Studies have shown that male infertility is associated with a slightly increased risk for various types of cancer,including testicular cancer,possibly because of shared genetic factors. About one in six infertile men have azoospermia,or no viable sperm in their ejaculate,and these men may be at the highest cancer risk,a new study shows. For the study,researchers evaluated 2,238 men,average age 36,at a fertility clinic in Texas; 451 had azoospermia. They found 29 cases of cancer during an average follow-up of almost seven years. Over all,those in the infertile group were 1.7 times as likely as the general population in Texas to develop some form of cancer. But the risk more than tripled for those with azoospermia. While the increase in relative risk is substantial,the authors write,the absolute risk of cancer in this population remains low.