The findings prompt the authors to ask whether boys with the condition should be regularly monitored to lessen the potential risk

Cryptorchidsim, where testes fail to descend into the scrotum and are retained within the abdomen, is the most common birth defect in boys, affecting around 6% of newborns.

The authors trawled the Embase and Medline databases for studies, which looked at the potential link between cryptorchidism as an isolated abnormality and testicular cancer risk, and which had been published between January 1980 and December 2010.

They found 735 relevant papers, published in English, among which 12 studies matched the inclusion criteria and covered corrective surgery (orchidopexy).

The haul included 9 case-control studies, involving 2281 cases of testicular cancer, which had been diagnosed between the ages of 15 and 75 between 1965 and 2006, and 4811 controls.

And it included 3 cohort studies, which regularly monitor similar groups of people over the long term to see what happens to them.

These studies involved more than 2 million boys whose health was tracked for a cumulative period of 58 million person years. Boys with cryptorchidism who developed testicular cancer totalled 345.

Boys with cryptorchidism in the case-control group were almost 2.5 times as likely to develop testicular cancer as those without the condition.

And those in the cohort studies were almost 4 times as likely to develop the disease if their testes had not descended at birth.

The authors calculated that, on the basis of the two sets of figures, boys with isolated cryptorchidism are almost three times as likely to develop testicular cancer in later life.

Testicular cancer is the most common cancer in men aged between 20 and 45, and rates have increased substantially worldwide over the past few decades, the authors point out.

In the UK, the number of new cases almost doubled between 1975-7 and 2006-8, rising from 3.4/100 000 men to 6.9/100 000.

"Many important unanswered questions remain, such as how laterality, degree of descent, and surgical correction affect the malignant potential of the [undescended] testis," write the authors.

And they add: "The most poignant question this study raises, however, is whether the risk of malignant transformation is sufficiently significant to warrant regular follow-up, as is the case with other premalignant states."