Regeneron Pharmaceuticals Inc. (REGN) - Get Report shares had a surprisingly stellar day even thought investors learned Swiss pharma giant Novartis could soon be a rival to the drug that drives most of Regeneron's revenue.

Instead, Regeneron's stock rose $23.66, or 5.02%, to $495.33 on Tuesday, June 20 despite the announcement of test results for Novartis AG's (NVS) - Get Report treatment for macular degeneration.

The investor rally is likely due to the strong launch for Dupixent Regeneron's treatment for severe atopic dermatitis. Sales for treating U.S. adult are predicted to be $951 million by 2023. It is also being tested as an asthma treatment.

Regeneron was not available for immediate comment.

Swiss-based Novartis released data from its RTH258 clinical trials illustrating that RTH258 does not need to be injected as often as Regeneron's counterpart, Eylea, to treat neovascular AMD, a leading cause of vision loss. 

As of now, the only difference between the two medications is the injection frequency.  Indications are that treatment efficacy between the two drugs is equal.

Regeneron recognizes the strong competition Eylea faces. In their most recent 10Q, Regeneron cites the collaboration between Novartis AG and Genentech/Roche for various eye treatments as a risk factor. The advancement of Novartis' RTH258 could launch the treatment into U.S. markets and drain Regeneron's Eylea revenue. 

And according to Eric Althoff, head of Global Media Relations at Novartis, the company intends to extend its commercial reach into the U.S. neovascular AMD market.

"Based on these robust data, we are looking forward to working with regulatory agencies to bring this pioneering treatment to patients," said Althoff. "We will pursue advancing RTH258 in a number of additional indications, including DME and RVO. We intend to commercialize RTH258 globally, including the U.S."

But Jefferies analyst Biren Amin hinted that the data may not be as comprehensive as Novartis suggests.

"The Novartis data looked good from a top-line standpoint, [but] there was probably some critical details that the press release is missing," said Amin. "For example, with the vision acuity scores and the differences between the two arms. The press release didn't provide disclosure on that and I guess we'll have to wait for the complete data to be reported at the American Academy of Ophthalmology."

Amin added that there is potential for manufacturing problems since Novartis is filing its drug drug approval request in 2018. Due to the delay, Amin projects that Novartis isn't much of concern to Regeneron -- for now, that is.

"You don't have a drug filing until 2018, which means that the product won't be available until 2019, so it [RTH258] won't affect Regeneron until maybe 2020," said Amin.