Cyberknife radiosurgery for breast cancer spine metastases: a matched-pair analysis

There are few options for breast cancer patients with spinal metastases recurrent within a previous radiation treatment field. CyberKnife radiosurgery has been used in our institution to treat such patients. To evaluate their outcomes, as there are no comparable radiation treatment options, the outcomes were compared between 18 patients with spinal metastases from breast cancer treated with CyberKnife stereotactic radiosurgery, 17 of which had prior radiotherapy to the involved spinal region and were progressing, and 18 matched patients who received conventional external beam radiotherapy (CRT) up-front for spinal metastases.

Radiosurgery was delivered in 3 to 5 fractions to doses ranging from 2100 to 2800 cGy. Women were matched to patients in a CRT group with respect to time from original diagnosis to diagnosis of metastases, estrogen receptor / progesterone receptor (ER/PR) status, presence or absence of visceral metastases, prior radiotherapy, and prior chemotherapy. Survival and complications were compared between treatment groups. Surviving patients were followed out to 24 months.

The CyberKnife and CRT groups were comparable along all matching dimensions and in performance status before treatment. Outcomes of treatment were similar for patients in both groups; ambulation, performance status, and pain worsened similarly across groups posttreatment. Survival and the number of complications appeared to favor the CyberKnife group, but the differences did not reach statistical significance.

The statistical comparability of the CyberKnife and CRT groups reflects the small sample size and stringent requirements for significance of the matched-pair analysis. Nevertheless, comparability in these difficult cases shows that salvage CyberKnife treatment is as efficacious as initial CRT without added toxicity.