Chemo: Dogs Vs. Humans

Chemo for dogs is not typically to cure, rather, it is used to extend your dog's life by putting the cancer into remission for a period of time. There are two reasons for this -

Dog chemotherapy drugs (although they are technically human-grade) are not given at their maximum dosage. Most owners would not be willing to give their dogs such a high dosage as it would inflict the terrible side effects we associate with chemotherapy: nausea, vomiting, hair loss, etc. and as owners, we are responsible for their quality of life, we cannot ask what they want. Humans can decide for themselves if they willing to deal with the side effects.

The trade off of minimal side effects is the cancer becomes resistant to the chemotherapy. The cancer cell is able to code it's genes to make "protein pumps" on the cell surface, which pump the drugs out of cell. The pumps are known as MDR (multiple drug resistance) This is also the survival mechanism of a normal cell, the cancer is pumping the poison (in this case chemo) out to detoxify.

(This is why the use of multiple chemo drugs, like CHOP, are the best weapon for cancer in dogs.)