Most, or perhaps, all neoplasms contain surface antigens which are not recognized as “self” by the immunologic mechanisms of the animals in which the neoplasms originate. Almost all of the putatively nonviral tumors are individually specific and few, if any, cross-reactions occur among them. The antigenic titer varies greatly and is related to the latent period and the immunologic reactivity of the tumor host. This relationship is almost certainly due to immunoselection. The antigens are found in early premalignant lesions and the immune mechanism suppresses many of these before they reach macroscopic size and before they undergo progression to malignancy. It is hypothesized that the tumor antigens represent an alteration in a normal cell-surface regulatory site or sites. Whether they are encoded but repressed in the genome of the normal cell or are the result of mutation has not been determined.

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Supported by USPHS Grants CA-08856, CA-06927, and FR-05539 and an Appropriation from the Commonwealth of Pennsylvania.

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