Oct 28 (Reuters) - Gilead Sciences Inc (GILD.O) on Thursday posted higher-than-expected third-quarter earnings on strong demand for its COVID-19 antiviral treatment, but said 2021 sales of its other drugs will fall short of earlier estimates. Without Veklury, also known as remdesivir, Gilead said it now expects sales for the full year of around $21.5 billion. That is down from its previous mid-point estimate of $21.8 billion, reflecting the longer than expected impact of the pandemic on its business. Gilead has said that sales, particularly of its flagship HIV drugs, have been hurt during the pandemic as many people avoided healthcare settings. The biotechnology company also said results from a key trial of its drug Trodelvy in patients with a specific type of breast cancer have been delayed from this year until at least late January. The medication was the main driver of Gilead"s $21 billion purchase of Immunomedics last year. "Nothing has changed in regard to our confidence", Chief Executive Daniel O"Day said about the trial, on a conference call. The company"s shares, which closed at $67.34, were down 2.1% at $65.95 in extended trading. Gilead reported adjusted quarterly earnings of $2.65 per share, soundly beating Wall Street estimates of $1.75 per share, as compiled by Refinitiv. Revenue for the quarter rose 13% from a year earlier to $7.4 billion, ahead of the average analyst estimate of $6.26 billion. But the outperformance was almost entirely driven by sales of Veklury, which more than doubled to $1.9 billion for the quarter. Gilead"s results were described as "mixed" by Jefferies analyst Michael Yee. Aside from Veklury, "key product line items were generally flattish to lower," he said in a research note. Use of Veklury, given intravenously to people hospitalized with COVID-19, is driven by pandemic hospitalization rates, which peaked in August and have been falling ever since, Gilead Chief Commercial Officer Johanna Mercier said. Third-quarter sales of Gilead"s HIV medicines dropped 8% to $4.2 billion as some drugs lost a patent protection and the pandemic continued to limit visits to doctors. Sales of Trodelvy came in at $101 million for the quarter, in line with analyst estimates. Gilead raised its full-year adjusted earnings forecast to $7.90 to $8.10 per share from its prior projection of $6.90 to $7.25. Including Veklury, the company said it now expects product sales for the year of $26 billion to $26.3 billion, up from a previous estimate of $24.4 billion to $25 billion. Reporting By Deena Beasley Editing by Bill Berkrot and Karishma Singh