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In this issue of Cancer Discovery, a puzzling finding is reported that has divergent clinical implications: PD-1 inhibitors make cytotoxic T lymphocytes secrete a Wnt pathway suppressor to the blood that opens the blood\u2013brain barrier, both allowing circulating tumor cells to enter the brain and a chemotherapeutic to better reach tumor cells in brain metastases.<\/jats:p>\n                  <jats:p>See related article by Deo et al., p. 976<\/jats:p>","DOI":"10.1158\/2159-8290.cd-26-0417","type":"journal-article","created":{"date-parts":[[2026,5,1]],"date-time":"2026-05-01T07:11:03Z","timestamp":1777619463000},"page":"831-833","update-policy":"https:\/\/doi.org\/10.1158\/crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Checkpoint Breaches: Unexpected Effects of Anti\u2013PD-1 Therapy on the Blood\u2013Brain Barrier"],"prefix":"10.1158","volume":"16","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-0074-5945","authenticated-orcid":false,"given":"Matthia 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