The most reliable method of detecting bone metastases in a prostate cancer patient is a conventional bone scan. However, even in a patient with prostate cancer, not all areas of enhanced uptake on bone scan are associated with metastatic disease, particularly in the case of solitary lesions or uptake in joints. Confirmation of metastases by additional imaging modalities such as plain radiographs or MRI scans may be needed prior to making a clear diagnosis. Bone metastases may or may not be associated with painful symptoms when initially detected.1
Conventional bone scan (99mTc-MDP) versus 153Sm-EDTMP demonstrating identical uptake. 153Sm-EDTMP emits an imageable 103 keV gamma photon that can be viewed up to 3-5 days after the initial injection by either planar or single photon emission computed tomography (SPECT). Uptake and distribution of 153Sm-EDTMP are similar to those of 99mTc-MDP used in bone scans. Comparison of the two images produced by gamma radiation emitted by gamma radiation emitted from 153Sm-EDTMP and 99mTc-MDP in the same patient illustrates how similar the radiographs produced by 153Sm-EDTMP are. Thus, 153Sm-EDTMP may also be used for diagnostic imaging. Images courtesy of Todd Hoover.
In patients initially diagnosed with bone metastases and then subsequently treated with hormonal therapy, Newling and colleagues have determined that increases in serumPSA occur approximately six months prior to changes in bone scan which in turn occur approximately four months prior to patient reports of pain.2 The timing of this sequence of events in patients treated with hormonal therapy before the onset of bone metastases (most patients today) has not been well studied, but the interval between PSA rise and the onset of a positive bone scan is suspected to be much longer (more than two years on average).
Even in patients with a positive bone scan who report painful symptoms, a comprehensive examination may be needed to establish the cause of the pain and evaluate any possible complicating factors such as spinal cord compression, neuropathic conditions, and pathologic fractures. Patients with bone metastases may also have non-malignant sources of bone pain, and the causes of such pain need to be evaluated on a case by case basis. It is not uncommon for arthritis or other benign problems to cause pain in a patient with cancer.
Decay properties such as half-life and particle energy play significant roles in such important clinical characteristics of these agents as onset and duration of palliative effects and degree of and time to recovery from bone marrow suppression. The particle emission energies of 32P and 89Sr and the corresponding ranges in bone and soft tissue are much greater than those of 153Sm. Higher energy particles are associated with greater marrow toxicity as the result of the larger volumes of marrow exposed to radiation. The shorter physical half-life of 153Sm (1.9 days) results in a more rapid delivery of radiation than either 32P (14.3 days) or 89Sr (50.5 days). For example, delivery of 90% of the total dose of radiation requires approximately 3.5 half-lives of decay, a time interval of approximately one week for 153Sm, seven weeks for 32P, and 25 weeks for 89Sr.
1.Gandhok N and Sartor O.Bone-targeted therapy for prostate cancer. In: Klein EA, ed. Current clinical urology: Management of prostate cancer, second edition. Totowa: Humana Press, 2004:589-606.
2. Newling DW,Denis L,Vermeylen K.Orchiectomy versus goserelin and flutamide in the treatment of newly diagnosed metastatic prostate cancer. Analysis of the criteria of evaluation used in the European Organization for Research and Treatment of Cancer- Genitourinary Group Study 30853. Cancer 1993;72(12 suppl): 3793-3798.
3. Serafini AN, Houston SJ, Resche I, et al, Palliation of pain associated with metastatic bone cancer using samarium-153 lexidronam: A double-blind placebo-controlled study. J Clin Oncol 1998;16:1574-1581.
4. Sartor O, Reid RH, Hoskin PJ, et al, Samarium-153-lexidronam complex for the treatment of painful bone metastases in hormone refractory prostate cancer.Urology 2004;63:940-945.
5. Tu SM,Millikan RE,Mengistu B, et al.Bone-targeted therapy for advanced androgen-independent carcinoma of the prostate: a randomised phase II trial. Lancet. 2001; 357(9253):336-41.
6. Widmark A, Linne T, Modig H, Johansson L. Optimizing the time of co-administration of docetaxel and samarium-153 for advanced androgen independent carcinoma of the prostate [abstract]. Proc Am Soc Clin Oncol 2003;22:433.
7. Arnsmeier SL, Spies S, Shervin D, et al. Phase I/II study of taxane and estramustine with samarium in patients with hormone refractory prostate cancer [abstract]. Proc Am Soc Clin Oncol 2004;23:438.
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