Relationship of tumor immunogenicity to concentration of the oncogen

Tumors were induced sc in (BALB/c x DBA/2)F1 female mice by various concentrations of 3-methylcholanthrene (MCA) in paraffin pellets. There was an inverse relationship between MCA concentration and tumor latency (interval between MCA implantation and detection of gross tumor). The tumors were transplanted into syngeneic recipients, and material from this first transplant generation was used to immunize a series of syngeneic mice; any resulting growth was excised. Nonimmunized mice were controls. Immunized and control mice were irradiated and given an sc inoculation of a near-threshold number of tumor cells. Tumor growth from that inoculation was measured weekly in both groups and the antigenicity ratio (mean tumor size in controls/mean tumor size in immunized mice) was calculated. In a series of tumors with similar latencies, the only ones with high antigenicity ratios were those resulting from the high MCA concentration. The results suggested that tumors induced by low levels of oncogen may be good models of spontaneous neoplasia, strengthened the hypothesis that "spontaneous' tumors may actually result from low levels of oncogen, and indicated that neoplastic transformation and the development of immunogenicity are, at least in chemically induced tumors, independent changes that may be produced in the same cell when the concentration of oncogen is sufficient.