While insufficient processivity of the RT reaction may have led to an underestimation of the 5’ extension of lowly expressed transcripts in some cases, publicly available PACBIO and CAGE data from a gastric and a breast cancer cell line revealed that POU5F1B-encoding TcGTs were produced from LTR66 in the former and from downstream Alu or LTR33 integrants in the latter (Supplementary Fig. 6a). This evidence concerns the gene POU5F1B and breast carcinoma.