Telomere length predicts neutrophil recovery in the absence of G-CSF after autologous peripheral blood stem cell transplantation

The Effect of Cancer Treatments on Telomere Length: A Systematic Review of the Literature

Background

It has been hypothesized that cancer treatments cause accelerated aging through a mechanism involving the shortening of telomeres. However, the effect of cancer treatments on telomere length is unclear.

Methods

We systematically reviewed the epidemiological evidence evaluating the associations between cancer treatment and changes in telomere length. Searches were performed in PubMed for the period of January 1966 through November 2016 using the following search strategy: telomere AND (cancer OR tumor OR carcinoma OR neoplasm) AND (survivor OR patient). Data were extracted and the quality of studies was assessed.

Results

A total of 25 studies were included in this review. Ten were solid cancer studies, 11 were hematological malignancy studies, and 4 included a mixed sample of both solid and hematological cancers. Three of the 10 solid tumor studies reported a statistically significant association between cancer treatment and telomere length shortening, and one reported longer telomere length after treatment. Among the hematological cancer studies, three showed statistically significant decreases in telomere length with treatment, and two showed elongation. When these studies were rated using quality criteria, most of the studies were judged to be of moderate quality.

Conclusions

The findings from this review indicate that the effect of cancer treatment on telomere length may differ by cancer type and treatment as well as other factors. Definitive conclusions cannot be made based on the published literature, because sample sizes tended to be small; treatments, cancer types, and biospecimens were heterogenous; and the length of follow-up times differed greatly.

Effect of Recipient Age and Stem Cell Source on the Association between Donor Telomere Length and Survival after Allogeneic Unrelated Hematopoietic Cell Transplantation for Severe Aplastic Anemia

We previously showed an association between donor leukocyte relative telomere length (RTL) and post-hematopoietic cell transplantation (HCT) survival in patients with severe aplastic anemia (SAA) who received bone marrow grafts at ages <40 years. Here, we tested the generalizability of the prior findings in an independent validation cohort and by recipient age and stem cell source in the combined discovery and validation cohorts. We used monoplex quantitative real-time PCR to measure RTL in: (1) a new SAA validation cohort of 428 patients (age range, .2 to 77 years) with available pretransplantation donor blood samples in the Center for International Blood and Marrow Transplant Research repository, and (2) 278 patients from the original cohort who had sufficient DNA to repeat RTL testing. We used Cox proportional hazard models to calculate hazard ratios (HRs), and 95% confidence intervals (CIs) across categories of donor RTL. Data from the validation cohort showed no association between donor RTL and patient survival, but further analysis identified differences by recipient age and stem cell source as the likely explanation. In patients <40 years, the HR comparing longest with shortest and middle RTL tertiles = .75; 95% CI,  .44 to 1.30 versus HR = 1.05; 95% CI, .59 to 1.89 for patients ≥40 years, P interaction = .37. In bone marrow recipients, the HR = .68; 95% CI, .72 to 1.10 versus HR = 1.29; 95% CI, .64 to 2.62 for peripheral blood stem cell grafts; P interaction = .88. Analyses using data from the 2 cohorts showed a statistically significant survival benefit only in <40-year-old patients receiving bone marrow graft (HR comparing longest and middle RTL tertiles with shortest = .69; 95% CI, .50 to .95, P = .02). The study suggested that the association between donor RTL and post-HCT outcomes in recipients with SAA may vary by recipient age and stem cell source. A larger study is needed to account for multiple comparisons and to further test the generalizability of our findings.

Predicting 5-fluorouracil toxicity in colorectal cancer patients from peripheral blood cell telomere length: a multivariate analysis

BACKGROUND

Identifying various pretreatment factors that predict chemotherapy-induced toxicity in colorectal cancer (CRC) patients undergoing treatment for their disease is crucial to optimising patient care.

METHODS

Seventy-three patients received adjuvant 5-fluorouracil (5FU)/leucovorin using either the Mayo Clinic (n=42) or a weekly schedule (n=31) and evaluated for clinical toxicity. Pretreatment blood analysis included measures of plasma uracil and dihydrouracil, peripheral blood mononuclear cell (PBMNC) telomere length (TL), standard biochemistry and cell differential analysis. On the first day of treatment 5FU-pharmacokinetic variables of area under the curve, half life and clearance were also measured. These variables together with age and gender were used in univariate and multivariate analysis as predictors of clinical toxicity.

RESULTS

For the Mayo schedule the primary toxicities were neutropenia (69%), mucositis (58%) and leukopenia (46%), with 70% of patients presenting with haematological toxicity ≥grade 1 (neutropenia and/or leukopenia). Multivariate analysis showed that haematological toxicity was predicted by short TL, high platelet lymphocyte ratio (PLR) and low neutrophil count (R(2)=0.38, P<0.0006), whereas mucositis was predicted by age, TL and PLR (R(2)=0.34, P<0.001). For the weekly schedule diarrhoea predominated (16%), with female gender as the only predictive factor. Although measures of uracil metabolism correlated well with 5FU metabolism (r=0.45-0.49), they did not indicate abnormal pyrimidine metabolism in this cohort and not surprisingly failed to predict for 5FU toxicity.

CONCLUSION

Short TL of PBMNC and an increased PLR were strong predictors of mucositis and haematological toxicity in CRC patients undergoing 5FU treatment in the adjuvant setting.

The importance of the telomere and telomerase system in hematological malignancies

Telomeres are specialized chromosomal end structures composed of repeat TTAGGG sequences in humans. They shorten with each cell division and thus serve as the "mitotic clock" of the cell. One of their main functions is the maintenance of chromosomal integrity and their excessive shortening is associated with DNA instability. Telomerase, a unique reverse transcriptase, is inactive in most somatic human cells and is up-regulated in most cancer cells. Recently, the biology of the telomere/telomerase system has attracted much attention because of its possible role in carcinogenesis and aging. In this article we review the biology of this system and its relevance to normal and malignant hematopoietic cells. The biological, diagnostic and prognostic value of telomere/telomerase biology is discussed, as well as its potential future applications in cancer therapeutics.