Re-evaluating brain metastases radioresistance in the modern era: a retrospective cohort study

Radiation therapy (RT) is a cornerstone of intracranial metastatic disease (IMD) treatment. Historically, IMD from melanoma, renal cell, gastrointestinal (GI), colon, thyroid cancers and sarcomas were considered radioresistant. The advent of stereotactic radiation therapy (SRT) relative to whole brain radiation therapy (WBRT) prompts reconsideration of this categorization. Patients with a primary cancer diagnosis who received cranial RT were identified and grouped based on primary tumour type into breast, lung, radioresistant and other. Hazard ratios (HR) of overall survival (OS) were compared between patients receiving SRT or WBRT, and between primary cancer categories relative to the breast cancer group. The median OS of the cohort was 6.05 months (9.17 vs. 3.02 months for SRT vs WBRT). Of patients treated with SRT or WBRT, median OS based on primary cancer type were 13.9 vs. 3.1 months (p < 0.001) in breast, 9.4 vs. 3.5 (p < 0.001) in lung, 9.2 vs. 2.5 (p < 0.001) in radioresistant, 3.6 vs. 3.7 (p = 1.0) in colon/GI, and 6.9 vs. 2.2 (p < 0.001) in other. Our study found differences in IMD patient OS based on SRT vs WBRT treatment, except for colon cancer patients, suggesting that definitions of radioresistance may be dependent on RT technique.