The use of active specific
immunotherapy (ASI) for
cancer (
cancer "vaccines") is still in its scientific infancy despite several decades of clinical and basic research. What has been established is the principle that stimulation of the immune response by "crude" (i.e., whole cell-derived)
vaccines has led, in a proportion of patients, to rejection of
tumor masses, in some instances for 10 years or more. Scientific investigations into the nature of recognition of
tumor antigenic determinants (
epitopes) by cytolytic T cells have begun to elucidate the mechanisms underlying rejection, making more precise
vaccines possible. Yet there should be caution about assuming that a single
epitope or even a few
epitopes combined will be as effective as the "crude" materials, which might better be thought of as "polyvalent." ASI in at least one instance may have cured
melanoma in a patient with metastatic disease, but that patient developed another immunologically and genetically distinct
melanoma. This may provide an example of both immunological surveillance against the emergence of new
melanomas and immunological selection of an immunologically resistant
tumor. Combinations of
vaccines with
cytokines, cytolytic T cell infusions, or
chemotherapy may improve the response rates and durations of survival achievable with
vaccines alone. The best rationale for synthetically derived
vaccines may be for prophylaxis-that is, as a true
vaccine-where the use of
tumor-derived materials in normal individuals is difficult to justify ethically.