LONDON (Reuters) – a study showing that men who start to go bald at 20 may be more likely to develop prostate cancer in later life suggests they might benefit from early screening or preventative therapy, scientists said on Tuesday.

French researchers compared 388 men being treated for prostate cancer with 281 healthy men and found that those with the disease were twice as likely as the healthy men to have started losing their hair when they were 20.

If the men only started going bald when they were 30 or 40, there was no difference in their risk of developing prostate cancer compared to the healthy group.

"At present there is no hard evidence to show any benefit from screening the general population for prostate cancer. we need a way of identifying those men who are at high risk," said Philippe Giraud of Paris Descartes University, who led the study.

"Balding at the age of 20 may be one of these easily identifiable risk factors and more work needs to be done now to confirm this," he said in a statement.

Giraud, whose findings were published in the cancer journal Annals of Oncology, said men identified as at higher risk of prostate cancer could be selected for earlier screening, or for chemo-prevention therapy using so-called anti-androgenic drugs like Merck's Proscar, or finasteride.

Finasteride is used to treat both prostate enlargement symptoms and baldness. it blocks the conversion of testosterone to an androgen hormone called dihydrotestosterone, which is thought to cause hair loss.

GlaxoSmithKline has a drug in the same class called Avodart, or dutasteride, and is currently seeking approval from the United States Food and Drug Administration (FDA) for a license for use in men at higher risk of developing prostate cancer. But an FDA panel advised last month that GSK's application should be rejected.

Prostate cancer is the second most common cancer in men after lung cancer and kills an estimated 255,000 men each year.

Androgenic alopecia, also known as male pattern baldness, affects around 50 percent of men in their lifetime.

Previous studies have established a link between baldness and androgenic hormones, and androgens also play a role in the development and growth of prostate cancer.

Giraud and Michael Yassa of the University of Montreal in Canada, who also worked on the study, asked men to fill in a questionnaire about their history of prostate cancer, if any, and to indicate any hair loss they had at ages 20, 30 and 40 using pictures graded from stage I (no hair loss), to stage IV (receding hairline and balding from the top of the head).

The men's doctors also provided patients' medical histories, including any diagnosis of prostate cancer, age at diagnosis, stage of the disease and treatment. The study ran for 28 months.

"The data revealed that any balding at stages II-IV was associated with double the risk of prostate cancer later in life. this trend was lost at ages 30 and 40," said Yassa.

"Further work should be done, both at the molecular level and with larger groups of men, to find the missing link between androgens, early balding and prostate cancer."

(Editing by Sonya Hepinstall)