Transfection of ETCC001 human breast cells with hTERT. Five hTERT-transfected clones (ETCC006, ETCC007, ETCC008, ETCC010 and ETCC011) were obtained. (A) Telomerase activities were determined using TRAPeze-XL telomerase detection kit. Heat inactivated samples were used as negative controls and the readings were deducted as background. (B) Population doubling time (in hour) was determined using cell confluency as a measure of cell growth. Only log phase of the growth curve was used in the calculation of population doubling rate. (C) Colony counts of ETCC001 and hTERT-expressing cell lines in the soft agar assay. The assay was performed in triplicates and error bars represent standard deviation.