Bartolo Colon has failed an MLB-issued drug test and has been suspended for 50 games, reports Jon Heyman of CBSSports.com. Both the Athletics and MLB have confirmed the suspension. Tim Brown of Yahoo! Sports says (on Twitter) that he tested positive for testosterone.

Colon, 39, resurrected his career last season after undergoing an experimental stem cell treatment on his injured shoulder, a procedure MLB investigated last summer. Colon is scheduled to become a free agent after the season.

The veteran right-hander has pitched to a 3.43 ERA with 5.4 K/9 and 1.4 BB/9 in 24 starts and 152 1/3 innings for the Athletics this season after signing a one-year, $2MM contract. After missing all of 2010 and most of the 2006-2009 season, the 2005 AL Cy Young Award winner resurfaced with the Yankees last season and posted a 4.00 ERA in 164 1/3 innings.

Brett Anderson returned to the Athletics' rotation last night, pitching seven innings and allowing one earned run. He projects to join Brandon McCarthy, Tommy Milone and Jarrod Parker in the rotation for the remainder of the season. Dan Straily, Tyson Ross and Travis Blackley are also rotation options for the Athletics, who are deep enough in starting pitching to withstand the loss of Colon.