Alberto Puello's A-sample revealed an adverse finding for the performance-enhancing drug clomiphene and its M1 and M2 metabolites, according to a Voluntary Anti-Doping Association letter obtained by ESPN on Wednesday.

Puello (21-0, 10 KOs) was scheduled to defend his WBA junior welterweight title against Rolly Romero on May 13 in Las Vegas, but sources told ESPN that fight is now cancelled as a result of the positive test for the banned substance.

Puello, a 28-year-old Dominican, could be stripped of his 140-pound title as a result. Romero (14-1, 12 KOs) is expected to remain in his PBC on Showtime headline slot on May 13, sources said, and could fight Ismael Barroso for the vacant title if Puello is indeed stripped.

Puello will have the opportunity to have his B-sample tested following the April 5 adverse finding.

"We're going through due process," WBA president Gilberto Mendoza told ESPN. "We're going to listen to Puello's arguments and let him disclose all the information. We'll send all his information to the medical and legal committee, and then we'll come back with an answer regarding his status as champion."

Victor Conte, the founder of BALCO, told ESPN in October that clomiphene is "a fertility drug that will raise testosterone by 50%." Conte spoke to ESPN after welterweight boxer Conor Benn tested positive for the same substance. Benn was later cleared of intentionally doping by the WBC. Conte served time in prison after pleading guilty to conspiracy to distribute performance-enhancing drugs before founding SNAC, a sports nutrition company.

Puello captured the WBA's vacant junior welterweight title in August with a decision victory over Batyr Akhmedov. Romero, a 28-year-old from Las Vegas, is coming off a TKO loss to Gervonta Davis in May at 135 pounds and was set to fight for a title in his 140-pound debut.