TREX1 and nasopharyngeal carcinoma: Sequencing of extrachromosomal DNA from one of the TREX1-deficient NPC lines, its isogenic control, and an RTi-treated TREX1-deficient line, showed that extrachromosomal L1 DNA was abundant when TREX1 was inactive, and in particular, there was 70% more L1Hs in the TREX1- deficient line compared with the control.