Don't mess with mother nature.. or crowded longs!

Crispr Therapeutics led gene-editing stocks lower after new studies published by Nature Medicine found that cells whose genomes are edited with the CRISPR-Cas9 technology have the potential to cause cancer, Stat News reports.

Editing cells’ genomes with CRISPR-Cas9 might increase the risk that the altered cells, intended to treat disease, will trigger cancer, two studies published on Monday warn — a potential game-changer for the companies developing CRISPR-based therapies.

Crispr fell as much as 14%; Editas Medicine and Intellia Therapeutics dropped as much as 9.5%; Sangamo Therapeutics slipped as much as 4.3%

The findings come as Crispr is preparing to start its first clinical study in people in Europe in the second half of the year; the FDA has paused the company’s plans to do a similar trial in the U.S.

Given the massive interest in this company and its gene-editing applications, Stat News asks an obvious question - if successfully CRISPR’d cells can seed cancers, why hasn’t this been seen before, and why haven’t the many CRISPR’d mice developed tumors?

Karolinska’s Haapaniemi said the effect shows up in large-scale experiments like hers and Novartis’ “but can be missed in small-scale studies where people only focus on editing one gene in one cell type.” In speaking to other scientists, she said, “it seems that other teams have noticed the effect of p53 on editing,” but have not highlighted it.