Give and take.

There is a lot of potential in using radiation as an adjunct to immunotherapy, primarily via inducing tumor antigens. Too bad radiation also causes lymphopenia, diminishing the immunotherapy troops. This retrospective review assessed the impact of palliative radiation on lymphocyte counts among patients treated with immune checkpoint inhibitors for metastatic non-small cell lung cancer, melanoma or renal cell carcinoma. As expected, the biggest drops in absolute lymphocyte counts occurred with radiation regimens of >5 fractions and when treating areas with lots of marrow like the spine, mediastinum or ribs. Also as expected, “severe” lymphopenia (absolute count <500) was associated with worse survival after initiating immunotherapy (HR 2.1). The authors correctly—if not novelly—conclude that (1) radiation is associated with lymphopenia and (2) lymphopenia is associated with worse survival. And let us hear all those who’ve taken philosophy 101 say it together now: Correlation doesn’t equal causation. TBL: We've still got a lot to learn on how best to synergize radition and immunotherapy. | Pike, Int J Radiat Oncol Biol Phys 2018