You can. Generally doctors recommend waiting five half-lives before restarting breastfeeding, which, given the long half-lives that many chemotherapy drugs have, may not be easy. A half-life is the length of time it takes for a drug to be eliminated from the body. Thus, a drug with a half-life of one hour (very short) would be 98 percent eliminated from the body in five hours. Doxorubicin (Adriamycin) has a half-life of 24 to 36 hours, so to be safe, you would have to wait at least five days, maybe one week, before resuming breastfeeding. But even a half-life of 24 to 36 hours is relatively short for chemotherapy drugs.
There is also a theoretical concern regarding milk production: In order to maintain your chances of resuming breastfeeding, it's helpful to express your milk while being treated, but chemotherapy drugs attack cells with high growth rates, like lactocytes (milk-producing cells), and thus may damage these cells with unknown long-term consequences. This is theoretical only and not proved, but it is a possibility you should prepare yourself for.