Shares of Spectrum Pharmaceuticals Inc., a maker of cancer medicines, plunged as much as 44 percent after the drugmaker said full-year sales would fall far short of analysts’ estimates.

Shares declined to $7.95 at 5:49 p.m. New York time Tuesday in extended trading, after closing at $12.43. The Henderson, Nevada-based company's stock dropped as low as $7 after the forecast was released.

Annual 2013 revenue will be $160 million to $180 million, Spectrum said today in a statement. Analysts anticipated total revenue of $297 million, according to the average of five estimates compiled by Bloomberg. The company said sales of its top product, Fusilev, will be $80 million to $90 million.

Spectrum cited shifting ordering patterns for Fusilev, an injection known chemically as levoleucovorin, as well as the increased use of generic drugs by hospitals, for the sales forecast.

Fusilev first won FDA approval in 2008 for patients with a bone tumor called osteosarcoma. The agency two years ago cleared the drug as a treatment for patients with advanced colon cancer. The treatment generated $204 million in sales last year, Spectrum reported.