Stereotactic Radiosurgery for Sarcomas Spread to Spine

Nick Mulcahy

April 08, 2014

Single-fraction image-guided stereotactic radiosurgery (IG-SRS) should be considered as a first-line therapy for metastatic sarcomas of the spine, according to a new, single-center study.

The 88-patient study is the largest series to date of patients with a sarcoma that had spread to the spine, which was then treated with IG-SRS, say the authors, led by Yoshiya Yamada, MD, of the Department of Radiation Oncology at Memorial Sloan Kettering Cancer Center in New York.

Whether it was single-fraction or hypofractionated, IG-SRS provided "excellent" local control among these patients, all of whom had aggressive disease and poor prognosis, they report.

The outcomes are better than have been seen historically with conventional radiation. The authors believe that the new results should shake up the notion that IG-SRS is a "technique reserved for salvage therapy."

Their paper appears in the April edition of the International Journal of Radiation Oncology/Biology/Physics.

Twelve months after IG-SRS, overall local control was 87%.

However, notably, single-fraction IG-SRS provided significantly better 12-month local control than hypofractionated IG-SRS (90.8% vs 84.1%; P = .007). Thus the authors championed single-fraction as the method of choice for clinicians using IG-SRS in this setting.

The local control rates for both IG-SRS techniques are better than rates of 50% to 77% at 1 year seen historically with conventional radiotherapy, the authors say.

"Conventional radiation treatment for sarcoma metastatic to the spine provides sub-therapeutic doses, resulting in poor durable local control," they write.

Conventional radiotherapy in this setting consists of 20 to 40 Gy in 5 to 20 fractions at 2 to 5 Gy per fraction.

Despite their enthusiasm for the results, the authors also urge caution. "With a median follow-up time of 12.3 months, conclusions drawn from this study should be applied cautiously, especially in terms of toxicity," they write.

However, at the point of 1 year, the toxicity was not severe. Treatment was "well tolerated," with 1% acute grade 3 toxicity, 4.5% chronic grade 3 toxicity, and no grade > 3 toxicities.

Pain From Spinal Metastases

Sarcomas spread to the spine in 10% to 30% of cases, Dr. Yamada told Medscape Medical News in an email.

"Sarcomas are a highly variable group of malignant diseases, and metastasize to the spine at variable rates, depending upon the subtype of sarcoma," he explained.

Nonetheless, there is a rule of thumb in clinical practice. "Often low grade tumors are less likely to metastasize, while high grade tumors are very likely to metastasize," he said.

A variety of histologic subtypes of sarcomas were included in the new study. The investigators only excluded patients with pediatric sarcomas, chordomas, and primitive neuroectodermal tumors/Ewing sarcomas.

A sarcoma that spreads to the spine has a "disproportionate impact" on quality of life due to the related morbidity, high recurrence rate, and mortality burden, the authors point out.

"The clinical manifestations of sarcoma spine metastases are most commonly pain, as well as neurologic compromise for more advanced spine lesions. Pain is usually manifest as either biologic pain, mechanical instability pain, or both," Dr. Yamada said.

Further Details

The hypofractionated IG-SRS consisted of 3 to 6 fractions with a median dose of 28.5 Gy and was delivered to 43.3% of the patients. The single-fraction IG-SRS had a median dose of 24 Gy, and was delivered to 56.7% of the patients.

Overall survival was 60.6% at 12 months and median survival was 16.9 months.

The superior local control seen with single-fraction IG-SRS retained its statistical significance on multivariate analysis, the authors report.

It was the only variable that did so. A variety of variables were not found to be significant predictors of local failure, both in the univariate and multivariate analyses. These factors included histologic subtype, burden of disease, prior radiation, chemotherapy, and prior surgery as a treatment.

The authors explain that IG-SRS has historically been employed in last-ditch efforts with patients.

At Memorial Sloan Kettering, hypofractionated and single-fraction IG-SRS techniques were initially designed and implemented as salvage regimens for sarcomas and other radiation-insensitive histologies, they write.

But the "promising" new results "justify consideration of incorporating the technique into definitive treatment strategies," the authors write.

Int J Radiation Oncol Biol Phys. 2014;88:1085-1091.

Dr. Yamada is a consultant for Varian Medical Systems. Other authors also have financial ties to industry.

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