A C-circle assay for detection of alternative lengthening of telomere activity in FFPE tissue.

Alternative lengthening of telomeres (ALT) is a telomerase-independent, recombination-based telomere maintenance mechanism that allows cancer cells to acquire unlimited proliferative capacity. The C-circle assay (CCA) has emerged as the gold standard for quantitative measurement of ALT activity. Here, we present a modified CCA protocol to examine ALT activity in formalin-fixed paraffin-embedded specimens. We optimized several aspects of the procedure including genomic DNA isolation and hybridization steps, which allows for sensitive and robust quantitation of ALT activity in patient biopsies. For complete details on the use and execution of this protocol, please refer to Lippert et al. (2021).