ROCKVILLE, Md. ( TheStreet) -- Human Genome Sciences ( HGSI) said sales of its lupus drug Benlysta totaled $18.8 million in the third quarter, shy of investor expectations. The $18.8 million in Benlysta revenue excludes $2.5 million in gross-to-net adjustments, the company said. Investors and analysts were expected Benlysta sales of between $20 million and $21 million in net sales of the lupus drug in the September quarter. Human Genome Sciences shares at Tuesday's close of 12.73 remain near their lowest level in more than two years due to sharply lowered commercial expectations for Benlysta. Since launching in March as the first new lupus treatment approved by U.S. regulators in 50 years, investors have grown increasingly skeptical of Benlysta's potential to become a blockbuster drug due to questions about modest efficacy, reimbursement hurdles and surveys suggesting lackluster demand from both doctors and patients. Human Genome shares were trading down another 7% to $11.91 in the after-market. Sixty-five percent of buy-side investors said Benlysta will fail to reach $1.5 billion in sales by 2018, according to a recent investor survey conducted by ISI Group analyst Mark Schoenebaum. Human Genome shares Benlysta marketing responsibilities with its partner GlaxoSmithKline ( GSK). Human Genome did not offer Benlysta sales guidance for the remainder of the year, but said monthly sales are increasing slowly. During the four weeks of September, weekly gross sales averaged $2 million, up from $1.7 million and $1.4 million in August and July, respectively. "We are seeing solid progress in the trial and adoption of Benlysta treatment for systemic lupus by rheumatologists in the United States," said Human Genome CEO Tom Watkins, in a statement. Analysts, on average, are forecasting $80 million in Benlysta sales this year, including sales in Europe where the drug was recently approved and is being launched. But that's down from this summer when Benlysta was expected to bring in $90 million in 2011 sales. It remains to be seen whether analysts will reduce their Benlysta sales forecasts further given today's disappointing third-quarter report. Human Genome reported a net loss for the third quarter of $88.4 million, or 45 cents per share, compared with a net loss of $40.9 million, or 22 cents per share for the third quarter of 2010. Revenue in the third quarter was totaled $34 million, which includes sales from Benlysta and other products, compared to revenue of $50.8 million in the year-ago period. Analysts, on average, were expecting Human Genome to post a net loss of 39 cents a share on total revenue of $37.3 million. The company reduced its cash guidance for the year to between $440 million and $470 million from previous guidance of $550 million to $650 million. --Written by Adam Feuerstein in Boston. >To contact the writer of this article, click here: Adam Feuerstein. >To follow the writer on Twitter, go to http://twitter.com/adamfeuerstein. >To submit a news tip, send an email to: email@example.com.