Some human sarcoma subtypes use the telomerase-independent telomere maintenance mechanism (TMM) alternative lengthening of telomeres (ALT) more frequently than other cancers to overcome senescence. Previously, ALT activity was identified in 6/64 various canine sarcomas including 2/5 (40%) histiocytic sarcomas (HS). The aim of this retrospective study was to analyze the prevalence of ALT in a larger canine cohort of HS including a sub-cohort of Bernese Mountain dogs (BMDs).

Sixty-seven dogs with HS including 50 BMDs from two centers were evaluated. ALT-positive canine and human tumor samples served as controls. DNA was extracted by commercial-kit (Nexttec) from archived formalin-fixed paraffin-embedded (FFPE) samples submitted for routine diagnostic and quantified by fluorescence dye. ALT activity was examined through extrachromosomal telomeric DNA-circles using radiolabel C-circle (CC) assay. Following published recommendations, after background correction and normalization on input DNA signals of abundant Alu-elements, levels above 5-fold background were defined as ALT-positive and between 2-to 5-fold as borderline.

Samples of two BMDs showed weak ALT activity 5.1 and 5.5-fold above background compared to 232-fold above background detected from control human osteosarcoma cell line U2OS. Two non-BMD-samples revealed borderline ALT-positive signals of 2.2-fold above background each. Other samples were ALT-negative. Positive controls showed CC-signals in expected ranges, important to exclude false-negatives.

The results indicate contrary to the previous study that HS seem to use weak ALT activity with prevalences of 4% in BMDs and ≤9% in other breeds. Future studies may demonstrate high prevalence of the other TMM telomerase activity with potential as prognostic marker and therapeutic target.

Disclosures

No disclosures to report.