Although chemotherapy can still be effective if started later after surgery the possibility of it being less effective is increased over time for two reasons. Every time cancers cells divide the chance that a family of cells with changes that give them a natural resistance to chemotherapy drugs arises increases. Secondly chemotherapy is given after surgery to eliminate any microscopic disease that may be left and will eventually grow. The longer the chemotherapy is delayed the cancer cells can increase. Having said that, chemotherapy can’t be started too early after surgery or healing of the wound may slowed.