I am looking for a database which provides information on the change in the expression of protein before and after chemotherapy. Any information in this regard would be appreciated.
I am not sure if there is an exact data base dealing with changes in proton or gene expression pre & post chemo treatment. But some help, not completely sure can probably be there on COSMIC & USGC I guess.
However, I feel I my knowledge may be partial about these website
Perhaps consult a bionfomatician on tho sealing wit cancer
GEO (https://www.ncbi.nlm.nih.gov/gds/), TCGA (https://portal.gdc.cancer.gov/) and cBioPortal (http://www.cbioportal.org/) are some of the data repository for gene expression data. But only GEO has some data related to your query. There are few datasets in GEO comparing chemotherapy samples and also as time series data.
ImmPort (http://www.immport.org/) provides shared data on clinical trials experiments and basic research data.
I have surely compared changes in protein expression during the cancer therapy using the edible Japanese Fucoidan (a true cancer drug/foodstuff) and during the therapy by the drug of D-Biotin (please see files; HepG2 fucoidan and JMBT Alopecia).
Further, recently we have reported that human breast milk is superior to bovine milk via comparing the protein expressions (please see file; The Fascio Effect).