Label expansions for cancer drugs are pretty standard. Pfizer (NYSE:PFE), Onyx Pharmaceuticals (NASDAQ:ONXX), and Novartis (NYSE:NVS) are all seeking to expand sales of their already-approved cancer drugs by attempting to show that their drugs work for additional cancer types.

But Eli Lilly (NYSE:LLY) might have the best strategy of them all: Sell the drug to the same patients, just for a longer time frame. Today the company announced that the Food and Drug Administration had expanded the approval of its cancer drug, Alimta, to include maintenance therapy for nonsquamous, non-small cell lung cancer (NSCLC). In addition to being given with chemotherapy as a first-line therapy, Alimta is now approved for use over an extended period of time for patients who are responding to chemotherapy.

Eli Lilly managed to sell over $1.1 billion of Alimta last year, a solid 35% growth over the previous year. In the U.S., sales in 2008 grew 25% to $562 million. This new indication should help the drug maintain its steady climb upward.

It can use the help. Alimta has some competition now, such as Roche's Avastin, and Roche's and OSI Pharmaceuticals' (NASDAQ:OSIP) Tarceva, but there are several other companies trying to get approved to market their drugs to treat NSCLC. Onyx's Nexavar and Pfizer's Sutent are both in trials for NSCLC, and Eli Lilly, in combination with partner Bristol-Myers Squibb (NYSE:BMY), is working on getting Erbitux approved to treat NSCLC after results of a phase 3 trial showed extended survival that should be enough to get it approved.

Investors take note: Just because a drug is approved doesn't mean you can ignore it. Just like any other company, drugmakers try to expand the sales of their products. But unlike retailers, for instance, maintaining sales growth can be just as hard as getting the drug approved in the first place. Growing sales is usually a little easier for cancer drugs, but Eli Lilly seems to have found the easiest way yet.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool has a disclosure policy.