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The fate of methylcholanthrene tumor cells in bone: analysis of immune factors in host resistance.

SPONTANEOUS REGRESSION has been reported for a variety of neoplasms. In the 130 cases documented by Everson, neuroblastoma and renal cell carcinoma were the most common cancers to demonstrate spontaneous regression [ 11. This phenomenon seldom involves skeletal metastases from these neoplasms [2] suggesting that bone may be a relatively privileged site where metastatic cells are protected from immunologic surveillance. Current evidence suggests immunity against malignancy is predominantly a cellular mechanism involving tumor cell destruction by immune lymphocytes [3]. Lysis of tumor cells requires close lymphocyte approximation as well as a high lymphocyte-tumor target cell ratio [4, 51. We wondered if anatomical and structural factors in bone protected metastatic cells from immunologic attack by preventing optimal lymphocyte-tumor cell interaction, In this work, a highly immunogenic methylcholanthrene (MCA) induced fibrosarcoma was used to immunize C57/BL female mice. Once resistance against this tumor was established the animals were rechallenged by tumor isografts injected directly into bone to determine if bone was