Antigenic differences between primary methylcholanthrene-induced rat sarcomas and post-surgical recurrences.

The immunogenicities of in vivo lines established from primary MCA-induced rat sarcomas have been compared with those of lines initiated from tumour recurrences at the site of the primaries' surgical excisions. Lines from two of four primary sarcomas showed little or no immunogenicity, as assessed by protection against challenge afforded by graft excision or implantation of irradiated tissue. In contrast, lines from all four recurrences were immunogenic, giving protection against up to 5 X 10(6) tumour cells. Most importantly, with all four tumours, lines established from recurrences were antigenically distinct from lines derived from their original primary sarcomas, so that immunization with regrowth lines gave no protection against the lines from the primaries, and vice versa. These studies demonstrate that primary MCA-induced sarcomas are antigenically distinct from recurrent tumors arising after surgical removal of the primaries, implying that these tumours arose by clonal amplification of separate populations of transformed cells. This may reflect proliferation of dormant neoplastic cells or the further induction of transformed cells by residual carcinogen. These findings are relevant to the multifocal origin of tumours and for the design of active immunotherapy for the treatment of recurrences or metastatic deposits.