Interestingly, and unexpectedly, while TERT+/− (referred to as “TERT haploinsufficiency” interchangeably hereafter) and TERT+/+ clones were obtained, we were unable to establish any TERT homozygous knockout (TERT−/−) clones from any of these three types of cancer cells, indicating that TERT−/− tumor cells have extremely low survival rates in vitro. Here, TERT is linked to cancer.