Do brain mets grow while you wait? A volumetric natural history assessment of brain metastases from time of diagnosis to gamma knife treatment

Brain metastasis (BM) is a common neurologic complication of cancers such as lung, breast, and melanoma. Recently, there has been a shift in treatment of BM from whole brain radiation therapy to stereotactic radiosurgery (SRS) and the success is dependent on tumor volume. While most metastases grow over time, data on growth rate is lacking. Therefore, we document volume changes of metastases before treatment. We retrospectively reviewed MRI imaging records of 82 patients with a total of 294 BMs, treated in our cancer center by one neurosurgeon and one radiation oncologist with Gamma Knife SRS over a three-year period. We measured tumor volume at the time of diagnosis and compared with tumor volume on the day of treatment. Volumes were compared using the Wilcoxon signed-rank test. Lung, melanoma and breast made up the majority of metastases diagnosed. More than 75% of tumors grew and these changes in volume and percent changes in volume were statistically significant. Thirty percent of tumors doubled in size before treatment. Patients with the largest mean pretreatment tumor size were urgently treated within 6 days, yet still demonstrated the largest change in volume. This study is one of the first to document volume changes of brain metastases from the time of diagnosis to SRS treatment. Our results indicate that brain metastases can grow rapidly and it is imperative that we streamline patient management processes to minimize delays in treating patients with SRS, since outcomes are dependent on tumor size.