.