Three cases of malignant bone tumors which took an interesting clinical course immunologically, are reported.
Case 1. A case of malignant lymphoma which had spontaneous regression.
Case 2. A case of osteosarcoma where it was considered that the malignant activity might be increased by pregnancy. (anergy induced by pregnancy).
Case 3. A case of osteosarcoma where it was considered that the malignant activity might be increased by a decrease in local resistance induced by multi-operations.
We discuss the clinical courses of these cases from an immunological view, regarding host-tumor relationship. The concept of cancer immunology is not always recognized in the clinical field, however, and there are many reports describing that radiotherapy, chemotherapy and operative therapy depress the immune response of the host. Although it may be nonspecific, immunostimulant therapy should be employed in treating malignant tumors.