Telomeric DNA-Promyelocytic Leukemia (TEL-PML) Colocalization as an ALT Proxy in Relation to Metastatic Behavior in Osteosarcoma: A Retrospective Cohort Study.

Osteosarcoma is the most common primary bone tumor in children, adolescents, and young adults, and metastasis remains the main determinant for a poor outcome. We conducted an exploratory retrospective cohort study using formalin-fixed, paraffin-embedded tissue from 97 patients with histopathologically confirmed osteosarcoma treated between 2005 and 2019 to evaluate telomere maintenance mechanisms. To assess alternative lengthening of telomeres (ALT), colocalization of telomeric DNA and promyelocytic leukemia protein (TEL-PML) was evaluated as a tissue-based proxy. TEL-PML colocalization was assessed using combined PML immunofluorescence and telomere DNA PNA-FISH. Furthermore, telomerase reverse transcriptase (TERT) expression was evaluated by immunohistochemistry in relation to metastasis and disease progression. Logistic regression models were adjusted for age, sex, and smoking. TEL-PML was evaluable in 45/97 cases, including 10 positive and 35 negative tumors; the remaining samples were non-evaluable because of non-determinable signal or predominant necrosis. TERT immunohistochemistry was scorable in 58/97 cases, of which 33 were positive. TEL-PML evaluability was associated with amputation specimens, whereas TERT positivity was associated with non-osteoblastic histology and was inversely associated with age. Neither TEL-PML nor TERT was significantly associated with metastasis, recurrence, or death. Exploratory time-to-metastasis curves suggested an earlier increase of metastatic events among TEL-PML-positive cases. However, the small number of positive tumors precludes definitive prognostic interpretation. These hypothesis-generating findings indicate that TEL-PML assessment is feasible in osteosarcoma, but it is strongly influenced by tissue adequacy. On the other hand, TERT immunohistochemistry appears to reflect subtype- and age-related heterogeneity rather than providing robust outcome stratification in this cohort.