[Why complete or partial response can not be achieved by immunotherapy]

It has been shown that shrinkage of tumor mass can hardly be achieved by immunotherapy. However, this does not appear to indicate that the immunotherapy is ineffective in cancer treatment. Although chemotherapy can reduce a tumor mass by means of fractional kill of tumor cells and, thereby assure complete and partial responses, the cytocidal action of immunotherapy seems to be effected through constant number cell kill. When residual tumor cells in patients who underwent radical surgery are considered from a microscopic standpoint, it is suggested from the disease-free survival curve that the tumor burden is surely reduced logarithmically even in each class of patients who failed to respond to adjuvant chemotherapy. Moreover, there is a great possibility that these residual tumor cells will acquire a drug resistance. Therefore, even if the degree of cell kill potential of immunotherapy is so low that complete or partial response cannot be achieved, the role of immunotherapy in combined modality for cancer treatment is inevitably important.