1. Aetna considers the radiopharmaceuticals strontium-89 (Metastron®) and samarium-153 (Quadramet) medically necessary for treatment of bone pain in cancer members with painful skeletal metastases (e.g., bone metastases from breast cancer, liver cancer, prostate cancer, or any other cancer that metastasizes to the bone).

2. Aetna considers radiopharmaceuticals such as strontium-89 (Metastron®) and samarium-153 (Quadramet) experimental and investigational for all other indications including use in members with cancer not involving the bone, and intra-articular injection of samarium-153 particulate hydroxyapatite for the treatment of knee synovitis in members with rheumatoid arthritis.

Strontium-89 is an effective alternative for the treatment of bone pain in patients with painful skeletal metastases.  The drug is only a palliative measure and not a cure for bone pain or cancer.  Moreover, it is ineffective in relieving pain originating from soft tissue tumors, unless bone metastases are involved.

Strontium-89 was approved by the Food and Drug Administration (FDA) for the treatment of bone pain in cancer patients with painful skeletal metastases.  It is not indicated for use in patients with cancer not involving the bone.  Strontium-89 is marketed under the brand name Metastron through a joint venture of Amersham Healthcare and Zeneca Pharmaceuticals.

Strontium-89 is a beta-emitting radionuclide that preferably localizes in areas of active bone formation (areas of high osteoblast activity such as metastatic lesions).  It functions as a calcium analog that releases high-energy beta particles as the compound decays to yttruim-89.  This local radiation results in at least partial pain relief without extensive hematologic toxicity or myelosuppression.  The mechanism by which strontium-89 relieves bone pain is not known.  Some believe that local irradiation stops the tumor from producing pain-producing enzymes, while others believe it may act through suppression of tumor growth.

Strontium-89 is indicated for patients with definite signs of discomfort from skeletal metastases and with inadequate relief with other forms of therapy (e.g., chemotherapy, hormone therapy, and analgesics).  Other causes of bone pain (e.g., osteoarthritis, nerve root compression) should be ruled out.  Strontium-89 is contraindicated in patients with elevated calcium levels.  According to established guidelines, white blood counts should be greater than 2,400 to 3,000 and platelets greater than 40 to 100 10(9)/L prior to therapy.  Product information indicates that caution should be used in patients with platelet counts below 60 x 10(9)/L and white blood cell counts below 2,400.

Evidence of pain relief is generally seen within 7 to 21 days and sustained for 3 to 6 months.  The literature indicates that a repeat dose can be administered at 3-month intervals if necessary.

Amato et al (2008) noted that bone-targeted therapy that combines strontium-89 (Sr-89) with alternating weekly chemohormonal therapy may improve clinical outcomes in patients with metastatic hormone-refractory prostate cancer.  This phase II study examined the addition of Sr-89 to an alternating weekly regimen of doxorubicin and ketoconazole with paclitaxel and estramustine in patients with progressive prostate cancer and bone involvement.  A total of 29 patients with progressive adenocarcinoma of the prostate and osteoblastic bone metastases who failed conventional hormonal therapy were registered for the study.  Of those, 27 were treated with Sr-89 on day 1 of week 1.  On weeks 1, 3, and 5, patients received doxorubicin (20 mg/m on day 1) and oral ketoconazole (400 mg 3 times a day for 7 days).  On weeks 2, 4, and 6, patients received paclitaxel (100 mg/m(2)) and oral estramustine (280 mg 3 times a day for 7 days).  No treatment was given during weeks 7 and 8.  Cycles were repeated every 8 weeks.  A greater than or equal to 50 % reduction in prostate-specific antigen level was maintained for at least 8 weeks in 77.7 % of the patients (n = 21) at 16 weeks and in 66.6 % (n = 18) at 32 weeks.  The median progression-free survival was 11.27 months (range of 1.83 to 29.53), and the median overall survival was 22.67 months (range of 1.83 to 57.73+).  Two patients died during study because of disease progression.  Overall, the chemotherapy combined with Sr-89 was well-tolerated.  The authors concluded that these findings demonstrated that the combination of alternating weekly chemohormonal therapies with Sr-89 resulted in a prolonged progression-free and overall survival with acceptable toxicity.  They stated that further investigation of combination therapies with Sr-89 is warranted.

Tu and Lin (2008) stated that the propensity of prostate cancer to metastasize to bone and the prognostic significance of bone metastasis suggest that effective treatment of bone metastasis may provide clinical benefits.  Both osteoblasts and osteoclasts have been shown to play a central role in the interactions between the metastatic prostate cancer cells and bone.  Although most prostate cancer bone metastasis is osteoblastic, it remains unclear which cell type is initially involved in the process.  Other components in the bone, such as the endothelium and stroma, may also play an important role in this process.  The osteoblastic feature of prostate cancer bone metastasis has led to therapies focused on targeting osteoblast activity.  Clinical trials targeting osteoblasts use radiopharmaceuticals (e.g., Sr-89 and samarium-153), the endothelin A receptor inhibitor atrasentan, or the vitamin D analog calcitriol.

Quadramet (samarium-153 lexidronam injection) has been approved to treat patients with severe pain associated with cancers that have spread to bone.  It is indicated for relief of pain in patients with confirmed osteoblastic metastatic bone lesions that enhance on radionuclide bone scan.  In a review on the role of radiopharmaceuticals in the palliation of metastatic bone pain in adults with uncomplicated, multi-focal painful bone metastases whose pain is not controlled with conventional analgesic regimens, Bauman et al (2005) concluded that use of single-agent radiopharmaceuticals (e.g., strontium-89 and samarium-153) should be considered as a possible option for the palliation of multiple sites of bone pain from metastatic cancer where pain control with conventional analgesic regimens is unsatisfactory and where activity on a bone scan of the painful lesions is demonstrated.  This is in agreement with the observation of Silberstein (2005) as well as that of Finlay et al (2005).

In a randomized, controlled, double-blind study, dos Santos et al (2009) examined the effectiveness of radiation synovectomy with samarium-153 particulate hydroxyapatite in rheumatoid arthritis patients with knee synovitis.  A total of 58 patients (60 knees) with chronic knee synovitis were randomized to receive either an intra-articular injection with 40 mg triamcinolone hexacetonide alone (TH group) or 40 mg triamcinolone hexacetonide combined with 15 mCi samarium-153 particulate hydroxyapatite (Sm/TH group).  Blinded examination at baseline (T0) and at 1 (T1), 4 (T4), 12 (T12), 32 (T32), and 48 (T48) weeks post-intervention were performed on all patients and included a visual analog scale for joint pain and swelling as well as data on morning stiffness, flexion, extension, knee circumference, Likert scale of improvement, percentage of improvement, SF-36 generic quality of life questionnaire, Stanford Health Assessment Questionnaire (HAQ), Lequesne index, use of non-steroidal anti-inflammatory drugs or oral corticosteroids, events and adverse effects, calls to the physician, and hospital visits.  The sample was homogeneous at baseline, and there were no withdrawals.  Improvement was observed in both groups in relation to T0, but no statistically significant differences between groups were observed regarding all variables at the time points studied.  The Sm/TH group exhibited more adverse effects at T1 (p < 0.05), but these were mild and transitory.  No severe adverse effects were reported during follow-up.  The authors concluded that intra-articular injection of samarium-153 particulate hydroxyapatite (15 mCi) with 40 mg of triamcinolone hexacetonide is not superior to triamcinolone hexacetonide alone for the treatment of knee synovitis in patients with rheumatoid arthritis at 1 year of follow-up.

In a phase I clinical trial, Valicenti and colleagues (2011) determined the maximum tolerated dose of samarium-153 EDTMP (153Sm) with hormonal therapy (HT) and radiation therapy (RT) in high-risk clinically non-metastatic prostate cancer.  High-risk M0 prostate cancer patients (prostate-specific antigen [PSA] greater than 20 ng/ml, Gleason score greater than 7, or greater than T3) were eligible for this prospective trial of dose-escalated radioactive 153Sm-EDTMP (0.25 to 2.0 mCi/kg body weight) as primary or post-operative therapy.  After 1 month of HT, 153Sm-EDTMP was administered followed by 4 more months of HT, 46.8 Gy to the pelvic region and 23.4 Gy to the prostate target (TD = 70.2 Gy).  The primary end point was grade III toxicity or higher by the National Cancer Institute Common Toxicity Criteria.  A total of 29 patients were enrolled in this study (median PSA = 8.2 ng/ml, 27/29 (93 %) T stage greater than or equal to T2b, 24/29 (83 %) had Gleason greaterthan 7) and received 153Sm-EDTMP (0.25 mCi/kg, 4 patients; 0.5 mCi/kg, 4 patients; 0.75 mCi/kg, 6 patients; 1.0 mCi/kg, 6 patients; 1.5 mCi/kg, 5 patients; 2.0 mCi/kg, 4 patients).  Twenty-eight patients underwent all planned therapy without delays (1 patient required surgery before the start of RT).  With a median follow-up time of 23 months, there were 2 patients (7 %) experiencing grade III hematologic toxicity.  There were no other grade III or IV side effects.  The authors concluded that these findings demonstrated that 2 mCi/kg 153Sm -EDTMP with HT and RT was safe and feasible in men with high-risk M0 prostate cancer.  They noted that a phase II study to test this treatment is currently underway by the Radiation Therapy Oncology Group.

Berger and colleagues (2011) noted that bone metastatic patients with osteosarcoma have a very poor prognosis.  Targeted radiation therapy has been pursued as a valid alternative.  The primary end point of this study was progression-free survival (PFS) at 4 months.  A total of 22 osteosarcoma patients were treated with samarium-153 EDTMP ((153)Sm-EDTMP) at various dosages.  Administered activities ranged from 150 (3 mCi/kg) to 1,140 MBq/kg (30 mCi/kg).  Autologous hematopoietic stem cell infusion was carried out on day 14 after the (153)Sm-EDTMP infusion.  The median PFS was 61 days (18 to 436 days) and the median overall survival (OS) was 189 days (31 to 1175 days).  PFS and OS for the entire patient population were 32 % [95 % confidence interval (CI): 16 to 50] and 76 % (95 % CI: 52 to 89) at 4 months, respectively.  No statistical differences emerged according to (153)Sm-EDTMP administered or 24-hr retained activity.  One-month pain palliation was only observed in a minority of subjects and in none at 4 months.  The authors concluded that based on their findings, the PFS is dramatically short even when higher activity of (153)Sm-EDTMP is administered.  They stated that this would mean that, even at high level, (153)Sm-EDTMP is itself ineffective against relapsed osteosarcoma or the residual activity is too low to be active on these particular subsets of patients.

Note: Individuals with disseminated intravascular coagulation must be excluded from therapy with strontium-89 and samarium-153 therapy. The American College of Radiology (ACR) and the American Society for Radiation Oncology (ASTRO)'s practice guideline for the performance of therapy with unsealed radiopharmaceutical sources (2010) listed disseminated intravascular coagulation (DIC) as a contraindication of strontium-89 and samarium-153.  Thus, patients with DIC must be excluded from therapy with strontium-89 and samarium-153 Lexidronam.