GT Biopharma is trading 5.44% lower at $6.43; no company-specific announcement confirms a reason for the October 13 decline. - Latest investor-relations news is dated September 15; a market-news source lists no October 13 headlines. - An October 9 registration lets existing holders sell up to 13.5 million shares; the company is not selling, and no source ties it to the drop. - The biotech ETF is down 2.01%, providing sector context but not explaining this individual move.