What happened

Seattle Genetics (NASDAQ:SGEN) is up 9.5% as of 11:27 a.m. EDT today after releasing first quarter earnings after the bell yesterday and offering up strong second-quarter guidance.

So what

Sales of Seattle Genetics' only drug, Adcetris, jumped 36% year over year to $95.4 million. Royalties, which are primarily from sales of Adcetris outside the U.S. and Canada by its global partner Takeda, came in at $15.7 million, down a little compared to the year-ago quarter, but that was just due to the new accounting standards for revenue recognition.

Adcetris sales growth in the U.S. is coming from an expanded approval in late March for use of Adcetris in newly diagnosed patients with Hodgkin lymphoma based on data from the Echelon-1 trial. The drug had been approved for use later in the treatment paradigm for Hodgkin lymphoma patients, but an approval for earlier use results in more potential patients.

The year-over-year growth also benefited from an FDA approval last November for patients with two subtypes of cutaneous T-cell lymphoma (CTCL). Some CTCL patients were already getting the drug off-label, but management still noted that it's adding some additional sales.

Management wasn't willing to give new 2018 guidance, which seems reasonable given the expanded approval, but did give guidance for Adcetris sales in the second quarter of $105 million to $110 million, which would be a solid 11% to 16% growth over the first quarter.

Stained micrograph of purple cancer cells.

Image source: Getty Images.

Now what

Seattle Genetics just needs to keep firing along, capturing patients in these new indications.

The next large potential approval for Adcetris will come from the phase 3 Echelon-2 trial in newly diagnosed patients with peripheral T-cell lymphomas, which is due out sometime this year.

And of course, investors will eventually want to see that the company isn't just a one-trick pony. Fortunately Seattle Genetics has multiple drugs -- enfortumab vedotin and tisotumab vedotin -- that are currently in or ready to enter pivotal trials that could get the drugs approved by the FDA.

Brian Orelli has no position in any of the stocks mentioned. The Motley Fool recommends Seattle Genetics. The Motley Fool has a disclosure policy.