(Corrects attribution in second paragraph, to "sources," not Medivation)

By Deena Beasley

July 6 (Reuters) - Medivation Inc, which has opened its books to potential buyers, on Wednesday said its experimental cancer drug talazoparib is likely the best in a new class known as PARP inhibitors and pivotal trial data could be reported earlier than planned.

The San Francisco-based company on Tuesday agreed to provide information to Sanofi SA after rejecting the French pharmaceutical company's latest bid of $58 a share, plus $3 per share in the form of a contingent value right (CVR) relating to talazoparib sales. Medivation has also signed confidentiality pacts with Pfizer Inc and Celgene Corp, sources have previously told Reuters.

Medivation, known chiefly for prostate cancer drug Xtandi, is conducting a Phase III trial of talazoparib in patients with breast cancer linked to a mutation in BRCA genes, with initial trial data expected in the first half of next year.

After recent robust trial results for rival Tesaro Inc's PARP inhibitor niraparib, Medivation is considering the option of an earlier data read out, Chief Executive David Hung said on a conference call.

PARP inhibitors are designed to kill cancer cells by exploiting defects in a tumor DNA repair pathway. The only approved drug in the class is AstraZeneca Plc's Lynparza, also known as olaparib. Other experimental PARP inhibitors include Clovis Oncology Inc's rucaparib and AbbVie Inc's veliparib.

Hung summarized data backing up his belief that talazoparib is the most potent PARP inhibitor, the best "PARP trapper," has the most convenient dosing schedule and a competitive safety profile, given a superior ability to select its target.

He also said talazoparib could be effective against a broad range of tumor types.

Medivation acquired talazoparib last year from Biomarin Pharmaceutical Inc for up to $570 million and royalty payments based on future sales.

Wall Street analysts said the sale made sense for Biomarin, which specializes in rare diseases, not oncology. While talazoparib appeared to be a potent PARP inhibitor, "the Phase II data is similar to that produced by other PARPs, and therefore its differentiation is unclear," Cowen and Co said in an August 2015 research note.

Hung did not address the buyout offers on Wednesday's call.

Sanofi previously used a CVR in its 2011 acquisition of Genzyme Corp, which at that time was developing multiple sclerosis drug Lemtrada. Under that merger agreement, Sanofi issued Genzyme shareholders tradable certificates entitling them to payments if Lemtrada won approval from the U.S. Food and Drug Administration by March 31, 2014, and further payments if it met certain sales benchmarks after that.