July 07, 2010
Short Telomeres Markers For Higher Cancer Risk

The telomere caps on chromosomes shorten as you age. A prospective study finds shorter telomeres are linked to a higher risk of cancer.

Peter Willeit, M.D., of Innsbruck Medical University, Innsbruck, Austria, and colleagues conducted a study to assess the association between leukocyte telomere length and risk of both new-onset cancer and cancer death. Leukocyte telomere length was measured by quantitative polymerase chain reaction (laboratory technique used to analyze DNA) in 787 participants, free of cancer in 1995, and part of the prospective, population-based Bruneck Study in Italy. The primary outcomes analyzed included the incidence of new cancer and cancer mortality over a follow-up period of 10 years (1995-2005).

During follow-up, a total of 92 of 787 participants (11.7 percent) developed cancer. Analysis indicated that short telomere length at the beginning of the study was associated with new cancer independently of standard cancer risk factors. Compared with participants in the longest telomere length group, participants in the middle length group had about twice the risk of cancer, and those in the shortest length group had approximately three times the risk. Cancer incidence rates were inversely related to telomere length, with participants in the group with the shortest telomere length having the highest rate of cancer.

The obvious question: what's the direction of causality? I am guessing that short telomeres are not causing cancer. One possibility: cells that have shorter telomeres have lived tougher lives (metaphorically speaking) and are more damaged than cells in same age people who have longer telomeres. While that's probably true of the cells of the body as a whole I suspect another mechanism is at work with leukocytes. More on this below

It would be interesting to know whether short telomeres in leukocytes is well correlated with short telomeres in other cell types, especially in the cell types listed here as having become cancerous.

Short telomere length was also associated with a higher rate of death from cancer. "Of note, telomere length was preferentially associated with individual cancers characterized by a high fatality rate such as gastric, lung, and ovarian cancer, but less so with tumors linked to better prognosis," the authors write. They add that telomere length had a similar predictive value for cancer in both men and women and in various age groups.

So what's the other mechanism of causation I suspect? Leukocytes are white blood cells. In other words, immune cells. White blood cells do not just kill invading cells. The immune system also (sometimes) goes after cancer. Leukocytes with short telomeres are less able to divide and therefore are less able to mount an attack against cancer cells. It could be that short telomeres matter because they indicate an aged immune system that won't fight cancer.

Dr. Zheng Cui of Wake Forest University has found that some special mice and rare people have extreme anti-cancer immune systems. He has also found that the anti-cancer capability of immune systems decline with age. That decline in anti-cancer capability is due in part to immune cells losing the ability to divide due to worn down telomeres.

What we need to slash our risks of cancer: Rejuvenated immune systems.

Share |      Randall Parker, 2010 July 07 09:23 PM  Aging Immune System


Comments
Curt said at July 9, 2010 4:02 PM:

Bruce Ames has long considered that the number of times a cell has divided the most important predictor of the probability of cancer. From this, aging of course is a key factor, but so is chronic inflamation, which stimulates more rapid division. Whatever the cause, the more division, the fewer telomeres.

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