For example, subsets of cells may harbor mutations in genes like EGFR, PTEN, or TP53, while others do not.20 In keeping with this, Brown et al. showed that in recurrent tissue adjacent to the T-cell injection site, IL13Rα2 expression was decreased compared to pre-therapy levels, suggesting that the recurrence/progression of patients was due to IL13Rα2-negative or low tumor cells.14 Here, PTEN is linked to neoplasm.