Biopharmaceutical company Amarin is "just getting started" in treating cardiovascular patients, CEO John Thero told CNBC on Wednesday.

Shares have surged more than 660 percent in the last six months on the hopes the company's omega-3 capsule, Vascepa, will be approved for additional uses. It is already being used to treat patients with very high triglycerides — but a clinical trial has also shown it reduced the risk of serious cardiovascular events in statin-treated adults with elevated risk.

"We just doubled the size of our sales force. We will be applying next month to the FDA to get the expanded label," Thero said on "Power Lunch." "Assuming we get approved there, we'll further expand our sales force. There's tens of millions of patients who can potentially benefit from this therapy."

In its earnings release on Wednesday, Amarin reaffirmed its guidance for 2019. It expects net revenue to grow by more than 50 percent over 2018, to reach $350 million this year. The potential label expansion isn't included in that figure because the company doesn't expect an answer from the FDA until late 2019 or early 2020.

The clinical trial showed Vascepa "could help improve heart health even more" for those patients already on traditional statins, Thero said. Statins lower cardiovascular risks by 25 percent to 35 percent, he said.

"What we have shown is that in those patients who already have their cholesterol well managed, that we can lower that risk by another 25 percent and lower the risk of death by 20 percent," he said. "So this is sort of a new paradigm in cardiovascular health management."

Thero also stressed that the company wants to keep the drug affordable, pointing out that it is priced at about one-fifth of what recent launches of new products in the cardiovascular market cost. "By making it affordable, more and more patients can use it." For patients with insurance, it should cost about $9 a month, he said.

"We really think we're just getting started. Just like statins took a while — really over more than a decade to grow — but now treat about 40 million patients, there's about an equal number of patients who can potentially benefit from Vascepa."