The influence of histology on the response of brain metastases to gamma knife radiosurgery: a propensity score-matched study

In terms of response to fractionated radiotherapy, metastatic brain tumors of certain origins are considered radioresistant.

To determine the influence of “radioresistant” histology on outcomes of brain metastases treated with radiosurgery.

Between 2001 and 2017, 121 patients with brain metastases from renal cell carcinoma (RCC) and 2151 from non-small cell lung cancer (NSCLC) were reviewed. Eighty-seven pairs were derived using propensity score matching. Local progression-free survival (PFS), progression patterns, distant PFS, and overall survival were investigated.

The median follow-up period was 13.7 months (range, 1.6–78.4 months). A total of 536 lesions were treated using gamma knife radiosurgery (GKS), with a median dose of 20 Gy (range, 12–28 Gy). The actuarial local PFS rates in the RCC group were 91% and 89% at 6 and 12 months, respectively, and did not differ from the NSCLC group (97% and 83% at 6 and 12 months, respectively). Continuous progression, without response to GKS, was noted in seven of the eight progressed RCCs. However, six of the seven progressed NSCLCs showed transient shrinkage before progression. The median distant PFS was 9.3 months (95% CI, 6.3–12.2) in the RCC group and 8.0 months (95% CI, 5.5–10.4) in the NSCLC group. The median overall survival was 16.1 months (95% CI, 11.3–20.8) and 14.9 months (95% CI, 11.9–17.8) in RCC and NSCLC groups, respectively.

Histological differences had no effect on local control in the single high-dose range used for radiosurgery. However, changes in tumor volume during progression varied across tumor histology.