Mechanisms that drive telomere maintenance and recombination in human cancers

Telomere maintenance is essential for the continued proliferation of mitotically active cells. Alternative Lengthening of Telomeres (ALT) is a recombination-dependent pathway of telomere maintenance analogous to break-induced replication (BIR) [1] that becomes activated in approximately 10–15% of human cancers. ALT is prevalent in tumours of mesenchymal or neuroepithelial origin, and typically confers a poor prognosis. The aggressiveness and lack of effective strategies to treat these cancers make the ALT pathway a compelling potential therapeutic target to prevent tumour formation and/or the appearance of secondary malignancies after conventional chemotherapy [2]. While the precise initiator of ALT during tumourigenesis remains elusive, substantial progress has been made in interrogating the underlying homology-directed repair mechanisms that converge at telomeres to enable telomere length maintenance. Here, we describe recent advances in our understanding of the ALT mechanism and highlight potential therapeutic targets that may offer future promise in the treatment of ALT cancers.