Anthrax canceled the band's show Monday in Dallas as a result of a "medical concern."
The thrash metallers have been touring in celebration of their 40th anniversary alongside Black Label Society and Hatebreed, who still performed at the Dallas concert.
"We've waited so long to be able to celebrate our 40th anniversary," guitarist Scott Ian said in a statement. "[We] are so disappointed that we won't be able to do so [Monday] -- frankly, it blows."
Ian added, "Thank you for your support and understanding, and stay safe."
The tour is set to continue Tuesday in Austin, Texas.
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