Calcium-47 and strontium-85 tracer studies as a guide to isotope therapy of bone metastases.

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Palliative therapy for patients with metastases from mammary cancer constitutes an important problem. It has been well demonstrated that endocrine ablative therapy yields effective systemic control and that irradiation affords useful local control of the disease in a significant number of patients. Appropriate integration of these two modalities can frequently produce worthwhile palliation. Friedell and Storaasli (1) were the first to report the use of P32 intravenously for the treatment of widespread osseous mammary metastases. In a more recent evaluation, Storaasli et al. (2) reported objective improvement in 26 per cent of a selected group of patients with predominantly osseous metastases receiving intravenous injections of P32. These workers have also combined adrenalectomy and intravenous P32 in a small, highly selected series of cases. Fifteen of 22 patients obtained objective improvement averaging 15+ months in duration. Although these results suggest that there is an additive effect of these two therapeutic agents, this could not be conclusively demonstrated. The rationale for isotope therapy is based on selective uptake of the isotope in the area of the lesion. The uptake of P32 in human mammary cancer does not appear to be very selective. Kenney et al. (3) found a differential uptake in primary breast cancers of 2 to 7 times that of normal breast tissue, and lymph nodes which contained metastatic foci of breast cancer took up to 1.3 to 2.8 times as much of the isotope as uninvolved lymph nodes. Therapeutic trials with intravenous P32 (1, 2, 4) have produced improvement only in metastatic osseous lesions, whereas soft-tissue lesions are unaffected. On the other hand, a more selective uptake of P32 has been demonstrated in osseous mammary metastases both by direct measurement (5) and by radioautographs (1, 4). These observations indicate that selective uptake of P32 in bone surrounding the tumor affords the major potential for the therapeutic use of isotopes. The use of P32 for the treatment of bone metastases has so far been purely empirical, since no convenient method exists for the measurement of differential uptake of P32 in individual patients. Since only one-fourth of a selected group obtained benefit from this therapy, it would seem important to be able to select those who are likely to be helped, as well as to avoid the hazards of this procedure in those who will probably not be benefited. The recent availability of a radioactive isotope of calcium (Ca47) has provided an ideal tracer for calcium kinetic studies and for local uptake measurements over the skeleton by external counting. Preliminary results of Ca47 tracer studies in patients with malignant lesions of bone have shown that both progressive and healing bone lesions may be associated with an increased accretion rate of calcium in the skeleton as a whole due to an increased local uptake in the lesion areas (6).