A protein that protects the body from tissue damage has also been found to increase the risk of tumors. Bcl-xL protein helps the body's healthy cells survive the effects of toxic chemotherapeutic agents .
The protein was also found to encourage the growth of tumors in mice following exposure to a carcinogen. The study compared the effect of urethane, a lung-specific carcinogen, on two sets of mice, which are genetically dissimilar with respect to the Bcl gene expression.
The strain of mice, which produced less Bcl protein, developed less number of tumors in contrast to mice that produced more of Bcl. Moreover, mice with more Bcl protein production on an average had larger tumours than it's counterpart.
The human Bcl-xL protein is functionally identical to the mouse protein, so the same effects are expected in humans. The Bcl protein expression is likely to be different in different individuals of a population.
In addition, Bcl-xL levels in each person are altered at times in response to certain stimuli. Therefore, it's possible that because of variation in Bcl-xL levels some individuals are more prone to developing tumors or more susceptible to tissue injury during their lifetime.