(Reuters) - Shares of Aeterna Zentaris Inc jumped nearly 20 percent on Friday after the Canadian drugmaker said it has agreed with U.S. regulators on the design of a late-stage trial for its endometrial cancer treatment.

Aeterna said it plans to enroll about 500 patients in the Phase III, open-label trial comparing its treatment, AEZS-108, with a mainstream chemotherapy drug, doxorubicin.

The trial has been granted a "special protocol assessment" by the U.S. Food and Drug Administration, which indicates the agency is on board with the trial's design and means the drug is more likely to be approved if the trial succeeds.

The intravenous drug, which is also in earlier-stage trials for prostate, breast and bladder cancer, is a combination of doxorubicin and another chemical. Aeterna says AEZS-108 does less damage to healthy tissue than existing treatments.

Disappointing trial results for another cancer drug, perifosine, have weighed heavily on Aeterna's stock this year, and in October it consolidated its shares on a six-to-one basis.

Aeterna's Nasdaq-listed shares rose 18.5 percent to $2.57. In Toronto, the stock was up 18.5 percent at C$2.56 in late morning but was still down more than 70 percent for the year to date.

($1 = $0.99 Canadian)

(Reporting by Allison Martell; editing by John Wallace)