What happened

Shares of Bionano Genomics (BNGO -1.57%) rose 8.4% during market hours on Tuesday, only to fall roughly 10% after the market closed.

So what

Investors bid up Bionano's stock price after the biotech said on Monday that its Saphyr optical genome mapping (OGM) system could detect structural variants that could make people more likely to get severe forms of COVID-19.

Investors were also likely pleased when the results of a study released on Tuesday showed Saphyr could detect all clinically important variants of cancer genomes in people with myelodysplastic syndromes (MDS), precursors to acute myeloid leukemia (AML). Notably, Saphyr could do so in a single assay -- rather than the multiple tests required by current methods -- and thus potentially help patients receive care faster.

A finger points to a digital stock chart that rises sharply and then falls.

Bionano Genomics' stock reversed course on Tuesday. Image source: Getty Images.

However, Bionano's share price fell approximately 10% in after-hours trading after the company announced a public stock offering. Bionano did not disclose the number of shares it intends to sell.

Now what

Bionano previously completed a stock sale of roughly $100 million on Jan. 12. The company's decision to sell more shares so soon could mean management believes that in recent weeks Bionano's stock price might have risen too far, too fast.