Neutropenia (low white blood cell count) on the 12th-14th day after FEC chemotherapy is not uncommon. The Filgrastim should help shorten the length of time that his white count is so low. If he tolerates this dose of chemotherapy; if he does not become infected or ill during the period of time that his white count is low, then they may not change the dose of the chemotherapy drugs. However, if the low white count does result in a fever or infection that requires antibiotics and hospitalization, they may very well decide to decrease the dose of the drugs.
Dosing of chemotherapy drugs is based on body surface area - not just weight. If his weight loss is severe enough by the time the next treatment is due, they may decide to lower the dosage to accomodate the change in body size.
The goal of cancer therapy is to try to kill as many cancer cells as quickly as possible. Certain treatment protocols allow some flexibility in number of and timing of treatments, but the overall goal is to get as effective an amount of treatment in as possible. In certain protocols, and I don't know for sure which one your husband is on, the number of treatments and amount of drug depend partly on the maximum allowable dosage of the anthracycline (epirubicin) that is safe for the heart.
You really need to discuss these questions with your oncologist and oncology nurse. Without knowing your husband's case better, and not being able to see him in the flesh, it is difficult to answer whether or not his overall well-being or lack of well-being is of a severity to require a decrease in his doses or dosage of medication. Oncology nurses are a treasure trove of information and advice, my patients often tell the oncology nurses things that they would not mention to me, yet they are still important.
I wish you and your husband well. Too often, men are overlooked by the support groups for breast cancer, and they can feel sort of "un-attended" by the larger family of breast cancer survivors. Perhaps you could see if your local cancer society or Komen Foundation could put you in touch with other men who have gone through what your husband is going through now.
Thirty years of practicing medical oncology